OTA recommendations

[rabbit73]

By PM:
I've seen your posts on here that are extremely informative. That lead me to register here, looking for advice as a recent cord-cutter. Problem is, my account hasn't been approved yet so I don't have permission to post. Would you be ok if I sent you a PM with my details and you could re-post that for me on the "Help with Reception" subforum?

Thanks.
Hello, verder.

Many others have to wait because the TVFool staff is very small. Some never are able to post. This forum is becoming less active; it isn't as secure since they didn't renew their certificate. There is no longer https:// in the address.

If you get tired of waiting, you can join the AVS Forum:
https://www.avsforum.com/forums/hdtv-technical.25/

I will try to help you with your OTA problem under these difficult circumstances.

I will need certain information, like a signal report, a description of your present equipment, and what channels you hope to receive.

If you are willing to give me your address and coordinates of your antenna, I can get a signal report from rabbitears.info and look at your location in a satellite view.
https://www.rabbitears.info/searchmap.php

The signal reports from TVFool now contain errors because they are using an old database to generate reports.
https://www.tvfool.com/index.php?option=com_wrapper&Itemid=29

If this conversation continues, you should know that you are presently limited to 5 PM messages. If you don't delete the earlier PMs, I will get the message that your inbox is full.

rabbit

[rabbit73]

His reply by PM:
Thanks for all of the info. I'll take your advice and head over to the AVS forum. I'll post my info over there and see what I find out.

Thanks again!

[rabbit73]

Next reply by verder by PM:
Looking at that AVSForum site, I'm not sure where to post. I live in the Fargo area which has a 115 page thread already started, but just skimming through it, it looks like it's more about the market than specific antenna help. In fact, you were the last person to post in that thread two months ago! :)

So, here's my info if you are still interested in helping out. I already have a Clearstream 4Max installed on the east edge of my second floor roof (on the north side, about 2-3' up from the gutter). I have < 100' of copper-clad dual shield RG6 running west under my eave and into my house. The mast and cable is grounded. The path for the signal is: antenna -> cable -> grounding block -> cable -> internal cable jack plate -> cable -> Tablo. In other words, no splitting and only a couple of interconnects.

Before I permanently attached the antenna to my house, I made a temporary stand and tried several locations along the west and east sides of my house & garage. Part of my problem is that I have trees that are to the northwest and southeast, right in line with reported towers, and I was hoping to figure out where my "sweet spot" antenna location was. I ran the RG6 to a cheap MediaSonic digital tuner I picked up from Amazon that was connected to a TV via HDMI. I used that to get a rough signal quality reading and also would watch one channel on each carrier frequency for a minute or two to look for drop-outs or pixelation. The best place seemed to be on the east side of the house.

The funny thing about antenna placement is that I had the antenna temporarily at a point about halfway up to the peak of the house and got everything but KRDK. I didn't have any place for a ladder for permanently attaching things, so I moved my temporary stand down the slope of the house by a foot or two to the north and that got everything. Weird. RF reception almost seems to have a certain degree of black magic involved with it! :P

Note that I didn't go to the peak of my house mainly because I have the top of my fireplace chimney jutting out there -- it's a metal cylinder roughly 2' in diameter and I was thinking signal reflection / shielding may be an issue if I got too close. Additionally, trying to attach to the fascia there would have been challenging as I don't have a long enough ladder to reach that position.

Channels checked:

4-1 (KRDK)
6-1 (WDAY)
11-1 (KVLY)
13-1 (KFME)
15-1 (KVRR)
28-1 (K28MA)
30-1 (KXJB)

I now have the antenna connected to a Tablo Quad (4-tuner) DVR. The problem I'm having right now is that I occasionally get dropped recordings for channels 4, 11, 15, and 28. It doesn't happen all the time. I'm questioning if it is the Tablo or the antenna. I've heard that the Clearstream 4Max has a narrow signal reception angle, and I'm wondering if a cheaper RCA ANT751E from Menard's would be a better option:

https://www.menards.com/main/electrical/electronics/antennas/rca-compact-digital-hd-outdoor-attic-tv-antenna/ant751e/p-1444424448831-c-1454940301502.htm

I'm sure it doesn't help that I have towers almost 180 degrees apart. I need to receive both from the northwest and the southeast.

I don't have any fancy antenna equipment, but if it helps I do have an RTL-SDR and Airspy R2 SDR. I've been able to see the frequency spectrum that my antenna is putting out in the VHF/UHF bands. I was hoping to use that to see if I could tune things.

I looked up nearby cell tower locations on http://antennasearch.com/default.asp and there are some towers that are somewhat close to my location. I gave an LTE filter a shot, not really expecting much, and sure enough -- I still get weak signal indications so I think that was a bust.

Thanks for any help you can provide!
Thank you for the very thorough additional information.

We will study your problem and come back with some comments that might be helpful.

[rabbit73]

Here is a signal report for your location:
https://www.rabbitears.info/searchmap.php?request=result&study_id=143302

https://i.imgur.com/EzhDH6w.jpg

For comparison, a TVFool signal report for your location would look like this:
http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d9038e93d573093

https://i.imgur.com/0Rt3JPz.jpg

I don't think verder can see attachments yet. There are regular attachment to this post, and the images in the post are from my image host imgur.

[rabbit73]

Thanks for posting that info. Yes, you can show that picture in the thread.

OK, thanks

https://i.imgur.com/fF97XbO.jpg

How did you get those tower line of site overlays into that picture? That's very cool!
I used the TVFool Interactive Browser:
https://www.tvfool.com/?option=com_wrapper&Itemid=90

The green signal lines are based on old channel data, but it gives the general idea.

https://i.imgur.com/EzhDH6w.jpg

Channels checked:

4-1 (KRDK) COZI, Real channel 24, 324.8 deg True, Signal Margin 39 dB
6-1 (WDAY) ABC, Real channel 21, 306.1 deg True, Signal Margin 68 dB
11-1 (KVLY) NBC/CBS, Real channel 36, 331.6 deg True, Signal Margin 53 dB
13-1 (KFME) PBS, Real channel 13, 307.5 deg True, Signal Margin 59 dB
15-1 (KVRR) Fox, Real channel 19, 111.7 deg True, Signal Margin 56 dB
28-1 (K28MA) CBS/CW, Real channel 28, 331.6 deg True, Signal Margin 40 dB
30-1 (KXJB) CBS/CW, Real channel 30, 101.7 deg True, Signal Margin 60 dB

I now have the antenna connected to a Tablo Quad (4-tuner) DVR. The problem I'm having right now is that I occasionally get dropped recordings for
channels
4-1
11-1
15-1
28-1

It doesn't happen all the time. I'm questioning if it is the Tablo or the antenna.
I have no experience with the Tablo. How do the problem channels do with a TV tuner?
I've heard that the Clearstream 4Max has a narrow signal reception angle, and I'm wondering if a cheaper RCA ANT751E from Menard's would be a better option:
https://www.menards.com/main/electrical/electronics/antennas/rca-compact-digital-hd-outdoor-attic-tv-antenna/ant751e/p-1444424448831-c-1454940301502.htm

That version of the 751 has fewer elements than the original 751.
I'm sure it doesn't help that I have towers almost 180 degrees apart. I need to receive both from the northwest and the southeast.
The CS MAX4 does have a narrow beamwidth, but since it doesn't have a reflector, it is bi-directional.

[rabbit73]

I don't have any fancy antenna equipment, but if it helps I do have an RTL-SDR and Airspy R2 SDR. I've been able to see the frequency spectrum that my antenna is putting out in the VHF/UHF bands. I was hoping to use that to see if I could tune things.
A spectrum analyzer can be very useful. It will allow you to check the SNR.

https://i.imgur.com/bVDpfOz.jpg

The RTL-SDR.COM V3 dongle doesn't show a whole channel with the SDR# (SDRsharp) software, but it will show part of a channel, the pilot, and the adjacent noise floor, which is sufficient to estimate the SNR.

https://i.imgur.com/3bNbdYN.jpg

To show more than one channel, there is free open-source software for the dongle, but it isn't ready to use; you have to assemble it in a folder from GitHub.

https://i.imgur.com/7E42YTv.jpg

I like the Airspy R2 with the Spectrum Spy software.

https://i.imgur.com/tpkpAkb.jpg

https://i.imgur.com/6PODjZr.jpg

The dB scale is only relative, not absolute.

[rabbit73]

You asked in the thread about Tablo vs the TV tuner. I've only really used the TV tuner to do the original setup (finding the sweet spot.) From that point it's been pretty much using the Tablo exclusively. I have not used the MediaSonic TV tuner for an extended period of time.

That said, I'll do some experimentation and some longer viewing with it on the channels I've had issues with to see if there's anything unique with that (drop-outs or what-have-you.) Thankfully the Tablo has been recording what station, day, and times the problems are occurring. I'm starting to record that info in a spreadsheet to see if I can see a pattern or anything emerge.

It's not much, but one experiment I performed has been to find the pilot frequency for each channel using my Airspy R2 + SDR#. The Airspy has a wide enough bandwidth so I can see the "whole" signal at once. I used this to see what gain setpoints I needed to place that pilot frequency peak at -40dB to -45dB. The Airspy gain setpoints ranged from 3 to 13:

KFME: 6
KVRR: 7
WDAY: 3
KRDK: 8
K28MA: 13
KXJB: 8
KVLY: 10

I realize this doesn't show any sort of bit error info or whether I've got multipath issues going on, but I'm at least able to "see" things.

Thanks for help so far and relaying my posts to the thread!!!
Yes, you can see the whole channel with the Airspy R2 and SDR#.

https://i.imgur.com/NOyvwbS.jpg

For signal quality, SNR and errors, I use my SONY TV and a SiliconDust HDHR.

Bad signal

https://i.imgur.com/Z1S39Gx.jpg

Good signal

https://i.imgur.com/4XpqDzV.jpg

https://i.imgur.com/IVW8V3y.jpg

Signal Quality is similar to SNR.

Symbol Quality is the inverse of uncorrected errors; it should be 100%.

Looking at the shape of a signal can help find the best location for the antenna.

https://i.imgur.com/YSrnllZ.jpg

https://i.imgur.com/CeyHgSw.jpg

https://i.imgur.com/qNhHmFC.jpg

https://i.imgur.com/ErIg4Gw.jpg

The above three images were made with an SDRplay RSP1A and SDRuno software.

[eclipsme]

To show more than one channel, there is free open-source software for the dongle, but it isn't ready to use; you have to assemble it in a folder from GitHub.



What software is this? Thanks!

[rabbit73]

What software is this? Thanks!
It was difficult for me to assemble the software; I'm not an expert with software. I was about ready to give up, but on the third try I got it to work.

Pete Higgins had a tutorial on the HDF forum, but that forum folded. There is part of it on the web archive. Post #12 has the best INFO on the RTL-SDR Scanner:
https://web.archive.org/web/20170627172716/http://www.highdefforum.com/local-hdtv-info-reception/143795-inexpensive-software-defined-radio-spectrum-analyzer-10-00-a.html

I tried 3 different software versions that are listed in this post. I like the 64 Bit v1.3.0 RTLSDR Scanner best
https://www.digitalhome.ca/threads/converting-uhf-yagi-to-a-vhf-antenna.287147/page-5#post-3090963

RTLSDR Scanner
https://eartoearoak.com/software/rtlsdr-scanner

Releases
https://github.com/EarToEarOak/RTLSDR-Scanner/releases

go to v1.3.0 and click on assets if you have a 64-bit computer
click on rtlsdr_scan-windows-64bit.exe 41.1 MB

[eclipsme]

It was difficult for me to assemble the software. I was about ready to give up, but on the third try I got it to work.

Pete Higgins had a tutorial on the HDF forum, but that forum folded. There is part of it on the web archive. Post #12 has the best INFO on the RTL-SDR Scanner:
https://web.archive.org/web/20170627172716/http://www.highdefforum.com/local-hdtv-info-reception/143795-inexpensive-software-defined-radio-spectrum-analyzer-10-00-a.html

I tried 3 different software versions that are listed in this post. I like the 64 Bit v1.3.0 RTLSDR Scanner best
https://www.digitalhome.ca/threads/converting-uhf-yagi-to-a-vhf-antenna.287147/page-5#post-3090963

I see what you mean. Lots of pieces to be obtained from lots of places.
Thanks!
Was it worth it? Nice cheap alternative for someone that barely understands what this is!

[rabbit73]

I see what you mean. Lots of pieces to be obtained from lots of places.
Thanks!
Was it worth it? Nice cheap alternative for someone that barely understands what this is!
It was worth it to me; it gave me a spectrum analyzer for $25. I was then able to see if the channel was there when my tuner didn't pick it up during a channel scan.

The first thing I did when learning about SDRs was download the SDR# (SDRsharp) software, which was ready to use. The dongle and SDR# will only show about 2 MHz. But, I was then able to look at part of a channel, its pilot carrier, and estimate the SNR of the channel.

https://i.imgur.com/3bNbdYN.jpg

I was also able to look at and listen to FM signals.

https://i.imgur.com/dO83B4D.jpg

This gave me the confidence to try the spectrum analyzer for the RTL-SDR.COM V3 dongle.
https://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/

I knew that if I couldn't figure out the RTLSDR Scanner, I would at least have the dongle and SDR# software.

I suggest you try the RTL-SDR.COM V3 dongle with the SDR# software to give you confidence.
Quick Start Guide
https://www.rtl-sdr.com/rtl-sdr-quick-start-guide/
Installing RTL-SDR & SDR Sharp on Win10 Made Easy - TheSmokinApe
https://www.youtube.com/watch?v=rUwRt5qn-6U

Once you have it working, then you need to learn how to adjust the gain to make a good estimate of the SNR of the channel. There is an optimum setting of the gain to show max signal with max SNR. Strong signals require less gain; weak signals require more gain.

https://i.imgur.com/dgVvfhj.jpg

This is my amateur video; one of these should work:

https://www.dropbox.com/s/ge923irqji75p4q/SDR%23%20v1.0.0.1732%20-%20RTL-SDR%20%28USB%29%202020-09-01%2014-50-56.mp4?dl=0 (https://www.dropbox.com/s/ge923irqji75p4q/SDR%23%20v1.0.0.1732%20-%20RTL-SDR%20%28USB%29%202020-09-01%2014-50-56.mp4?dl=0)

https://www.dropbox.com/s/ge923irqji75p4q/SDR%23%20v1.0.0.1732%20-%20RTL-SDR%20%28USB%29%202020-09-01%2014-50-56.mp4?dl=1

If you want to show the whole channel with ready-to-use software, then upgrade to the SDRplay RSP1A SDR ($100) with SDRuno software.

https://i.imgur.com/CeyHgSw.jpg

[eclipsme]

It was worth it to me; it gave me a spectrum analyzer for $25. I was then able to see if the channel was there when my tuner didn't pick it up during a channel scan.

The first thing I did when learning about SDRs was download the SDR# (SDRsharp) software, which was ready to use. The dongle and SDR# will only show about 2 MHz. But, I was then able to look at part of a channel, its pilot carrier, and estimate the SNR of the channel.

https://i.imgur.com/3bNbdYN.jpg

I was also able to look at and listen to FM signals.

https://i.imgur.com/dO83B4D.jpg

This gave me the confidence to try the spectrum analyzer for the RTL-SDR.COM V3 dongle.
https://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/

I knew that if I couldn't figure out the RTLSDR Scanner, I would at least have the dongle and SDR# software.


This is not looking too difficult. SDRSharp is downloaded as a zip file and rtlsdr scanner has an installation file. The scanner is what allows you to see the entire channel (or multiples), right?

I almost stumbled by buying a clone but now I understand what to buy.

In another post, you advised me to point my antenna towards Orlando rather than Palm Beach. I have done so to good effect. CBS in Orland came in 80-100% right away, but then to 0 and back again. I want to use the scanner to lock in that station.

Sorry to appropriate the thread from the OP.

[rabbit73]

This is not looking too difficult. SDRSharp is downloaded as a zip file and rtlsdr scanner has an installation file. The scanner is what allows you to see the entire channel (or multiples), right?
Uh, no; not exactly. I edited my post #11 above and added an image and a video. Please look at it.

I have used 3 SDRs:

https://i.imgur.com/2E2nvoV.jpg

For $25 you can buy an RTL-SDR.COM V3 dongle and download SDR# software. With it you will only be able to see part of a TV channel. The dongle will only show about 2 MHz, not a whole TV channel which is 6 MHz wide.

If you use the free open-source DIY spectrum analyzer software (RTLSDR Scanner) for the dongle, you can see more than one channel. You have to assemble the software yourself in a folder to use it. The way it is able to show more than one channel is by stitching together sections to make the entire scan.

If you want to see the whole channel with ready-to-use software, you have to buy an SDRplay RSP1A SDR ($100) and download the SDRuno software.

If you want a spectrum analyzer with ready-to-use software you have to buy an Airspy R2 SDR ($200) and download the SDR# software which will include the Spectrum Spy Spectrum Analyzer software.
Sorry to appropriate the thread from the OP.The OP and I are both interested in SDRs and feel that they are a useful tool for solving reception problems. I don't think we went too far off topic.

[rabbit73]

Back on topic
From PM:
I'll use Spectrum Spy across the UHF band and take a screen capture of what I see. I've only looked at individual channels using SDR#, and that was after tweaking the gain for each.

This makes me wonder how the Tablo tuner operates. "How do it know" that it needs to crank the gain for some channels but also not crank it as high for channels that are coming in loud and clear? It's got 4 separate tuners, so it presumably should be able to dynamically adjust the gain based on whatever channel each tuner is being tuned to. Obviously, gain doesn't mean much if there's a lot of noise or interference that is distorting the original signal.

As always, thanks for your insight!
I assume that there is an internal amp to compensate before splitting to four tuners like in the TiVo. Each tuner should have its own AGC in use for the particular channel used by that tuner.

Ideally, the AGC shouldn't alter the SNR of the signal unless it is extremely strong or extremely weak; IOW, within its operating range.

Your additional tests should give you more clues.

Since your two directions are almost 180 degrees apart, you will need a bi-directional antenna or 2 separate antennas. The ANT 751 is not bi-directional, but your AD 4MAX is bi-directional since it doesn't have a reflector. I have some concern about the 4MAX because of its narrow beamwidth. If its aim is optimum for one direction, it might be off for the other direction.

A DB4e without a reflector would have a wider beamwidth, but perhaps not quite as much gain.

It looks like your present antenna location can "see" in both directions, but the antenna might not be high enough for the signals to clear the trees. Trees can seriously affect the incoming signals, especially when they are wet. Also, when the wind moves the branches it creates multipath problems.
http://www.hdtvprimer.com/ANTENNAS/siting.html
scroll down to Trees and UHF

You mentioned earlier that when you moved the antenna higher, you lost a channel. This seems counterintuitive, but is caused by layering:

https://i.imgur.com/MWtGdqn.jpg

I'm presently living in a retirement facility on lockdown. My previous room was on the first floor and an indoor antenna did quite well. When I was moved to the 2nd floor, I thought the additional height would help, but there is a tree in the signal paths.

https://i.imgur.com/YSrnllZ.jpg

and when the wind blows, it really messes with the signal:
https://www.dropbox.com/s/8gsw9t1zsr7mpxo/CH16TreeInPath2.mp4?dl=0

https://www.dropbox.com/s/8gsw9t1zsr7mpxo/CH16TreeInPath2.mp4?dl=1

this is what the signal looks like with a strong wind:
https://www.dropbox.com/s/ig3va499k237ayu/CH16TreeInPath4.mp4?dl=0

https://www.dropbox.com/s/ig3va499k237ayu/CH16TreeInPath4.mp4?dl=1

[eclipsme]

Uh, no; not exactly. I edited my post #11 above and added an image and a video. Please look at it.

I have used 3 SDRs:

https://i.imgur.com/2E2nvoV.jpg

For $25 you can buy an RTL-SDR.COM V3 dongle and download SDR# software. With it you will only be able to see part of a TV channel. The dongle will only show about 2 MHz, not a whole TV channel which is 6 MHz wide.

If you use the free open-source DIY spectrum analyzer software (RTLSDR Scanner) for the dongle, you can see more than one channel. You have to assemble the software yourself in a folder to use it. The way it is able to show more than one channel is by stitching together sections to make the entire scan.

If you want to see the whole channel with ready-to-use software, you have to buy an SDRplay RSP1A SDR ($100) and download the SDRuno software.

If you want a spectrum analyzer with ready-to-use software you have to buy an Airspy R2 SDR ($200) and download the SDR# software which will include the Spectrum Spy Spectrum Analyzer software.
The OP and I are both interested in SDRs and feel that they are a useful tool for solving reception problems. I don't think we went too far off topic.

RTLSDR Scanner is available as executable install. Hopefully making this part much easier:
https://github.com/EarToEarOak/RTLSDR-Scanner/releases

Your video quite nicely shows the affect of the gain control. I look forward to playing with this.

I have the dongle on order, along with an adapter. Should be here tomorrow...

[rabbit73]

RTLSDR Scanner is available as executable install. Hopefully making this part much easier:
https://github.com/EarToEarOak/RTLSDR-Scanner/releases

Your video quite nicely shows the affect of the gain control. I look forward to playing with this.

I have the dongle on order, along with an adapter. Should be here tomorrow...
I'm glad the video helped you; it is an important concept when using the dongle with SDR#.

Adjusting the gain of the RTLSDR Scanner is a little different. You raise the gain until the noise floor starts to rise and then stop. More precisely, when it starts to rise you back it off a little.

Gain set too low:

https://i.imgur.com/RafmluQ.jpg

Correct gain setting:

https://i.imgur.com/7E42YTv.jpg

Gain set too high:

https://i.imgur.com/RMT569M.jpg

With the RSP1A and Airspy R2 you adjust the gain and other contols for max SNR.

Good luck with your adventure.

[rabbit73]

Part of my problem is that I have trees that are to the northwest and southeast, right in line with reported towers, and I was hoping to figure out where my "sweet spot" antenna location was.
I looked at some satellite and ground views of your location. I think the trees are a significant part of your reception problem; they appear to be taller than your antenna.

I will not post any images without your permission.

[rabbit73]

Yes, I agree trees are the biggest problem. I'd have to get a quite a tall pole to be able to reach an unobstructed view. I don't think that's going to happen so I may just have to live with the occasional drop in signal.

Thanks.

https://i.imgur.com/fF97XbO.jpg

I think you have done a good job finding the best antenna location available on your property without going to extreme measures like a push-up mast with guy wires in the back yard.

Your signal report indicates that a preamp isn't necessary, but the actual signals arriving at your antenna might be weaker because of the trees.

The only other possibility I can think of is an antenna with a wider beamwidth.

If you used two antennas, one for each direction, there would be the problem of combining them or having to switch them.

https://i.imgur.com/THktXAU.jpg

Channels checked:

4-1 (KRDK) COZI, Real channel 24, 324.8 deg True, Signal Margin 39 dB
6-1 (WDAY) ABC, Real channel 21, 306.1 deg True, Signal Margin 68 dB
11-1 (KVLY) NBC/CBS, Real channel 36, 331.6 deg True, Signal Margin 53 dB
13-1 (KFME) PBS, Real channel 13, 307.5 deg True, Signal Margin 59 dB
15-1 (KVRR) Fox, Real channel 19, 111.7 deg True, Signal Margin 56 dB
28-1 (K28MA) CBS/CW, Real channel 28, 331.6 deg True, Signal Margin 40 dB
30-1 (KXJB) CBS/CW, Real channel 30, 101.7 deg True, Signal Margin 60 dB

I now have the antenna connected to a Tablo Quad (4-tuner) DVR. The problem I'm having right now is that I occasionally get dropped recordings for
channels
4-1
11-1
15-1
28-1

It doesn't happen all the time. I'm questioning if it is the Tablo or the antenna.

[rabbit73]

Here's the SpectrumSpy trace from my antenna:

https://imgur.com/a/XMGGyx7

https://i.imgur.com/iTqlYVK.jpg

Thank you for the UHF scan; nicely done.

KVRR virtual 15-1 RF 19 shows a little more than the minimum SNR for reception, but could be a problem at times

WDAY virtual 6-1 RF 21 is your strongest channel; shouldn't be a problem

KRDK virtual 4-1 RF 24 is a little stronger than KVRR; could be a problem at times

K28MA virtual 28-1 RF 28 is very weak; doesn't look strong enough for tuner lock in this scan

KXJB virtual 30-1 RF 30 is fairly strong but shows possible multipath problem. It is listed as second in strength after WDAY, but is a low power station
https://www.rabbitears.info/tvq.php?request=items&facid=185885

KVLY virtual 11-1 RF 36 shows just barely enough SNR for a tuner lock and would be expected to have problems

This is my UHF; CH 14 doesn't decode. I like to show the settings and have added arbitrary numbers to the gain scale. I bring the gain up until the noise floor just starts to rise and stop, which should show the correct SNR.

https://i.imgur.com/bHeqKJF.jpg

The weak signals got a little better this evening:
Videos, no audio

https://www.dropbox.com/s/eusj9k25wg1jbtn/Spectrum%20Spy%202020-09-03%2019-08-07.mp4?dl=0

https://www.dropbox.com/s/eusj9k25wg1jbtn/Spectrum%20Spy%202020-09-03%2019-08-07.mp4?dl=1

Here is FM and VHF-High, no audio
CH 7 is around 175 MHz; it is damaged by multipath and doesn't decode
CH 11 is around 200 MHz and usually does OK; the noise level is high

https://www.dropbox.com/s/fnjyuttou2l0php/Spectrum%20Spy%202020-09-03%2019-54-35.mp4?dl=0

https://www.dropbox.com/s/fnjyuttou2l0php/Spectrum%20Spy%202020-09-03%2019-54-35.mp4?dl=1

[rabbit73]

You mentioned: "The only other possibility I can think of is an antenna with a wider beamwidth." Is there anything available that is at least 180deg bidirectional that has a wider beam width? Is the ClearStream 4Max as good as I'm going to get, or are there alternatives?
I had thought that a Antennas Direct DB4e with the reflector removed might be worth a test. You would have to add a dipole for VHF channel 13.

I will try to find some antenna patterns; they are getting hard to find.

[rickbb]

I had thought that a Antennas Direct DB4e with the reflector removed might be worth a test. You would have to add a dipole for VHF channel 13.

I will try to find some antenna patterns; they are getting hard to find.

If the OP is handy with tools he might try to look into Mclapps 4 bay 10.5 x 9 design. I use this with no reflector and get channels from both front and back as well as VHF 11 from about 50 miles from the tower quite well. As a worst case he will have a 4 bay test antenna for less than $30.

[rabbit73]

If the OP is handy with tools he might try to look into Mclapps 4 bay 10.5 x 9 design. I use this with no reflector and get channels from both front and back as well as VHF 11 from about 50 miles from the tower quite well. As a worst case he will have a 4 bay test antenna for less than $30.
Yes, that is a good idea for a DIY antenna.

https://i.imgur.com/FFvapU1.jpg

http://www.m4antenna.eastmasonvilleweather.com/index.html

https://i.imgur.com/TtVlJdn.jpg

https://i.imgur.com/T0WrezT.jpg

https://i.imgur.com/iCu4RdB.jpg

Looks like the whisker length and vertical spacing of the bays should be increased for the new 14 - 36 UHF band.

[OTAFAN]

The links above and here to the Mclapp UHF antenna are not secure, but neither is TV Fool presently. Here's everything but the kitchen sink, including a YouTube video:

https://sites.google.com/site/maycreates/ota-setup/mclapp-4

https://www.youtube.com/watch?v=4dNP4vuQ9Z0

Outstanding work as usual, rabbit73!

All the best.....

[rabbit73]

I saw the antenna plans. I've actually considered putting together a Gray-Hoverman antenna. That might be a good Labor Day project!
You might need to do the GH with NARODS for PBS.

I'm considering getting either a cheap HDHomeRun or perhaps a Hauppauge TV tuner. These include signal meter, signal quality, and symbol quality information that are provided by GUIs / phone apps. Curious if others out there have gone this route and what signal information they've been able to use to their advantage.
I compared the two. Both work, but I prefer the HDHR.

https://i.imgur.com/GW4yD4y.jpg

https://i.imgur.com/VyLeSIU.jpg

https://i.imgur.com/Maxu7wk.jpg

https://i.imgur.com/IVW8V3y.jpg

https://i.imgur.com/OXRaWNB.jpg

https://i.imgur.com/UUX3SOM.jpg

Here is a calibration chart for the HDHR. 100% SS is 0 dBmV = -48.8 dBm. Actually it's calibrated in the factory for 60 dBuV = 0 dBmV. Antenna installers and cable guys in other countries use dBuV instead of dBmV.
https://i.imgur.com/S4o4c6x.jpg

Tuners can handle much stronger signals.

https://i.imgur.com/USrn73K.jpg

I'm currently in contact with Tablo support to see why I'm getting pixelation and failed recordings. I asked about their device providing real-time diag info. They said their engineers are investigating supplying this info, but there is nothing definite at this point.
I wonder if the Tablo tuner is as good as a TV tuner, especially with multipath caused by the trees. If you made a side by side comparison, you might need a low gain preamp before splitting; 100 ft of coax acts like a 5 dB attenuator for UHF. If you mount a preamp at the antenna, it should be a medium gain preamp resistant to overload.

[rabbit73]

This is a simulation of the DB4e antenna pattern with the reflector removed. Most other 4-Bay antennas would be similar:

https://i.imgur.com/7WPpAYo.jpg

Since the antenna is now bi-directional, the gain will be reduced by about 3 dB.

If you combine two CS2 antennas side by side, you get a CS4. The CS4 has more gain, but the beamwidth is more narrow; there is no free lunch.

https://i.imgur.com/eBCCl2X.jpg

Antennas Direct used to publish technical documents that showed antenna patterns. I couldn't find one for the C4MAX, so I had to create this simulation:

https://i.imgur.com/h5krcV3.jpg

Since the C4MAX doesn't have a reflector, its pattern is bi-directional and the gain will be about 3 dB less than indicated for the C4.

[rabbit73]

I now have the antenna connected to a Tablo Quad (4-tuner) DVR. The problem I'm having right now is that I occasionally get dropped recordings for
channels
4-1
11-1
15-1
28-1

It doesn't happen all the time. I'm questioning if it is the Tablo or the antenna.
Channels checked:

4-1 (KRDK) COZI, Real channel 24, 324.8 deg True, Signal Margin 39 dB
6-1 (WDAY) ABC, Real channel 21, 306.1 deg True, Signal Margin 68 dB
11-1 (KVLY) NBC/CBS, Real channel 36, 331.6 deg True, Signal Margin 53 dB
13-1 (KFME) PBS, Real channel 13, 307.5 deg True, Signal Margin 59 dB
15-1 (KVRR) Fox, Real channel 19, 111.7 deg True, Signal Margin 56 dB
28-1 (K28MA) CBS/CW, Real channel 28, 331.6 deg True, Signal Margin 40 dB
30-1 (KXJB) CBS/CW, Real channel 30, 101.7 deg True, Signal Margin 60 dB

https://i.imgur.com/VqaxZOA.jpg

https://i.imgur.com/jSik199.jpg

[rabbit73]

Yesterday I assembled an MClapp antenna out of spare 12-2 copper wire I had laying around. I also made a Gray-Hoverman w/NARODs (no reflector version) using 8 gauge bare copper wire I picked up at the Big Orange Box Store. :)

I haven't tried either one at elevation -- just in my backyard at ground level to see what SpectrumSpy reported. Nothing to write home about but it's more or less what I expected. The siding from my house + the siding from the shed + the trees + ground elevation all come together I'm sure to attenuate things.

Today's fun will be to see if either are suitable for attic installation. I'm using a simple wood "backbone" for assembly so neither would survive the elements. I'm also curious about how well (or horrible) an attic installation is. The thing about the attic is that somewhat near my network center where my Tablo is, so I'd be able to deal with a much shorter run of cable (not that my current run is all that excessive.) From there, I'll probably look into mounting things on PVC tubing and mount it near the location of the 4Max.

Last night, I also happened on discussion about the Antop AT-400BV. I think that would be an interesting antenna to try out. If it's a bust I could always return it.

Finally, I'm working with Tablo support on Tablo to see why my failed recordings are happening. I'm curious to find out what they say.
Sounds like you have some interesting experiments planned.

[rabbit73]

One additional note -- I wonder if the ClearStream 2Max would be another option in terms of beamwidth. From what I understand, it's wider than the 4Max. Maybe I bought "too much" antenna when I picked the 4Max? Then again, if I have potential issues with multipath interference, widening the beamwidth might induce other issues that the 4Max avoids? :P
The 2MAX does have a wider beamwidth than the 4MAX, and less gain on axis. It also probably has less gain than a 4-Bay.

[rabbit73]

It's not much, but one experiment I performed has been to find the pilot frequency for each channel using my Airspy R2 + SDR#. The Airspy has a wide enough bandwidth so I can see the "whole" signal at once. I used this to see what gain setpoints I needed to place that pilot frequency peak at -40dB to -45dB. The Airspy gain setpoints ranged from 3 to 13:

KFME: 6
KVRR: 7
WDAY: 3
KRDK: 8
K28MA: 13
KXJB: 8
KVLY: 10

I realize this doesn't show any sort of bit error info or whether I've got multipath issues going on, but I'm at least able to "see" things.

Thanks for help so far and relaying my posts to the thread!!!
Using the pilot is certainly helpful in finding a channel, but the strength of the pilot is not a reliable measurement for the strength of the channel. Multipath reflections can affect the strength of the pilot without making a comparable change in the strength of the channel.

Analog TV signals use a peak measurement of the video carrier, but the strength (actually power) of a digital TV channel is the average power across the whole channel.

https://i.imgur.com/sLPqJdr.jpg

If you look at your scan, you might be able to see that there isn't always a good correlation between the average power of the channel and the strength of its pilot, like KXJB vs KVLY, or KVRR vs KRDK.

https://i.imgur.com/iTqlYVK.jpg

I think a better indicator of the signal quality of a channel is the SNR of the channel implied by the scan when the gain of the of SDR# or Spectrum Spy software is properly adjusted for max SNR. Bring the gain up to the point just before the adjacent noise floor starts to rise.

Video of adjusting gain for CH 31
I should have shown some of waterfall so that the freq scale would show

https://www.dropbox.com/s/hzmz4mvte45fwy9/SDR%23%20v1.0.0.1732%20-%20AIRSPY%202020-09-05%2018-50-57.mp4?dl=0

https://www.dropbox.com/s/hzmz4mvte45fwy9/SDR%23%20v1.0.0.1732%20-%20AIRSPY%202020-09-05%2018-50-57.mp4?dl=1

CH 16

https://www.dropbox.com/s/0jlgno1gtjpwev8/SDR%23%20v1.0.0.1732%20-%20AIRSPY%202020-09-05%2019-02-31.mp4?dl=0

https://www.dropbox.com/s/0jlgno1gtjpwev8/SDR%23%20v1.0.0.1732%20-%20AIRSPY%202020-09-05%2019-02-31.mp4?dl=1

The difference between the adjacent noise floor and the average level of the top of the signal that you see on the screen is a fairly good estimate of the SNR. However, it might not be exactly the same as the SNR given by the TV diagnostics menu. It would be difficult for the TV to measure the level of the noise floor when the channel is in use. What the TV is giving is actually the MER (Modulation Error Ratio) which is derived from the constellation diagram. The MER includes the affects of impediments like multipath errors.
https://blog.solidsignal.com/tutorials/dtv-antenna-help-touch-snr-ber-mer/

[rabbit73]

Not all tuners are equal
(If you are becoming tired of copying these PMs to the main thread, let me know and I can try bringing this conversation over to the AVS forums if you know of a good spot for them.)
It doesn't take a lot of time to post your messages, but it does take a lot of my time to think of useful answers. However, I find your reception problem interesting and I always learn something new when helping a poster.

I am willing to stick with it a little longer; it's kind of peaceful here. When I run out of ideas, it's time for you to go to AVS for some new ideas.
Today's experiments consisted of some simple bench top testing and some garage rafter testing. The bench top testing was literally bench top. I've got a workbench in my garage and just placed the Gray-Hoverman build facing due south. I did that to perform some sanity checking with the Airspy R2 on my build. Turns out that I've apparently got some issues with the R2 where I see spikes every 8MHz no matter what center frequency I'm at. These appear at a mid-gain setting. This happens with no antenna, with antenna, USB cable swapped, computer swapped, within SDR# and within SpectrumSpy. I've got a support request in to Airspy US to see what may be the problem... could be between the chair and the keyboard (ha!), but I don't think I'm doing anything different from before and the behavior is certainly different.
It sounds like RF Interference from a switchmode power adapter (SMPS) or a battery charger. The USB cable that I ordered with my R2 has two ferrite beads on it. Without a signal, I get some noise spikes when using my RTL-SDR dongle, but I don't let it bother me. The noise spikes are greatly reduced when a signal is present.

https://i.imgur.com/hQXDtBd.jpg

Unfortunately, the Gray-Hoverman frame turned out to be too big for my rafters, so I switched over to the Mclapp. I used a 50' dual-shield RG6 coax line to run from my rafters to a splitter on my workbench. The splitter feeds 2x identical Dynex TVs. One was set to the internal digital tuner and the other was connected to a cheap MediaSonic digital tuner via HDMI input. The Dynex TVs have a "Channel Strength" reading and the MediaSonic has a "Quality" reading that I referenced.

It turns out that Channel Strength and Quality don't amount to much. In the rafters with the antenna pointed towards the northwest towers, I'd have "Good" (highest Dynex reading) and would see pixelation / drop-out. With the MediaSonic quality almost always about 50%, I'd see it drop-out down to 0% (signal loss).

Testing involved tuning to each 'main' channel for 2 minutes (that is, I didn't bother checking any of the multiplexed channels from a particular tower). One minute was spent watching the channel, looking for signal loss, pixelation, or audio issues, and another minute was spent bringing up the Strength/Quality reading and looking for the worst case value over that period of time.

I had both TVs going simultaneously. One displayed the MediaSonic decoding and the other the internal TV tuner. (I realize the splitter produces -3.5dB loss, but I assume a 50ft run and nothing else wouldn't impact things too much and an amplifier was not necessary. Tell me if I'm wrong.)
Using a splitter is a good way to make a real-time comparison, but you have a signal loss of about 5 dB for the splitter and coax combined. That's too much loss; your signals are already too weak. Try a moderate amount of amplification before splitting.
Here's where things get... interesting. After about 15 minutes of watching KVRR/CH19 (I was sitting there having supper in my garage and decided to do an extended watch), I saw the MediaSonic drop out a few times. During this time the internal Dynex tuner did not miss a beat. The MediaSonic seemed to have trouble whereas the Dynex didn't. Hm. I watched a bit longer. I saw a couple of occasions where they both dropped out. Okay. That sucks but made sense. It seemed like the MediaSonic was a piece of junk where the Dynex dominated. I then changed the channel to KRDK/CH24. The reverse happened. The MediaSonic dominated and the Dynex internal tuner crapped out -- even so bad that I had to power cycle the television. On top of that, I saw both having issues -- but they were intermittent. It took ~15 minutes of watching for the thing to show up. I never caught these problems in my quick onesie/twosie test.

This means that testing could be a massive time-sink. The dropouts on KVRR/CH19 didn't happen right away. Things were great for about 15 minutes like I said and then they flopped out. To me this means that I could perform the antenna aiming and think that everything works -- only to come back later and see that things die for an inexplicable reason. Needless to say, this is a bit frustrating and deflating.
Most of your signals are marginal, which means they are very close to the digital cliff. It is true that all tuners are not equal, but it only takes a small difference in a signal to make a big difference at the cliff. Don't sweat these small differences; OTA signals are constantly changing in strength. You need more signal margin before dropout. Focus on making all your signals stronger as they come out of the antenna before any amplification.
I do plan to test out the Gray-Hoverman still (I shortened the frame after I finished my testing for the night), but I'm kinda thinking that what I'm getting out of the 4Max is probably as good as it's going to get. Yeah, it drops out every once in a while, but this is probably just a nature of the OTA reception? Without adequate tools to monitor the various signal components (strength / quality / symbol quality / bit error rates / etc.), getting a good signal from my location is a bit of crap-shoot.
The tools that you already have are adequate. You can measure relative signal strength and SNR. The HDHR GUI will tell you how close you are to the critical 50% signal quality point, and tell you when you have 100% symbol quality which means no uncorrected errors.

Use those tools to improve signal strength and signal quality.

[rabbit73]

Unfortunately, I do not own an HDHomeRun yet so I don't have access to that additional signal information.
Sorry, I got a little ahead of you. I like my HDHR4-2US (the gray one); I avoided the 4-tuner models.

The signal quality reading from your MediaSonic tuner should help. At what percent reading does dropout happen? That point should be similar to the 50% signal quality point of the HDHR.
I had an old ViewSonics amplifier lying around (VSAV10-1000-2WZ w/a 10dB forward gain) and used that with the Gray-Hoverman antenna I built. I had the antenna in the same location as Mclapp that I played around with yesterday. Unfortunately, the reception today was worse than yesterday with the Mclapp. I need to go back to the Mclapp build and try it with the amplifier and see if that improves anything. The amplifier is pretty old (~2001) and has been sitting in the garage as a leftover from the previous owners. I'll look at running that experiment tomorrow. If I pick up a new amplifier, do you have any recommendations about what I should buy? I see box stores with amplifiers that range from 4dB to 20dB gains. Not sure how to correctly gauge what I should be looking for.

https://i.imgur.com/ccA0fsI.jpg

That is a cable drop amp. If it's working OK, it should be helpful. It should be placed close to the antenna to compensate for the coax and splitter loss. The 7 dB noise figure is a little high. I use a CM 3410 or a CM7777HD Amplify for that kind of indoor testing. For outside close to the antenna I would use a regular preamp like an Antennas Direct Juice or a CM 7778 V3. Avoid the RCA TVPRAMP1R; the quality control is poor. I bought two new ones in sealed boxes; both failed.

It's important to have a preamp close to the antenna for the best system noise figure. The first device in a system primarily determines the system noise figure as shown by the Friis Formula:
https://en.wikipedia.org/wiki/Friis_formulas_for_noise

Do I understand you correctly; you have your test antenna inside?

That would mean you have
tree loss,
building loss,
cable loss,
and splitter loss
before the signals get to your tuner.

That's not too different than mine; I have an indoor antenna behind a tree and cable loss (25 ft), but my antenna looks out a window to reduce building loss. My signal report is similar, except there is just one direction:

https://www.rabbitears.info/searchmap.php?request=result&study_id=145947

Today's experiments consisted of some simple bench top testing and some garage rafter testing. The bench top testing was literally bench top. I've got a workbench in my garage and just placed the Gray-Hoverman build facing due south. I did that to perform some sanity checking with the Airspy R2 on my build. Turns out that I've apparently got some issues with the R2 where I see spikes every 8MHz no matter what center frequency I'm at. These appear at a mid-gain setting. This happens with no antenna, with antenna, USB cable swapped, computer swapped, within SDR# and within SpectrumSpy. I've got a support request in to Airspy US to see what may be the problem... could be between the chair and the keyboard (ha!), but I don't think I'm doing anything different from before and the behavior is certainly different.

Regarding the Airspy issues: if I go to "Free" mode in SDR# and adjust the LNA Gain between a value of around 6-16 or so, I see the 'ghost' signal appear. Values outside of that range do not cause it to turn up. Jacking with the IF and Mixer gains don't cause any problems. Is it possible that the TV signals I was measuring the other day with SpectrumSpy did something to the LNA?
The signal would have to be extremely strong to damage your Airspy SDR. That's unfortunate that you are having trouble with your Airspy R2; they are expensive.

I don't completely understand your problem. Can you show us a photo?

Does your Airspy receive FM signals OK?

Have you tried a new download of SDR#?

Are you using an SMA to F adapter or an SMA to F adapter cable on the R2? I leave an adapter cable on all 3 of my SDRs to protect their SMA input connectors. If I just used a small metal SMA to F adapter for the RG6 to connect to the SDR it might weaken the SMA connector.

[rabbit73]

Here are a few screen caps: https://imgur.com/a/mIFfUUQ

Gain @ 8 -- no ghost
Gain @ 9 -- ghost signal appears to the right of an FM signal
Gain @ 9, shifted center frequency -- ghost slides along with the shifting.
Thank you for the images and the detailed explanation.

https://i.imgur.com/BBrbazI.jpg

https://i.imgur.com/UO1EckC.jpg

https://i.imgur.com/AzQcUvN.jpg

On SpectrumSpy it appears as a ghost signal that appears spaced at 8MHz intervals.

I assume Airspy support is out of the office today due to the holiday. Hopefully I hear back from them this week. I guess the device has a one year warranty so I may not be totally hosed:

Airspy Warranty
Airspy warranty is limited to 1 year from the date of delivery for purchased units that fail under normal operating conditions. Airspy units will be repaired at a price of $50.00 plus $10.00 shipping/handling. Normal operating conditions do not include excessive mechanical stresses due to mishandling, dropping, or bending; mechanical or electrical modifications; Electro-Static Discharge (ESD); excessive RF signals; excessive thermal stresses due to improper ventilation or cooling, submersion in any fluid; and any unauthorized repairs.
All warranty claims will be determined by Airspy or their representatives.
It appears to be an artifact that only shows at certain gain settings. When an SDR is designed, there are many stages. The goal of the design is to balance the gain of each stage so that they all stay within their normal operating range at all gain settings.

That is why it is so difficult to have an SDR dB scale with absolute instead of relative values. The only SDR that has an absolute dB calibration that I know of is the SDRplay, and that is only under certain conditions.
https://www.youtube.com/watch?v=MRR-x_TjOp4

This my test of the SDRplay calibration:

https://i.imgur.com/UHllVIm.jpg

I wasn't able to duplicate the artifact problem:

https://www.dropbox.com/s/mj126w9mt26uh0p/SDR%23%20v1.0.0.1732%20-%20AIRSPY%202020-09-07%2022-37-37.mp4?dl=0

https://www.dropbox.com/s/mj126w9mt26uh0p/SDR%23%20v1.0.0.1732%20-%20AIRSPY%202020-09-07%2022-37-37.mp4?dl=1

I notice that you have added the SNR meter plugin from GitHub. Did you have the artifact problem before you added the plugin?

Disregarding the curious ghost, does your R2 otherwise function properly?

Your R2 might be defective, or it could simply be a firmware issue.

We are both using the same software version, but since I bought my R2 first, the firmware version might be different. Airspy support would know what firmware version you have if they know what R2 you have.

There is a way for me to find out what firmware version I have, but I don't want to use a command prompt on my R2. Since my R2 seems to be working OK, I might mess it up.
AIRSPY R2 & MINI Software Defined Radio Firmware Update Procedure
https://www.youtube.com/watch?v=cMm7vC4gklA

Google search:
airspy R2 firmware

My Airspy R2 just bricked, no idea why...any suggestions for bringing it back?
https://www.reddit.com/r/RTLSDR/comments/dcy12p/my_airspy_r2_just_bricked_no_idea_whyany/
click on VIEW ENTIRE DISCUSSION for this:
melvin2204
RTL-SDR v3, Airspy Mini, R2, HF+ Discovery0 points ·
11 months ago
· edited 11 months ago

It's called 'The Ultimate VHF/UHF RX “Brick”' for a reason. Jokes aside, you might have more luck contacting @lambdaprog on Twitter. He partially runs Airspy.

level 2
byf_43
1 point ·
11 months ago

Haha, yeah I wasn't aware of that less than stellar reputation. I did get an initial email back from Airspy's customer service, but I have a feeling I won't have this up and running by tomorrow.

Do you have any suggestions for another SDR that might be more robust than the Airspy?


Adapter

Also -- I'm using a SMA <--> F adapter cable. So, no "hard" connection from the Airspy to the coax going on.
Good

[rabbit73]

This is interesting. Tablo support got back to me and indicated that the signal strength from my antenna may be too much for my Tablo. They recommended I turn my antenna away from the towers. I'm not entirely certain this is the correct course of action.

I asked if I could just put a splitter in-line to drop things if the signal is too strong. I went ahead and put in an Extreme BDS103H splitter with the -3.5dB output connected to the Tablo. I'm still receiving channels after performing a new scan so it didn't kill anything.

If that's not enough, and this truly is the problem, I can switch over to the -7dB port and see if that fixes things. I also have an Extreme BDS102H splitter that I assume I can daisy chain with the BDS103H for a max drop of -10.5dB.
That IS interesting. How did they know how strong your signals are, did you give them a signal report?
https://www.rabbitears.info/searchmap.php?request=result&study_id=143302

https://i.imgur.com/THktXAU.jpg

https://i.imgur.com/v3v6RWt.jpg

Turning the antenna away from the transmitter direction is one way to make signals weaker, but it tends to pick up multipath reflections which will increase errors. A better way is to use some type of an attenuator if you actually have signals too strong for a tuner. Longer coax or splitters will do fine.

WDAY RF 21, your strongest signal, would be the most likely signal to cause overload. But I never thought it would be a problem because you already have attenuation from the trees and the long coax when the antenna is outside. When the antenna is inside, you have even more attenuation.

A signal report is only a computer simulation which is often not very accurate, especially for 2Edge and Tropo signals. It assumes your antenna is in the clear, and doesn't account for coax loss.

So, it was a good idea to make the tests that you did to eliminate that possibility.

A rabbitears.info report lists a Signal Margin for a channel; it's similar to Noise Margin on a TVFool report.

https://i.imgur.com/aBX4bzt.jpg

Add the antenna gain and any preamp gain to the Signal Margin/Noise Margin when you look at the chart.

Interpreting Noise Margin in the TV Fool Report
http://www.aa6g.org/DTV/Reception/tvfool_nm.html

When you add an attenuator, it will make your strongest signal weaker, but it will also make your weakest signals even weaker by the same amount. If your weakest signals are already marginal, they could completely drop out.

When you have very strong signals and very weak signals, there is a great difference between the two. The difference between the strongest signal and the weakest signal is called the Dynamic Range, which is measured from the top of the strongest signal to the top of the weakest signal. To that, you must add 15 or 16 dB to allow for the necessary SNR of the weakest signal above the noise floor. This is called the SFDR (Spurious Free Dynamic Range.

Your goal is to make all the signals strong enough so that even the weakest can be decoded by the tuner, but not strong enough for the strongest signals to cause overload. Overload from two or more strong signals can create spurious signals from IMD (Intermodulation Distortion). The spurious signals will come up from the noise floor and reduce the SNR of the weakest signals.

https://i.imgur.com/BbBYEES.jpg

[rabbit73]

With a Tablo, the support folks apparently can log in remotely and check signals reported by the device itself. Unfortunately, this signal information is not exposed to end users.
Yes, unfortunate. If it had a GUI that gave that information, more peole would buy it.
I asked if it were possible to give me access to the insides and let me know what I need to target for signal levels. I doubt they'll go for it, but it never hurts to ask.
Indeed.

To give you a feeling for signal levels, here is your report in dBm:
https://www.rabbitears.info/searchmap.php?request=result&sort=field&unit=m&suppoff=N&sslimit=N&study_id=143302&opkey=C

https://i.imgur.com/JUW4dCl.jpg

And these are the specs by ATSC:

ATSC Recommended Practice:
Receiver Performance Guidelines

Document A/74:2010, 7 April 2010

RECEIVER PERFORMANCE GUIDELINES

5.1 Sensitivity

A DTV receiver should achieve a bit error rate in the transport stream of no worse than 3x10E-6 (i.e., the FCC Advisory Committee on Advanced Television Service, ACATS, Threshold of Visibility, TOV) for input RF signal levels directly to the tuner from –83 dBm (-34 dBmV) to –5 dBm (+44 dBmV)for both the VHF and UHF bands.

5.2 Multi-Signal Overload

The DTV receiver should accommodate more than one undesired, high-level, NSTC or DTV signal at its input, received from transmission facilities that are in close proximity to one another. For purposes of this guideline, it should be assumed that multiple signals, each approaching –8 dBm (+41 dBmV), will exist at the input of the receiver.

Presumably for Two Strong Input Signals.
Max Signal Input and Output
would need to be DERATED:
3 Signals: -3.6 dB
4 Signals: -5 dB
5 Signals: -6 dB
6 Signals: -7 dB
8 Signals: -8 dB
Ignore signals more than 6 dB below the Strongest.

So, you see that -22 dBm for WDAY even before adding the antenna gain is getting close to -8 dBm, which is why Tablo support was concerned.

Majortom and 905shmich have worked out a way to get more info from the HDHR GUI using Linux, but I'm satisfied with what it gives me already.

https://i.imgur.com/790A5WJ.jpg

https://i.imgur.com/Bl5m3Mv.jpg

The DHC forum software has changed; new link for that post:
https://www.digitalhome.ca/threads/hdhomerun-for-ota-discussion.191274/post-2478858

The signal strength never goes above 0 dBmV, no matter how strong it is, the Signal Quality never goes below 41, and the SNR never goes above 33.

I assume the same thing could be done with the Tablo.

[Tower Guy]

Overload can get very tricky. When calculating the cumulative level of multiple signals you add the peak voltages together (not the RMS) to get the peak voltage, and then calculate the peak power from the combined peak voltages.

For instance, the peak power of two signals of the same amplitude but different frequencies is 6 dB higher than one of the signals. It is this higher peak power that can overload the tuner.

[rabbit73]

Overload can get very tricky. When calculating the cumulative level of multiple signals you add the peak voltages together (not the RMS) to get the peak voltage, and then calculate the peak power from the combined peak voltages.

For instance, the peak power of two signals of the same amplitude but different frequencies is 6 dB higher than one of the signals. It is this higher peak power that can overload the tuner.
Good point.

I would hope that the engineers that wrote the ATSC specs took that into consideration, but maybe they didn't.

This part was added by holl_ands, who does modeling and is an RF engineer, so I took it on faith because I'm not smart enough to verify it:

Presumably for Two Strong Input Signals.
Max Signal Input and Output
would need to be DERATED:
3 Signals: -3.6 dB
4 Signals: -5 dB
5 Signals: -6 dB
6 Signals: -7 dB
8 Signals: -8 dB
Ignore signals more than 6 dB below the Strongest.

The rabbitears.info report is only a computer prediction, but we see the reality in the spectrum scan done by verder. Unfortunately, the dBm calibration is not absolute, but we can see the relative powers of the channels. He would need a signal level meter to measure the actual powers of the channels.

https://i.imgur.com/v3v6RWt.jpg

https://i.imgur.com/JUW4dCl.jpg

The power level of WDAY implied by the scan and shown in the signal report looks like it is close to the limit that could be tolerated by the tuner.

Verder gave me his address in a PM, so I was able to look at the satellite vertical view that shows trees in the signal paths from both directions that would attenuate the signals. I was also able to look at the ground photos that confirmed the trees were higher than the antenna, but he asked me not to show those images in this thread.

That's what led me to the conclusion that overload was probably not a threat unless he added a high gain preamp. I think that the intermittent pixelation that he has on the marginal channels is not from fundamental overload or IMD spurs, but from insufficient SNR of the weak signals and multipath from the signals passing through the trees. Both of those can produce errors that exceed what the FEC can correct.

This is what a signal looks like when it is going through trees on a very windy day:

https://www.dropbox.com/s/ig3va499k237ayu/CH16TreeInPath4.mp4?dl=0

https://www.dropbox.com/s/ig3va499k237ayu/CH16TreeInPath4.mp4?dl=1

In any event, verder made the correct test by adding attenuation which showed that the pixelation continued, so it probably isn't caused by overload.

A more certain test would require a single-channel custom filter that would attenuate WDAY, but that would be expensive.

[rabbit73]

I'm going to show my ignorance here because I don't fully understand what you were pointing out with your last post. You say "you see that -22 dBm for WDAY before adding the antenna gain is getting close to -8 dBm". I don't understand (intuitively) how these are close. Given that dBm is a logarithmic scale, aren't these relatively far apart?
I owe you an apology. I have been dumping a lot of technical information on you without knowing your background, but you seemed to be interested in learning more.

I should have shown the math to support my statement.
I'm at a loss (ha!) at how to correlate from the antenna gain to the levels you point out from the ATSC requirements. The 4Max has these specs: "UHF 11 dBi / VHF 2.5 dBi". If WDAY (ideally) has a signal power of -22dBm, then how does the antenna gain affect what is ultimately fed into the tuner? It's not as simple as adding the two values is it? 11dBi + (-22dBm) = -11dBm? That's getting somewhat close (3dB), but I think I'm horribly conflating things at this point.

https://i.imgur.com/0Rt3JPz.jpg

It is pretty much that simple. I'm used to using the TVFool reports where Noise Margin (NM) 0 dB is for a dipole antenna. The strength of a signal is shown in two ways on a TVFool report: NM or Signal Power. You can add antenna gain to either one. See this FAQ:
https://www.tvfool.com/?option=com_content&task=view&id=57
Antenna gain is the only quantity that should ever be ADDed to the NM value. Most antennas will specify their gain in dBd or simply dB, and this is the value that should be used. If an antenna's gain is specified in dBi units, then you need to subtract 2.15 in order to get the equivalent value in dBd units.

More recently, the TVFool reports have become less accurate because they use a database with many errors to generate reports. Trip (Trip in VA on the AVS Forum), who is the webmaster for rabbitears.info and now works for the FCC, decided to create the Signal Search Map to generate reports. Trip asked me to be a beta tester, so I was able to make a few comments that I hoped were useful.

The rabbitears reports are now our first choice and I assume I can also add the antenna gain to the dBm value or the Signal Margin value.

https://i.imgur.com/JUW4dCl.jpg

Antenna gain 11 dBi - 2.15 = 8.85 dBd (in reference to a dipole)

WDAY -22 dBm + 8.85 dBd = -13.15 dBm, which is weaker than -8 dBm
I don't quite understand what the multi-signal overload text is stating. Is it saying the more strong signals you have, the more you need to derate these strong signals, and the recommended amounts they need to be derated at? 8 strong signals = derate by 8dB, because otherwise the tuner is overloaded?
The ATSC Guideline says that a tuner should be able to tolerate a signal as strong as -5 dBm. Where there are multiple signals, the tuner should be able to tolerate them if they are no stronger than -8 dBm, which is weaker because we are in negative values.

The derating chart after that is not part of the ATSC Guidelines. It came from holl_ands who is a member of the AVS and DHC forums, is an RF engineer, and does antenna computer modeling. The derating chart says that the signals must be even weaker if you have more of them.

Does all of this come together to indicate that maybe it would have been better if I had gone with the ClearStream 2Max instead? It has the specs: "UHF 8.7 dBi / VHF 2.6 dBi". All of this of course assumes that the signals are indeed too strong for the Tablo.
The CS 2MAX does have less gain than the CS 4MAX, so there is less chance of overload if that really is a problem with the Tablo. The advantage of the CS 2MAX for you is its wider beamwidth because your two directions are not 180 degrees apart. I have heard reports that the TiVo and HDHR don't tolerate strong signals as well as the average TV tuner, but I haven't made any tests to confirm that.

I have made overload tests on tuners. The first one I did was from ignorance. I connected two preamps in series because I thought more gain is better; I didn't get any signals at all.

The more informed tests that I made later showed that the strongest signals created IMD (Intermodulation Distortion) products called spurious signals (spurs) that wiped out the weakest signals. As I increased the gain even more, only the strongest signals were left, and finally even they were gone. I was working in the range of -5 to +5 dBm. I didn't want to go any higher because it might damage my tuner.

THREE TYPES OF OVERLOAD

There are three types of preamp or tuner overload, in order of increasing signal strength:

1. The strong signals almost cause enough intermodulation distortion (IMD) to interfere with the reception of weak desired signals, but the spurious signals are at or below the noise floor of the weak signals. This is the point that holl_ands uses in his preamp charts to obtain max SFDR (Spurious Free Dynamic Range). No damage will happen.

As the strongest signals continue to increase in strength, more of the weaker signals are damaged until you reach:

2. The strong signals cause overload to the preamp or tuner that makes it impossible to receive any signals. No damage will happen. The strongest signals are still there, but they can't be decoded because the IMD products have damaged them so that they contain more errors (high BER....bit error ratio/rate) than can be corrected by the FEC (forward error correction).

3. The signals are so strong that the input transistor is toast. You are not likely to encounter OTA signals that strong, unless you live next door to a high power transmitter and you have your high gain antenna aimed at the transmitter's antenna.

As a general rule, tuners can tolerate stronger signals than preamps before overload. The difference in strength is approx. equal to the preamp gain.

[rabbit73]

I ran the RG6 to a cheap MediaSonic digital tuner I picked up from Amazon that was connected to a TV via HDMI. I used that to get a rough signal quality reading and also would watch one channel on each carrier frequency for a minute or two to look for drop-outs or pixelation.
You asked in the thread about Tablo vs the TV tuner. I've only really used the TV tuner to do the original setup (finding the sweet spot.) From that point it's been pretty much using the Tablo exclusively. I have not used the MediaSonic TV tuner for an extended period of time.
That said, I'll do some experimentation and some longer viewing with it on the channels I've had issues with to see if there's anything unique with that (drop-outs or what-have-you.) Thankfully the Tablo has been recording what station, day, and times the problems are occurring. I'm starting to record that info in a spreadsheet to see if I can see a pattern or anything emerge.
I'm considering getting either a cheap HDHomeRun or perhaps a Hauppauge TV tuner. These include signal meter, signal quality, and symbol quality information that are provided by GUIs / phone apps. Curious if others out there have gone this route and what signal information they've been able to use to their advantage.
Unfortunately, the Gray-Hoverman frame turned out to be too big for my rafters, so I switched over to the Mclapp. I used a 50' dual-shield RG6 coax line to run from my rafters to a splitter on my workbench. The splitter feeds 2x identical Dynex TVs. One was set to the internal digital tuner and the other was connected to a cheap MediaSonic digital tuner via HDMI input. The Dynex TVs have a "Channel Strength" reading and the MediaSonic has a "Quality" reading that I referenced.
It turns out that Channel Strength and Quality don't amount to much. In the rafters with the antenna pointed towards the northwest towers, I'd have "Good" (highest Dynex reading) and would see pixelation / drop-out. With the MediaSonic quality almost always about 50%, I'd see it drop-out down to 0% (signal loss).
Unfortunately, I do not own an HDHomeRun yet so I don't have access to that additional signal information.
Your comments about the Mediasonic converter box made we wonder about how it would compare with the HDHR at weak-signal dropout.

Tyler the Antenna Man did two reviews about converter boxes, the Mediasonic Homeworx HW-150PVR and the Ematic AT103B:
Mediasonic Homeworx DTV Box with DVR Review - Record OTA Antenna TV
May 14, 2020
https://www.youtube.com/watch?v=6LO7h1YIMv4

Ematic AT103B Digital Converter Box + DVR Recording Tutorial & Review
Dec 21, 2018
https://www.youtube.com/watch?v=a9KUAjjcDww

The GUI for the Mediasonic looks a lot like the GUI for the Channel Master 7003. I have a 7003, so I compared it with my HDHR4-2US using a variable attenuator and a splitter on my best channel (RF 16). I increased the attenuation to bring it down to dropout for the 7003:


7003 > TV
/
Ant > Variable 0-10dB > Fixed 20dB > Splitter
Attenuator Attenuator \
HDHR > Laptop


https://i.imgur.com/JHv7YCf.jpg

https://i.imgur.com/hlLJWkv.jpg

The variable attenuator was set at 6 dB, so the margin to dropout for the 7003 was 26 dB for channel 16. The signal quality varied from 39 to 41%. The HDHR tuner was a little more sensitive; margin to dropout was about 28 dB.

Using a converter box and a variable attenuator is almost a useful as the critical 50% signal quality point of the HDHR.

I found this on eBay; had to add BNC to F adapters:

https://i.imgur.com/9oR7Ke3.jpg

I have some fixed attenuators like this; they can be stacked
1-3dB
1-6dB
1-10dB
2-20dB

https://i.imgur.com/YJjEWvo.jpg

https://mjsales.net/products/fam-attenuator?variant=1083705673

https://www.newark.com/webapp/wcs/stores/servlet/Search?storeId=10194&catalogId=15003&langId=-1&categoryId=800000004899&mf=106654

[rabbit73]

When digital TV arrived, I was looking for an inexpensive way to measure the strength of digital TV signals. Signal level meters are made for the task, but they cost more than most people want to spend.

I found this UK site that showed how to use inexpensive attenuators to make comparative signal strength measurements of digital TV signals using the concept of margin to dropout. It's the same link as in my signature:
http://www.me galithia.com/elect/aerialsite/dttpoorman.html (http://www.megalithia.com/elect/aerialsite/dttpoorman.html)

I found two Channel Master slide-switch attenuators, each with a 3dB, 6dB, and 12dB switch. With the proper settings I was able to get 0, 3, 6, 9, 12, 15, 18, or 21 dB for each attenuator; the total for both was 42dB.

https://i.imgur.com/Hlyej14.jpg

The next device I found was the Apex DT502 converter box. It has two scales, one for signal quality and the other for signal strength.

https://i.imgur.com/hyELmEv.jpg

Using my attenuators I was able to get readings for a channel as I brought it down to dropout. Obviously, the greater amount of attenuation needed to bring the channel to dropout, the stronger the signal. Since dropout is at about -85 dBm for most tuners, I was able to calculate the strength of the signal by adding the attenuation to -85 dBm.

https://i.imgur.com/YyegW9v.jpg

https://i.imgur.com/69pxTA6.jpg

Later, if I wanted to compare my calculated strength with a measured strength, I could use my Sadelco 719E signal level meter. Once I knew the strength in dBmV, I could convert it to dBm by subtracting 48.8:

https://i.imgur.com/enUFXCQ.jpg

and I was also able to calibrate the DT502 signal strength scale:

https://i.imgur.com/qBCt9cO.jpg

You can do the same thing with just your TV tuner. Bring the signal to dropout with an attenuator and add the attenuation needed to -85 dBm; that is the strength of the signal. This is most accurate on UHF. On VHF, the noise level is higher, so dropout will be above -85 dBm.

[tripelo]

...
When you have very strong signals and very weak signals, there is a great difference between the two. The difference between the strongest signal and the weakest signal is called the Dynamic Range...


This topic probably could be in another thread.

Would like your thoughts on dynamic range of Airspy vs. SDRplay RSP1.

Rabbit73, do you see differences in instantaneous dynamic between the two scanners, for:

- Wideband (several channels displayed)
- Single channel (display maybe 8-10 MHz or so)

No hurry on response. Do not wish to derail current thread.

Thanks

[Tower Guy]

This part was added by holl_ands, who does modeling and is an RF engineer, so I took it on faith because I'm not smart enough to verify it:


Holland’s is correct, but note that he started with two signals already, so add 6 dB to his numbers to get the Peak power ratio to a single signal.

[rabbit73]

This topic probably could be in another thread.

Would like your thoughts on dynamic range of Airspy vs. SDRplay RSP1.

Rabbit73, do you see differences in instantaneous dynamic between the two scanners, for:

- Wideband (several channels displayed)
- Single channel (display maybe 8-10 MHz or so)

No hurry on response. Do not wish to derail current thread.

Thanks
Good to hear from you.

The OP and I are both interested in SDRs as a diagnostic tool. I see no harm in a brief response.

The dynamic range of the SDR is determined by the bit depth of the ADC (Analog to Digital Converter). The Airspy R2 and SDRplay RSP1A are very similar in that respect; 12 bits. Both are far superior to the RTL-SDR.COM V3 dongle which has an 8 bit depth ADC, giving it a dynamic range of about 50 dB. Comparison chart here:
Comparisons with other common Wideband Commercial Software Defined Radios
https://www.rtl-sdr.com/about-rtl-sdr/

For a scan of 8-10 MHz for a single channel, both are quite rapid. For a wider scan, it takes slightly longer as would be expected, but it is real-time that can show changes. The Spectrum Spy scanner is faster than the SDRplay scanner. Both scanners are much more rapid than the RTL-SDR Scanner which takes forever to piece together individual sections into a complete scan; not real-time.

The separate scanner software available for the RSP1A looks like an old-time SA. The Spectrum Spy software that is included in the SDR# download for the R2 is very colorful. I prefer it to the scanner for the RSP1A, but the R2 costs twice as much as the RSP1A.

Some videos
Channels are 16, 19-21, 31-33, cellular

Scanner for RSP1A

still

https://i.imgur.com/ZEudnsx.jpg

https://www.dropbox.com/s/xdysaeqzc3wvppd/RSP%20Spectrum%20Analyser%20-%20V3.xx%20API%20Test%20version%202020-09-11%2013-27-59.mp4?dl=0

https://www.dropbox.com/s/xdysaeqzc3wvppd/RSP%20Spectrum%20Analyser%20-%20V3.xx%20API%20Test%20version%202020-09-11%2013-27-59.mp4?dl=1

hide controls

https://www.dropbox.com/s/nl1876xejjn9upa/RSP%20Spectrum%20Analyser%20-%20V3.xx%20API%20Test%20version%202020-09-11%2013-32-41.mp4?dl=0

https://www.dropbox.com/s/nl1876xejjn9upa/RSP%20Spectrum%20Analyser%20-%20V3.xx%20API%20Test%20version%202020-09-11%2013-32-41.mp4?dl=1

Spectrum Spy for R2

still

https://i.imgur.com/xHTWPh5.jpg

https://www.dropbox.com/s/gars272disx2t4z/Spectrum%20Spy%202020-09-11%2014-12-56.mp4?dl=0

https://www.dropbox.com/s/gars272disx2t4z/Spectrum%20Spy%202020-09-11%2014-12-56.mp4?dl=1

[rabbit73]

Holland’s is correct, but note that he started with two signals already, so add 6 dB to his numbers to get the Peak power ratio to a single signal.
Thank you.
73

post by majortom about 1/4 wave stubs
use 7th harmonic
https://www.digitalhome.ca/threads/on-hamilton-stoney-creek-brantford-haldimand.36535/post-3109007

[rabbit73]

I keep checking to see if I can post directly to the reply. I still cannot. :(

I actually picked up the MediaSonic tuner as a result of watching Tyler the Antenna Man's youtube video. The signal quality display view is identical to your CM7003 converter box.

When I had dropout on the MediaSonic, the quality was easily 70% or so. Then, it would go to 0% and lose signal, then come back and be back in the 70% range again. So, using that a measure of performance wasn't all that useful.
The Mediasonic is telling you the truth.

When it goes to 0% signal quality, there are more errors than the FEC (Forward Error Correction) is able to correct. The FEC has a limit to its ability to correct errors.

When it comes back to the 70% range, there are no uncorrected errors.

If you had an HDHR, it would show a green Symbol Quality bar at 100% when there was 70% signal quality on the Mediasonic.

The HDHR Symbol Quality bar would be red at the times when the Mediasonic was going to 0%.

The increase in errors is most likely from the signal passing through the trees. You will continue to have multipath dropouts as long as there are trees in the signal path.

The same thing is happening to me because there is a tree in front of my antenna; it's worse with my weakest channels.

https://www.dropbox.com/s/q79o3x433hjsg1w/HDHomeRun%20Config%20GUI%202020-09-11%2019-41-08.mp4?dl=0

https://www.dropbox.com/s/q79o3x433hjsg1w/HDHomeRun%20Config%20GUI%202020-09-11%2019-41-08.mp4?dl=1

[rabbit73]

Support indicates that KRDK and WDAY are still coming in too strong.
You tried an attenuator, and it didn't help with the ghost artifact or dropouts, did it? You could try more attenuation.
They also recommended using an LTE filter. I actually have one and used it previously but it did not work. I put it back in-line and also moved to the -7dB output of the BDS103H (previously I was on the -3.5dB output.)
There are two CM LTE filters with the same model number CM-3201. You would need the newer 600 MHz LTE filter if your cellular signals were strong enough to cause interference, but they don't look that strong in your scan.

https://i.imgur.com/UfT7GDN.jpg

https://i.imgur.com/iTqlYVK.jpg

I also mentioned that the back and forth with support since I have no access to the tuner's quality measures is a pain. I brought up that the HDHomeRun provides this information and it is disappointing that the Tablo doesn't expose this info. Further, my request for 'inside' access to the Tablo went completely ignored. No surprise, but equally disappointing.

In other news, I've gotten absolutely no where with the US distributor of the Airspy R2. They wanted to pawn me off to community support since I had already tried everything they could think of. I pushed back and they directed me to contact Airspy HQ directly. If I don't hear back from them, I plan to contact my credit card company and see if they can rattle their cage. Granted it's only been two days since I e-mailed Airspy HQ, but I haven't even gotten an acknowledgement yet that they received my request so I have my doubts.
Two examples of poor customer support; typical performance for these times. Good customer support would cost them money; the bottom line is more important than the customer.

Their first line of defense is that the problem must be your fault. The current form of capitalism is heartless.

Can you use your Airspy R2 now for scans?

Did you try removing the GitHub SNR meter plugin?

Did you try a new download of SDR# after removing the old one?

There is a strong FM signal coming from the NNW. It's only 7 kW, but it's 1 mi away.
http://www.fmfool.com/modeling/tmp/9e241cfd4c/Radar-FM.png

Makes me wonder about FM interference.

[rabbit73]

I forgot to mention that I *know* the splitter is doing something. After I moved to the -7dB output and rescanned on the Tablo, K28MA is now showing up as 3 Orange dots rather than 5 Green dots for signal strength. Everything else is 5. Thankfully, K28MA is a duplicate of KXJB so I'm not really concerned here.

A quick < 1 minute view of all the XX-1 channels shows that they are at least coming in. No clue if they suffer from any dropout or pixelation issues.
That tells you the attenuator is making the signals weaker, but you don't yet know if reducing the signal strength reduces the dropouts and pixelation.

[tripelo]

...

The dynamic range of the SDR is determined by the bit depth of the ADC (Analog to Digital Converter). The Airspy R2 and SDRplay RSP1A are very similar in that respect; 12 bits. Both are far superior to the RTL-SDR.COM V3 dongle which has an 8 bit depth ADC, giving it a dynamic range of about 50 dB...

Yes, thanks for your response & images/videos.

As you imply above, for a particular bandwidth,
the number of bits in A/D converter set a limit on dynamic range.

In addition,
linearity of preceding preamplifier & mixers can degrade dynamic range from that of A/D converter alone.

Possibly your received signals are not strong enough to stress the linearity of the RTL front end.

When you have the scanners them properly adjusted, have you seen any spurs in either scanner?

----------------------

Your images and videos are informative.

Good to see a comparison of both scanners displays.

Reading the scale looks like about 60+ dB dynamic range displaying those particular signals.

Have you checked the accuracy of the dB scale?

Is there a means in software to calibrate the dB scale against a reference?

Wonder, when calibrated at one or two points, if it maintains some accuracy over a larger range of dB?

Do you think one of the two scanners could be more accurate than the other?

Thanks

[rabbit73]

When you have the scanners them properly adjusted, have you seen any spurs in either scanner?
There appears to be spurs in all three of my scanners, but it's not unexpected in equipment that isn't lab grade. I would need a pure source to really tell the spurs from actual signals.

The RTL-SDR dongle has a lot of spurs when I put a 75 ohm termination resistor on the front end, but they are minimized when signals are measured.

https://i.imgur.com/hQXDtBd.jpg

I think the Spectrum Spy scanner for the R2 is a lot cleaner than the RSP Spectrum Analyzer for the RSP1A.

Your images and videos are informative.

Good to see a comparison of both scanners displays.
Thank you. I was curious to make the comparison myself.
Reading the scale looks like about 60+ dB dynamic range displaying those particular signals.
A 12 bit ADC should be able to do at least a 60 dB dynamic range.
Have you checked the accuracy of the dB scale?
The dB scales on my three SDRs are relative, not absolute. There is one exception, the calibration of the RSP1A with the SDRuno software is calibrated under certain conditions:

SDRplay RSP2 for accurate RF power Measurement
https://www.youtube.com/watch?v=MRR-x_TjOp4

https://i.imgur.com/mLk6ABV.jpg

This is my test of the SDRplay calibration:

https://i.imgur.com/UHllVIm.jpg

I have used that feature to measure the strength of TV signals, but a correction factor of about +14 dB is needed:

Measuring TV Signal Strength with an SDR
https://www.avsforum.com/threads/the-official-avs-antenna-and-related-hardware-topic.381623/post-59870798

Is there a means in software to calibrate the dB scale against a reference?I think there are offset adjustments for the relative scale, but I haven't hunted for them because the position of the signal changes with adjustments of gain and display.

I think the calibration feature of the SDRuno mentioned above is fixed in the hardware or firmware.

Wonder, when calibrated at one or two points, if it maintains some accuracy over a larger range of dB?I have not tested the linearity of the relative dB scales. The accuracy of the "use under certain conditions" calibration of the SDRuno with RSP1A SDR appears to hold well over a wide range.
Do you think one of the two scanners could be more accurate than the other?I don't think the relative scales of either one could be considered "accurate" with so many stages in series.

[rabbit73]

I am working on a method of measuring the strength of a TV signal using only the TV tuner and an attenuator. It should help verder to be able to measure the strength of his strongest signal which seems to be in question.

I will also do some SDR accuracy measurements at the same time which should be of interest to tripelo.

I need some sleep now.

[tripelo]

There appears to be spurs in all three of my scanners, but it's not unexpected in equipment that isn't lab grade. ...

Yes.

The RTL-SDR dongle has a lot of spurs ...

Have noticed that in the low cost RTL devices. Most of the time not a problem if one is aware of their presence.


...I think the Spectrum Spy scanner for the R2 is a lot cleaner than the RSP Spectrum Analyzer for the RSP1A...

Interesting.

..The dB scales on my three SDRs are relative, not absolute.

Yes, the unit of dB itself is relative.

When uses as dBm or dB(other), then it takes on more absolute meaning.

-------------------

Curious about scale accuracy, sorta related to scale linearity:

Is a dB indicated, an actual dB.

For example:

Is a -20dB indication really 10dB less than a -10dB indication? Or,

Is the delta, 9 or 11 dB or some other number.

-------------------

...I think there are offset adjustments for the relative scale,...

....I don't think the relative scales of either one could be considered "accurate" with so many stages in series.

Thanks for the information and the images, helps to better understand these interesting devices.

.

[rabbit73]

Here is an example of using an attenuator to measure the strength of a digital TV signal. I picked RF channel 20 to measure.

https://i.imgur.com/IVd22XT.jpg

This is my signal report in dBm:
https://www.rabbitears.info/searchmap.php?request=result&sort=field&unit=m&suppoff=N&sslimit=N&study_id=145947&opkey=C

https://i.imgur.com/jua41AY.jpg

This was my setup:


TV for SNR
0 to 10 dB /
Ant > 25ft RG6 > Attenuator > A/B Switch
at 0 dB \
Meter or SDR

The Sadelco DisplayMax 800 signal level meter reading was -7.3 dBmV = -56.1 dBm

I added attenuation, for a total of 30 dB, to bring the signal down to 15 dB SNR at the "Digital Cliff."


TV for SNR
0 to 10 dB Fixed /
Ant > 25ft RG6 > Attenuator > Attenuators > A/B Switch
at 7 dB 20+3 dB \
Meter or SDR


This is what the scan looked like at dropout. Note that I had to increase the SDR gain for the proper display:

https://i.imgur.com/3krBkIX.jpg

So, to calculate the signal strength, the basic rule says to add the amount of attenuation needed for dropout to -85 dBm, which is the average dropout point of a tuner:
-85 dBm + 30 dB = -55 dBm

The signal level meter reading for the signal was -56.1 dBm; close enough for a good estimate to determine the signal strength.

The 30 dB of attenuation needed to bring the signal down to 15 dB SNR is sometimes called Margin to Dropout.

Channel 20 is listed at -26 dBm on my report. The trees are causing a lot of signal loss.

Note that I really only needed the TV and the attenuator to determine the signal strength. I added the SDR and the signal level meter to verify the method.

[rabbit73]

Curious about scale accuracy, sorta related to scale linearity:

Is a dB indicated, an actual dB.
The only dB scale on an SDR that I have confidence in is the dBm calibrated scale for the RSP1a with SDRuno software. I used it during the above test.

https://i.imgur.com/I2S4W8l.jpg

https://i.imgur.com/R6JVmCl.jpg

https://i.imgur.com/VYu7lqo.jpg

https://i.imgur.com/GiahYDw.jpg

I couldn't figure out a way to get a direct reading of the signal power as shown in the YouTube video or with my NTSC modulator, so I had to settle for using a correction factor. It's probably measurement-bandwidth related.

Correction factor
99.5 - 85 = 14.5
-70.1 dBm + 14.5 = -55.6 dBm

Regarding linearity:
The signal does appear to be about 30 dB weaker at dropout on the calibrated dBm scale AND the relative dB scale.

With a flat signal, the placement of the measurement window isn't very critical, but with a signal that doesn't have a flat top, it's up to you to place it at an average level point.

This is the way my signal level meter does it, and takes the average:

https://i.imgur.com/sLPqJdr.jpg

[tripelo]

The only dB scale on an SDR that I have confidence in is the dBm calibrated scale for the RSP1a with SDRuno software....

Thanks.

That is quite a difference between your calibrated RSP1a and the Airspy.

.

[rabbit73]

Can you use your Airspy R2 now for scans?

Did you try removing the GitHub SNR meter plugin?

Did you try a new download of SDR# after removing the old one?


It still functions. I get ghost spikes now is the problem.

SNR meter plugin is a non-issue. As mentioned previously, the ghost spikes occur on completely separate machines with their own installs of the latest SDR# (and those did not use the plugin.)

If it's FM interference, then it's a mystery why I didn't see this for the first two weeks or so of owning the device. I've done a bit of messing around with trunked voice comms and never saw this issue.
Thank you for your reply.

[rabbit73]

As of this morning I still get weak signal reports (recording failed @ 1am). Current setup:

antenna input > cm3201 > splitter/7dB drop > tablo

I have the newer CM3201.

We watched a football game yesterday on the same channel (KVRR) as this morning's failed recording and didn't notice any issues except for maybe one short ~1 second occurrence that had digital smearing. I believe the weather was clear overnight.

I'm currently waiting for Tablo support to get back to me in this continuing saga of e-mail tag. I learned that they send your case to the back of the line every time you update them with new info via email. I guess it pays to be quiet. :P
I hope that they will take your request seriously enough to give you some useful help.
I have half a mind at this point to get a ClearStream 2Max and replace the 4Max. Wondering if the wider beamwidth will help with KVRR reception or what.
The CS 2MAX does have a wider beamwidth but a little less gain. Difficult to predict the results of a test.

We are now at post #55 on your thread and I'm running out of ideas. I've learned a lot trying to help you and have had a chance to show off some of my ideas about SDRs and how to measure the strength of a TV signal without a signal level meter.

I keep picturing your antenna above the trees, but I know that isn't going to happen.

If you went to AVS, Calaveras would probably say get your antenna above the trees.

Example of Vegetation Affecting Signal Strengths-Part 1
https://www.avsforum.com/threads/example-of-vegetation-affecting-signal-strengths-part-1.2005866/

[rabbit73]

I was wondering why Tablo support thinks your signals are too strong. This seems to answer the question:
Getting Technical with Over-the-Air TV Reception (AKA: Why Can’t I Watch This Channel?)
https://www.tablotv.com/blog/getting-technical-over-air-tv-reception/

https://i.imgur.com/HhjS5EH.jpg

A GOOD tuner should be able to receive signals much stronger than -50 dBm. Apparently, the Tablo tuners don't meet the ATSC specs:

ATSC Recommended Practice:
Receiver Performance Guidelines

Document A/74:2010, 7 April 2010

RECEIVER PERFORMANCE GUIDELINES

5.1 Sensitivity

A DTV receiver should achieve a bit error rate in the transport stream of no worse than 3x10E-6 (i.e., the FCC Advisory Committee on Advanced Television Service, ACATS, Threshold of Visibility, TOV) for input RF signal levels directly to the tuner from –83 dBm (-34 dBmV) to –5 dBm (+44 dBmV)for both the VHF and UHF bands.

-50 dBm + 49 = -1 dBmV

Cable guys want you to have at least that much signal at the wall plate for your TV.

Maybe they got the idea from SiliconDust. 100% on the HDHR GUI is only one dB more at 0 dBmV.

Most of my Sony TVs say MAX or 100 at 0 dBmV except for one model that goes much higher:

https://i.imgur.com/USrn73K.jpg

[rabbit73]

I appreciate the time you've put into this so far! I'm learning quite a bit in the process.

I find this comment from Calaveras very telling:


Even though the signals look strong enough to receive, only 2 out of 9 stations will decode with the antennas lowered and their SNRs are very low due to severe multipath.


Without elevating things above the tree-line, I'm thinking this is as good as things are going to get for me. A CS2M may help out with KVRR reception... I'd most likely remove the splitter or go back to the -3.5dB output in that case. If it does, I could probably donate my CS4M to my father-in-law who lives out in the country and relies on an el-cheapo mudflap for his OTA reception. So, it wouldn't be a total loss.
That sounds like a good plan.

[verder]

My account has finally been activated. I PM'd the "admin" user and was approved last night I guess. Cue this clip! (https://www.youtube.com/watch?v=-7aIf1YnbbU) :)

[rabbit73]

My account has finally been activated. I PM'd the "admin" user and was approved last night I guess.
Congratulations!

A little late, but they finally got to you.

Cue this clip! (https://www.youtube.com/watch?v=-7aIf1YnbbU) :)
For the moment you get excited about whatever makes you "somebody." (Steve Martin; from the 1979 movie The Jerk).


Ha Ha, that's a good one.:)

Welcome, verder; you are now "somebody" on the TVFool website.

[eclipsme]

Welcome. I have been following along, picking up a few things along the way.
Congrats!

[rabbit73]

Using an Attenuator to Measure the Strength of a Digital TV Signal, Part 2

I ordered a Mediasonic HW-150PVR and a Toner 0-20 dB Variable Attenuator to see how they would do at estimating the strength of a TV signal.

I had previously used a 0-10 dB step attenuator, but they are expensive; I was lucky to find a good used one. I'm trying to find the least expensive equipment to do the job.

I had also used an Antennas Direct 0-20 dB Variable Attenuator, but they have been discontinued along with their FM filter.

http://forum.tvfool.com/attachment.php?attachmentid=3880&d=1600732690

http://forum.tvfool.com/attachment.php?attachmentid=3881&d=1600739602

http://forum.tvfool.com/attachment.php?attachmentid=3882&d=1600740885

http://forum.tvfool.com/attachment.php?attachmentid=3887&d=1600797177

Since the AD ATT-1 was no longer available for others to buy, I made a calibration chart for the Toner attenuator:

http://forum.tvfool.com/attachment.php?attachmentid=3875&d=1600708146

I don't know why the factory pasted the label on upside down.

I put a black mark on the knob and on the housing to be able to count the number of turns as I rotated the shaft counterclockwise with a screwdriver to increase the attenuation to dropout.

http://forum.tvfool.com/attachment.php?attachmentid=3876&d=1600711501

This was the setup:



Fixed Variable SDR
Ant > 25 ft RG6 > Attenuator > Attenuator > 4-Way Splitter > HW-150
20 dB at 1-1/2 turns SLM*
5 dB 75 ohm terminator
* SLM is Sadelco DisplayMax 800 Signal Level Meter


http://forum.tvfool.com/attachment.php?attachmentid=3877&d=1600712295

To find the signal strength of Channel 20, I added the attenuator setting to the average tuner dropout point of -85 dBm:
-85dBm + 25 dB = -60 dBm

To confirm the method, my Sadelco DisplayMax Signal level meter reading was -11.9 dBmV = -60.7 dBm

(Since I used a 4-Way splitter, the signal before the splitter was 7 dB stronger. I put a 75 Ohm terminator on the unused port because without it, the outputs weren't equal.)

This method works best on UHF. On VHF, where the noise level is higher, dropout will be higher than at -85 dBm.

http://forum.tvfool.com/attachment.php?attachmentid=3879&d=1600731992

The Thermal Noise Floor for a 6 MHz wide TV signal is about -106 dBm.

The Noise Figure for the average tuner is 6 dB:
-106 dBm + 6 dB = -100 dBm

To that we must add 15 dB to allow for the minimum required SNR for the TV signal:
-100 dBm + 15 dB = -85 dBm

However, if the ambient noise is stronger than the internal noise of the tuner, the tuner Noise will be buried in the ambient noise.

[rabbit73]

Review of Toner 0-20 dB Variable Attenuator

I ordered two of the Toner attenuators in case one was defective. One of them had a coax connector with insulation that hadn't been completely removed, making it difficult to insert the center conductor of the RG6 coax.

http://forum.tvfool.com/attachment.php?attachmentid=3893&d=1601157632

http://forum.tvfool.com/attachment.php?attachmentid=3894&d=1601157649

I removed the excess insulation with a drill bit held in my hand; the coax was then able to be properly inserted.

I still haven't figured out why they would paste the label on upside down.

http://forum.tvfool.com/attachment.php?attachmentid=3895&d=1601157668

It's important to check the female coax connectors to see if they make good contact with the center conductor of the coax:

http://forum.tvfool.com/attachment.php?attachmentid=3896&d=1601157695

http://forum.tvfool.com/attachment.php?attachmentid=2816&d=1501113567

http://forum.tvfool.com/attachment.php?attachmentid=2817&d=1501113723

http://forum.tvfool.com/attachment.php?attachmentid=3897&d=1601159621

[rabbit73]

Would like your thoughts on dynamic range of Airspy vs. SDRplay RSP1.

Thanks
I did some additional tests with the SDRplay RSP1A and the RSP Spectrum Analyser (British spelling) software.

It seems that it is necessary to properly set the Reference level of the RSP Spectrum Analyser. If you set it too high, part or all of the signal will be buried in the noise.

The RSP Spectrum Analyser tries to simulate what a real spectrum analyzer does. You have to be careful with the Display scaling settings to get a correct representation of SNR. Manual:
https://www.sdrplay.com/docs/RSP-SpectrumAnalyser-V1.1.pdf

Setting RSP Spectrum Analyser Reference Level

Reference Level

A common error is a complaint that signals with a 40-50 dB SNR as displayed on SDRuno, shows a signal barely breaking through the noise floor on the analyser. In almost all cases, AGC is enabled on SDRuno, and the LNA gain reduction slider set at a low gain reduction value resulting in a lower noise floor. IF gain reduction will be whatever the AGC system sets it at.

Conversely, the analyser is usually set at a high reference level of somewhere between -30 to+10 dBm, has a very high noise floor and sees little or no signal above the noise. This is usually caused by the user attempting to use the reference level control to position the trace within the display area, instead of using the range and offset controls provided for this purpose.

The reference level should initially be set to around -80 dBm, while ensuring the ADC is not overloaded and spurious signals are not generated. This will give maximum sensitivity and a lower noise floor. Increasing the reference level towards 0 dBm will result in an increasing noise floor, and depending on signal level, may result a lower S/N ratio. Use the range and offset controls to scale and position the display as required.

An example:

http://forum.tvfool.com/attachment.php?attachmentid=3928&d=1603134499

http://forum.tvfool.com/attachment.php?attachmentid=3929&d=1603134556

http://forum.tvfool.com/attachment.php?attachmentid=3930&d=1603134589

http://forum.tvfool.com/attachment.php?attachmentid=3931&d=1603134652

Testing for spurs:

http://forum.tvfool.com/attachment.php?attachmentid=3932&d=1603135166

http://forum.tvfool.com/attachment.php?attachmentid=3933&d=1603135946

Then I decided to just wrap the plastic SDR enclosure in foil and turn On the Clock spur removal

http://forum.tvfool.com/attachment.php?attachmentid=3934&d=1603136471

CONCLUSIONS:

It is important to properly set the Reference level to display the correct SNR.

The RSP1A has a plastic enclosure that is letting strong signals through. I had hoped that the inside of the plastic enclosure had been sprayed with a conductive paint that would act like a shield, but apparently that wasn't done.

http://forum.tvfool.com/attachment.php?attachmentid=3937&d=1603204540

The aluminum foil that I put on the outside of the enclosure, and contacting the ground of the SMA antenna input connector, acted as a substitute shield.

http://forum.tvfool.com/attachment.php?attachmentid=3942&d=1603392963

The RSP2 looks like it has a conductive coating inside:

http://forum.tvfool.com/attachment.php?attachmentid=3938&d=1603213375

[rabbit73]

Have noticed that (spurs) in the low cost RTL devices. Most of the time not a problem if one is aware of their presence.

I found another scanner that can be used with the RTL-SDR.COM V3 dongle.
http://rfexplorer.com/touchstone/

The resolution isn't too good and there is no way to adjust the gain of the dongle. It is necessary to insert an attenuator before the dongle to obtain the correct representation of SNR.

But, the Touchstone software does cover more than one channel and you can see changes in real time. With the RTLSDR Scanner, you don't see the scan until it is completed.

http://forum.tvfool.com/attachment.php?attachmentid=3949&d=1603723275

http://forum.tvfool.com/attachment.php?attachmentid=3950&d=1603723331

The amount of attenuation must be found by trial-and-error. It helps if you have a TV that will tell you the SNR of a known signal.

The Toner attenuator shown above could be used.

http://forum.tvfool.com/attachment.php?attachmentid=3875&d=1600708146

My amateur Videos

I didn't use a preamp for this scan. The channel 16 signal (first strong signal on the left) measured -6.3 dBmV (-55.1 dBm) with my Sadelco DisplayMax 800 signal level meter:
https://www.dropbox.com/s/no068tnzs0jgtb2/%20%20%20%20Touchstone%20RF%20Spectrum%20Analyzer%202020-10-27%2014-45-43.mp4?dl=0

https://www.dropbox.com/s/no068tnzs0jgtb2/%20%20%20%20Touchstone%20RF%20Spectrum%20Analyzer%202020-10-27%2014-45-43.mp4?dl=1

When I used a 17 dB preamp (CM7777HD Amplify, low gain setting), more attenuation before the dongle was needed.
https://www.dropbox.com/s/18g3b36dmv8u26z/%20%20%20%20Touchstone%20RF%20Spectrum%20Analyzer%202020-10-27%2014-27-48.mp4?dl=0

https://www.dropbox.com/s/18g3b36dmv8u26z/%20%20%20%20Touchstone%20RF%20Spectrum%20Analyzer%202020-10-27%2014-27-48.mp4?dl=1

I use VLC Media Player.

If you want to be able to adjust the gain, you would need to purchase the Rational Waves RF SPECTRUM ANALYZER SOFTWARE:
http://rationalwaves.com/rationalwaves/

http://nutsaboutnets.com/supported-rf-analyzers/

But, I think it would be better to buy an SDRplay RSP1A and use the RSP Spectrum Analyser software.

When I used the 17 dB preamp with the SDRplay RSP1A and the RSP Spectrum Analyser software, I was able to adjust the Display Scale settings for a proper display:

http://forum.tvfool.com/attachment.php?attachmentid=3954&d=1604280723

The ADC is the Analog to Digital Converter in the SDR.

http://forum.tvfool.com/attachment.php?attachmentid=3956&d=1604282907

The channel 16 signal input to the RSP1A with the 17 dB preamp measured -35 dBm. I don't usually use the preamp; just wanted to see how the RSP Spectrum Analyser software would handle the stronger signal.

When the RSP1A is used with the SDRuno software, there is an overload warning if the gain is set too high. It did flash when the gain was set to MAX when using the 17 dB preamp. To avoid damage to the RSP1A, the input signal should be kept below 0 dBm (49 dBmV).

http://forum.tvfool.com/attachment.php?attachmentid=3957&d=1604284579

[tripelo]

Hi rabbit73, or anyone familiar with Airspy.

Do you know if there is software for the Airspy R2 that exports logs of spectrum scans in .csv format (or something similar)?

Interested in software for Airspy R2 that can log and export amplitude vs frequency, similar to RTLSDR Scanner.

The purpose would be to save signal data sets (many scans) for later comparison using Excel.

Thanks.

[eclipsme]

Are you familiar with rtl-sdr dot com? not sure I can post a url here -
https://www.rtl-sdr.com/big-list-rtl-sdr-supported-software/ has a large list of software.

I use with SDR# for tuning as well as Orbitron and WXtoimg to download satellite weather.

Also to check out signal strength from my TV antenna.

Rabbit started me on this journey. I am sure he will have other ideas for you.

[tripelo]

Are you familiar with rtl-sdr dot com? not sure I can post a url here -
https://www.rtl-sdr.com/big-list-rtl-sdr-supported-software/ has a large list of software.

Nice list of software, thanks.

RTLSDR Scanner is shown in the list. Used it several years ago with the least costly version of RTL-SDR dongle. RTLSDR Scanner with its export feature, worked fine for the specific application.

Looking for something similar that will work with Airspy R2.

Not sure how much, if any, of the software in that list, will work with the Airspy R2.

.

[eclipsme]

I have no direct experience running on Airspy , but as far as I know, it should. Why not give it a try and see what happens?

[rabbit73]

Do you know if there is software for the Airspy R2 that exports logs of spectrum scans in .csv format (or something similar)?

Interested in software for Airspy R2 that can log and export amplitude vs frequency, similar to RTLSDR Scanner.

Sorry, none that I know of.

[tripelo]

...Why not give it a try and see what happens?

Haven't tried it for a couple of reasons:

1. Do not yet possess Airspy R2.
2. Haven't seen on Internet where anyone has successfully used the combo.

The reason for Item #2 could be because the RTLSDR Scanner was designed to be used on the more common inexpensive RTLSDR devices. There appears to be considerable hardware differences between the lower cost devices and the Airspy.

Sorry, none that I know of.

Thanks, rabbit73.

.

[rabbit73]

1. Do not yet possess Airspy R2.
2. Haven't seen on Internet where anyone has successfully used the combo.

The only software that I know of that will produce CSV output is for the RF Explorer SA and the V1.1 RSP Spectrum Analyser for the SDRplay RSP1A:

http://forum.tvfool.com/attachment.php?attachmentid=3963&d=1606249794

http://forum.tvfool.com/attachment.php?attachmentid=3964&d=1606249811

[tripelo]

The only software that I know of that will produce CSV output is for the RF Explorer SA and the V1.1 RSP Spectrum Analyser for the SDRplay RSP1A:

Interesting, thanks for the info and images.

Seems the Airspy has such a good reputation, that there would be logging/export software available for it.

As we discussed earlier in this thread, interested in high dynamic range obtainable with either SDRplay RSP1 or Airspy R2.

Tend to favor the Airspy R2 over the RSP1 because it seems to display less spurs (indicating better dynamic range at least in spectral regions where spurs occur).

However, also would like to log and export data.

The specific high dynamic range application does not necessarily require logging, and the logging application does not necessarily require high dynamic range.

Therefore, an option could be to use Airspy R2 for high dynamic range tests and the low cost SDR dongle with RTLSDR Scanner software for logging.

.

[rabbit73]

Therefore, an option could be to use Airspy R2 for high dynamic range tests and the low cost SDR dongle with RTLSDR Scanner software for logging.

I wonder if the Bandscan approach would be suitable for any of your needs.
https://rabbitears.info/tvdx/all_tuners
Map takes a while to load.

https://m.rabbitears.info/index.php?request=tvdx_grid&tid=10311B6D&tno=0

https://rabbitears.info/tvdx/one_tuner_map/10311B6D/tuner0

http://forum.tvfool.com/attachment.php?attachmentid=3966&d=1606272557

[tripelo]

I wonder if the Bandscan approach would be suitable for any of your needs...

Yes, thanks for your thoughts on this topic, that approach could be quite helpful.

Having capability for logging signal quality over longer periods of time (at least 24 hours) would help in evaluating the performance hardware design changes.

Think most contributors to RabbitEars Bandscan use SiliconDust HDHomeRun tuners.

Recently purchased one of those tuners for the purpose of recording signal strength and signal quality.

According to Trip at RabbitEars, seems the software that produces the web display is not set up to export raw data to a file format that could be conveniently imported to Excel.

A person who developed a Windows version of that software said it would take some time, but he could add the option to make the export.

.

[rabbit73]

Having capability for logging signal quality over longer periods of time (at least 24 hours) would help in evaluating the performance hardware design changes.

Think most contributors to RabbitEars Bandscan use SiliconDust HDHomeRun tuners.
That is true. Here are Trip's instructions for setup:
Joining the Live Bandscan
https://www.rabbitears.info/static.php?name=join_live_bandscan

It is possible to modify the graph for clarity:

http://forum.tvfool.com/attachment.php?attachmentid=3967&d=1606317606

[tripelo]

...
It is possible to modify the graph for clarity:...

Yes, in many cases, the graphical images could be helpful.

Having the raw data to analyze, when looking for relatively small performance differences (say between two different antenna preamp combinations), could help to ascertain differences of less than one dB.

FYI:

Have designed, built, and tested several low-noise preamplifiers in combination with custom high gain antennas.

It is somewhat straightforward to evaluate relative noise figure of amplifiers, or the relative gain of antennas.

But more difficult to evaluate the performance of a particular preamplifier and antenna combination. The degree of impedance match or mismatch between amplifier and antenna can affect both noise figure and effective antenna gain.

Further complication is (in KY) receiving stations at 100 miles distant, there are large variations in signal levels vs time.

It is difficult to ascertain performance differences, especially when the performance difference may be a dB or even less.

.

[rabbit73]

Having the raw data to analyze, when looking for relatively small performance differences (say between two different antenna preamp combinations), could help to ascertain differences of less than one dB.
It would be necessary to compare then two systems at the same instant because OTA signals constantly vary in strength. I have seen OTA signals vary as much as 10 dB in 30 minutes.

I have more confidence in the results when using a constant strength transmitted test signal for a comparison.
But more difficult to evaluate the performance of a particular preamplifier and antenna combination. The degree of impedance match or mismatch between amplifier and antenna can affect both noise figure and effective antenna gain.
Very true. Keeping the preamp close to the antenna will minimize the mismatch loss. When you compare the two systems, that will tell you which has the superior performance.

Low noise preamps can make a difference on UHF if the ambient noise is below -100 dBm, but they don't seem to make much difference as compared to average NF preamps on VHF because of the higher ambient noise level on VHF, especially VHF-Low.

http://forum.tvfool.com/attachment.php?attachmentid=3879&d=1600731992

[tripelo]

It would be necessary to compare then two systems at the same instant because OTA signals constantly vary in strength...

That would be good if was practical. For accuracy, the two antennas would need to be located at the same physical place. In many cases at UHF, a separation of a foot or so, and the two antenna combos can receive different signals.

...I have seen OTA signals vary as much as 10 dB in 30 minutes.

Yes, at 100 mile path have seen variation of 10-15 dB in a minute or so.

...I have more confidence in the results when using a constant strength transmitted test signal for a comparison...

That can allow measurement of signal strength related to antenna gain.

But doesn't address realized noise figure, or realized signal quality.

...Keeping the preamp close to the antenna will minimize the mismatch loss...

In general, short transmission line minimizes transmission line losses.

Transmission line losses contribute directly to signal loss & degrade overall system noise figure.

However, even with virtually no transmission line, mismatch loss between antenna and preamp may still be present.

Mismatch has two main effects:

1. Signal loss which is is a result of reflection and reduces realizable antenna gain.
2. Degrades realizable noise figure of preamp.

The noise figure of the first active device in a preamp is dependent on the active device seeing a specified termination impedance.

Low noise preamps rarely have an input impedance of *real 75 Ohms*.

An antenna rarely has an impedance of real 75 ohms.

A preamp only has a specified noise figure when loaded with a specified complex impedance.
Preamps are usually tested for noise figure when terminated with 75 Ohms real impedance.

In reality, impedances of antennas are not real 75 Ohms and preamps input impedances are not real 75 Ohms.

So when combined;

- The realized antenna gain is less than optimum and
- The realized noise figure of the preamp is not as predicted.


-----------------
*real 75 Ohms*
-----------------

rabbit73, mainly for others benefit, realizing you know this:

Impedances generally are complex numbers, consisting of a real part and an imaginary part.

Usually denoted a R+jX or R-jX.

Where R=real and X=reactance, either inductive (+) or capacitive (-).

For perfect 75 Ohm match, the real part must be 75 Ohms and the reactance or imaginary part must be zero Ohms

.

[rabbit73]

That would be good if was practical. For accuracy, the two antennas would need to be located at the same physical place. In many cases at UHF, a separation of a foot or so, and the two antenna combos can receive different signals.
That is true because the wavefront is non-uniform. I have seen a difference in the scan of a channel when moving the antenna a foot horizontally.

http://forum.tvfool.com/attachment.php?attachmentid=3968&d=1606331232

But then, how is it possible for you to make a valid comparison of the performance of the two systems? Have the two antennas on a sliding carriage that moves each antenna into the same location, or what? Otherwise, how can you possibly get a comparison like you would on a lab grade antenna range? On a range, you would use a constant strength test signal and place each antenna, in turn, in the same location.

The closest I got to the ideal was to switch the two antenna locations, but I really wanted to be able to slide them sideways.

http://forum.tvfool.com/attachment.php?attachmentid=2160&d=1469629130

The white wall was just a background for the photo. The actual comparison was done at a location with OTA signals that were as constant as I could find. I used an A/B switch for a rapid comparison.

http://forum.tvfool.com/attachment.php?attachmentid=3970&d=1606334826

[eclipsme]

"But then, how is it possible to make a valid comparison of the performance of the two systems? Have the two antennas on a sliding carriage that moves each antenna into the same location? "

would splitting 1 feed to the 2 systems work? Then reverse the feeds to compensate for output differences of the splitter and average the results?

There *must* be something wrong with this idea (lol!) It is just too simple, and I am too ignorant!

But very interesting discussion!

[tripelo]

Rabbit73, looks like you have a good collection of equipment for portable testing.

Having a near field view over open water helps with signal reception.

]... how is it possible for you to make a valid comparison of the performance of the two systems?...

That depends on the accuracy one may be looking for and the test environment. If looking for accuracy in the one dB or less range, it may be very difficult.

... Have the two antennas on a sliding carriage that moves each antenna into the same location, or what? ...

That could be useful. Depending on the variability of the received signals and the length of time the test systems are evaluated.

... how can you possibly get a comparison like you would on a lab grade antenna range? ...

Probably not practical for most.

As you know, a lab grade antenna range is implemented in such a way to minimize all reflections that could be received in the main beam or sidelobes of the antenna under evaluation.

... On a range, you would use a constant strength test signal and place each antenna, in turn, in the same location...

Test ranges are usually setup to evaluate antennas loaded by a specified impedance. They do not usually evaluate antenna preamp combinations.

...The closest I got to the ideal was to switch the two antenna locations, but I really wanted to be able to slide them sideways...

If the signal variability is not too great, and the accuracy requirements are not too stringent, in most cases that probably works OK.


General comment:

All measurements have limits in accuracy. For most TV reception purposes, the measurements taken with less than optimum conditions may be satisfactory.

In comparative testing, if there variables that one cannot control. Some form of averaging to wash out the variability can be helpful.

In the case of systems receiving signals that vary with time, then time averaging can reduce the errors. If long enough time and enough samples are averaged for each system under test, then errors in measurement can be reduced.

===========================

...would splitting 1 feed to the 2 systems work? Then reverse the feeds to compensate for output differences of the splitter and average the results?...

If accuracy requirements are not too stringent, then what you seem to be suggesting can help with comparison of two preamps or two receiving systems.

However, the preamps may behave slightly different when connected to an actual receiving antenna with different transmission line and no splitter. In many case, this difference could be small enough to not matter to the individual performing the test.

.

[rabbit73]

Rabbit73, looks like you have a good collection of equipment for portable testing.
Thank you for your comments.

My wife supported my experiments, so I was able to collect the equipment I needed to solve reception problems.
Having a near field view over open water helps with signal reception.
Yes, the signals were quite constant, except when a boat went by in the signal path.:)
That depends on the accuracy one may be looking for and the test environment. If looking for accuracy in the one dB or less range, it may be very difficult.
Yeah, I never felt I needed an attenuator with 0.1 dB steps.
As you know, a lab grade antenna range is implemented in such a way to minimize all reflections that could be received in the main beam or sidelobes of the antenna under evaluation.
Yes, reflections are an ever present problem.

Kent Britain, WA5VJB, creator of the Cheap Yagi, would place the antennas at ground level to minimize ground reflections during antenna shootouts. I tried that with indoor antenna tests. The results were consistent with results at 3 ft above the floor, but the signals were about 20 dB weaker on the floor (concrete slab covered with carpet).
http://www.wa5vjb.com/references/Antenna%20Measuring%20Notes-keb.pdf

WA5VJB Antenna Measuring Notes, Extract

Kent Britain WA5VJB (Written for Scatterpoint issue 1-2000 updated Sept 2006)

Since 1987 I have set up my portable antenna range at 26 Conferences measuring well over 1500 antennas, mainly in the 0.9 to 24 GHz range. G4DDK has asked me to list some of my observations.

Open Area:

30 to 40 Meters is nice, but I have often set up in more confined areas of 10 to 20 Meters. But I try to avoid areas near walls that might cause reflections. Given a choice, I set up on grass (easier on my feet) but parking lots can also be used. The whole idea is to find an area where you have a consistent signal about the same size as the capture area of the antenna. i.e. a bit bigger than the biggest antenna you plan to test. Our greatest source of error is having the signal level on one edge of the dish stronger than on the other edge of the dish.

I gave up on elevated ranges a few years ago. I almost always set up with the source antenna (Usually a horn) sitting right on the ground. Thus the antenna and its reflected image are virtually the same point. Sometimes the horn is sitting on a sheet of metal, sometimes it's sitting on a sheet of absorber. Sheets of the Carbon loaded foam work well if you don't have an Eccosorb. Also the sheet of magnetic material that hold advertising to your fridge work well as Iron loaded absorber. The sheet metal gives me a little more signal; the absorber usually gives me a cleaner test area. Although there is no hard fast rule here, I just use what ever works best. If there is a nice consistent signal area, we start measuring antennas!
END OF EXTRACT

http://forum.tvfool.com/attachment.php?attachmentid=2661&d=1495302313

http://forum.tvfool.com/attachment.php?attachmentid=2662&d=1495302363

If the signal variability is not too great, and the accuracy requirements are not too stringent, in most cases that probably works OK.
My conclusion, also.
In comparative testing, if there variables that one cannot control. Some form of averaging to wash out the variability can be helpful.

In the case of systems receiving signals that vary with time, then time averaging can reduce the errors. If long enough time and enough samples are averaged for each system under test, then errors in measurement can be reduced.
That sounds like the best approach for your comparisons, since you are not just comparing antenna and preamp combinations, but antenna, preamp, and antenna location combinations.

_____________________________

Happy Thanksgiving!

Hope you are staying safe.

Best regards,
rabbit73

[tripelo]

..My wife supported my experiments, so I was able to collect the equipment I needed to solve reception problems.

Very good to have cooperation from spouse.

Thanks for the .pdf, interesting read.

Wonder how you use the BT double sideband Modulator?

Do you inject a tone to provide a pair of CW signals, or add a DTV baseband. or something else?

...Happy Thanksgiving!

Hope you are staying safe...

Thanks, happy holidays to you.

.

[rabbit73]

Wonder how you use the BT double sideband Modulator?

Do you inject a tone to provide a pair of CW signals, or add a DTV baseband. or something else?

http://forum.tvfool.com/attachment.php?attachmentid=3972&d=1606501894

My use is very simple. I don't have a UHF signal generator, so I use the NTSC video carrier of the modulator as a constant strength test signal. All I have to do is select an output channel on the Agile Modulator and tune my signal level meter or SDR to that frequency. It isn't necessary to modulate the carrier, the video carrier exists without video or audio input.

http://forum.tvfool.com/attachment.php?attachmentid=3971&d=1606500200

For VHF, I use a more sophisticated (and expensive) source; I generate an ATSC 1.0 carrier with my Thor Petit Modulator.

http://forum.tvfool.com/attachment.php?attachmentid=3973&d=1606503206

http://forum.tvfool.com/attachment.php?attachmentid=3978&d=1606517223

http://forum.tvfool.com/attachment.php?attachmentid=3979&d=1606518082

Testing the Thor Petit HDMI RF MODULATOR
https://www.avsforum.com/threads/testing-the-thor-petit-hdmi-rf-modulator.3095882/

[tripelo]

...
My use is very simple. I don't have a UHF signal generator, so I use the NTSC video carrier ...exists without video or audio input.

OK, yes.

Not that it would be a serious problem for most antenna testing;

Being a double sideband modulator, doesn't the NTSC video carrier show up twice in the spectrum?

For VHF, ... generate an ATSC 1.0 carrier with my Thor Petit Modulator.

Doesn't the Thor Petit also cover UHF?

.

[rabbit73]

Being a double sideband modulator, doesn't the NTSC video carrier show up twice in the spectrum?
Yes, it does; that is why you can only use every other channel when adding a channel. But, all I have to do is tune my SLM or SDR to the video carrier frequency of the channel transmitted by the modulator.

http://forum.tvfool.com/attachment.php?attachmentid=2848&stc=1&d=1502665287

http://forum.tvfool.com/attachment.php?attachmentid=3974&d=1606507557

Doesn't the Thor Petit also cover UHF?Yes, it does, but I didn't have it at first because it was so expensive. I waited until it went on sale, which it is also now again.

The video carrier is more precise; the ATSC signal is much wider and not always flat. So, where do you measure the ATSC Carrier when it isn't flat? My SLM takes an average of many readings when it scans the whole ATSC channel, but can measure the NTSC video carrier more exactly. With the SDR, I can select the measurement frequency at any place on the ATSC channel.

http://forum.tvfool.com/attachment.php?attachmentid=3975&d=1606508676

http://forum.tvfool.com/attachment.php?attachmentid=3976&d=1606508775

http://forum.tvfool.com/attachment.php?attachmentid=3977&d=1606516308

[tripelo]

Thanks for the images.

Looks like displays from three different STL-SDR units,
that is if the RTLSDR Scanner is running on one of the lower cost devices?

When comparing the SDRplay and the Airspy,
noticed the noise spectrum on the lower frequency side of Channel 3 is different for each.

Specifically, the noise is increasing near lower edge of Ch3 for the SDRplay,
for the Airspy decreases a bit near lower edge of Ch 3.

Wonder if that reoccurs, repeatable?

.

[rabbit73]

Looks like displays from three different STL-SDR units,
that is if the RTLSDR Scanner is running on one of the lower cost devices?

That is correct. The last three images were:
1. RTL-SDR.COM V3 dongle with free open-source Scanner software from GitHub
2. SDRplay RSP1A SDR with SDRuno software
3. Airspy R2 SDR with Spectrum Spy software that is included with the SDR# (SDRsharp) software download
When comparing the SDRplay and the Airspy,
noticed the noise spectrum on the lower frequency side of Channel 3 is different for each.

Specifically, the noise is increasing near lower edge of Ch3 for the SDRplay,
for the Airspy decreases a bit near lower edge of Ch 3.

Yes; three factors account for that:
1. The noise floor is not constant on VHF, especially VHF-Low; the scans were done at different times
2. The RSP1A with the SDRuno software is limited to a useful bandwidth of about 8 MHz; each side falls off pretty fast. The Airspy R2 with the Spectrum Spy software has an extremely wide bandwidth for a scan only limited to the full bandwidth of the R2.
3. The bandwidth of the antenna

http://forum.tvfool.com/attachment.php?attachmentid=3980&d=1606523160

[tripelo]

...The RSP1A with the SDRuno software is limited to a useful bandwidth of about 8 MHz; each side falls off pretty fast.

OK, understood.

..The Airspy R2 with the Spectrum Spy software has an extremely wide bandwidth for a scan only limited to the full bandwidth of the R2...

OK, not understood :)

Can the Airspy not scan & display a narrow 8-10 MHz region like the RSP1?

When the RSP1 scans from say 45 MHz to 80 MHz,
does the spectrum look like the Airspy R2 spectrum at the lower part of Channe 3?

.

[rabbit73]

Can the Airspy not scan & display a narrow 8-10 MHz region like the RSP1?
The Airspy R2 can scan 8 MHz with the SDR# software, similar to what the RSP1A does with the SDRuno software. It is important to set the gain at the correct level to obtain the proper presentation of the SNR; too much or too little will show the wrong SNR. Increase gain until the adjacent noise floor just starts to rise and the signal no longer increases in strength. That point should show MAX SNR.

http://forum.tvfool.com/attachment.php?attachmentid=3981&d=1606528894

R2 and Spectrum Spy at 10 MHz width:

http://forum.tvfool.com/attachment.php?attachmentid=3982&d=1606533033

When the RSP1 scans from say 45 MHz to 80 MHz,
does the spectrum look like the Airspy R2 spectrum at the lower part of Channe 3?
As I said earlier, the RSP1A can only scan 8-10 MHz with the SDRuno software. It can only do a wider scan using the RSP Spectrum Analyser software (the software that you said has too many spurs). Some of the "spurs" are actually pilot carriers of weak ATSC signals. Some are noise spikes. Some are clock spurs that can be removed before a scan.

50 MHz width with RSP1A and RSP Spectrum Analyser:

http://forum.tvfool.com/attachment.php?attachmentid=3984&d=1606535050

I don't actually have an RF channel 3 in this area, or any 2-6 channel. That is why I bought the Thor modulator to simulate an RF 3 ATSC channel. I have been studying the affect that a high noise level has on the reception of VHF-Low channels.

I first became interested in that project while trying to help a Canadian receive RF 2 and 4. I thought a CH3 folded dipole had a chance of receiving both. He was having no luck using an FM folded dipole of twinlead with 30 gauge conductors. I encouraged him to make a CH3 FD with larger diameter conductors, but he seemed unwilling to do it. I suspected that he had sufficient signal strength, but a high noise level. He was able to receive 9 OK.

http://forum.tvfool.com/attachment.php?attachmentid=3988&d=1606575802

http://forum.tvfool.com/attachment.php?attachmentid=3985&d=1606574455

http://forum.tvfool.com/attachment.php?attachmentid=3987&d=1606574746

I have two CH3 folded dipoles. I have one connected to the output of the Thor modulator. The other is connected to my SDR or a TV. It picks up the CH3 ATSC signal from the Thor modulator as if it were an OTA signal AND the ambient noise. This tells me how much stronger a VHF-Low signal needs to be for a sufficient SNR above the ambient noise.

If you want a specific test done, I could set it up over the weekend. I don't keep the CH3 folded dipoles set up in my room. I would need to know exactly what test you want me to do.

I could try to do 45 to 80 with all three SDRs, but it would require both CH3 folded dipoles to pick up the ambient noise.

[tripelo]

...RSP Spectrum Analyser software (the software that you said has too many spurs). Some of the "spurs" are actually pilot carriers of weak ATSC signals. Some are noise spikes. Some are clock spurs that can be removed before a scan...

Yes, OK.

..I have two CH3 folded dipoles. ...This tells me how much stronger a VHF-Low signal needs to be for a sufficient SNR above the ambient noise....

Understood.

...If you want a specific test done...

Thanks.

Appreciate the offer, but not necessary.

Your several images in this thread provide a fairly good idea of what can be expected from the RTL-SDR devices.

-----------------------

One of the specific tests planned in KY:

To determine if the 3rd order IMD from a broadcast station can be seen on one of these devices. The station IMD3 is strongest very near the edges 6 MHz spread. However, those edges are also where the SDR-RTL internal IMD may be highest. Therefore, it may be difficult to see low level station IMD with such devices.

Another requirement for such an observation is for the broadcast station to be fairly well isolated from any other stations and have a high S/N ratio (in some case 50 dB or more). This condition may not be met in populated areas (cities, etc). There is a PBS station in rural KY that meets such criteria.

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Appreciate the patience, tests, and and images you have displayed in this thread and others.

.