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Old 1-Oct-2015, 5:15 PM   #1
DStank
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Join Date: May 2015
Posts: 6
Under 10 miles but still having trouble

Hello, I am having decent reception but would like to improve it if possible. My setup is a HD Frequency Cable Cutter antenna, currently connected straight into a TiVo Roamio OTA DVR with a 12ft RG6 cable.

I have a spare cable amplifier from a previous Comcast installation that I haven't tried using yet. I've moved the TiVo & Antenna to the second floor. I would prefer it on the first floor but the reception seems better upstairs.

I would like to place the antenna in the attic but I'm unsure how a long cable run might affect the signal. My house is two-story plus attic and a basement. If the antenna ends up in the attic the cable will run from the attic into the basement then back up to the first floor to the TiVo. So maybe about 60 feet of RG6 and a few barrel connectors.

For the nearby channels I'm trying to receive the TiVo reports the signal strength from 60-75 (0-100 scale). Generally that seems to be okay but every couple of minutes, some channels more than others, I have pixelation.

Being as close as I am to the stations broadcast I was hoping to be able to get over 90 on TiVo's signal strength and have no issues.

Here's my TV Fool Signal Analysis Results:
http://www.tvfool.com/?option=com_wr...8e03b98b2c9c0f

What can I do get the best results?
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Old 1-Oct-2015, 8:43 PM   #2
MikeBear
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First of all, a Tivo Roamio being used for OTA tv is incapable of showing a signal level higher than 72 maximum. If you watch the signal screen as it calibrates to the channel being received, it'll go down then UP, and then settle to it's final value.

It's true they can show a higher signal level when used with a cable tv connection, just NOT for OTA tv for whatever reason. This has been hashed out over at the Tivo Community forums.

So, be very happy with a signal level of 72, as that's the best! 40 is the lowest before you'll have serious issues. You need to concern yourself with signal QUALITY though. So your pixelation problem is another issue, and I'll leave that to being answered by Rabbit and others. They'll either get you going, or you'll KNOW you'll have to settle for what you have.

You should also run an "FMFOOL" report, and post a screen print of that here. http://fmfool.com/
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Old 1-Oct-2015, 8:56 PM   #3
rabbit73
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Thanks for adding your experience with the TiVo, Mike.

While I was reading his post I did an FMFOOL report (see attachment) for his estimated location, in Redford Charter Twp, near Livonia MI, because they don't link like TVFOOL reports. He can do his own to see how they compare.

Your hunch was accurate because he has a very strong FM signal that might interfere with TV reception, and might need an FM filter.
http://www.mcmelectronics.com/produc...-FM-88-/33-341
a HLSJ (use high and common ports) also makes a good filter that attenuates everything below Channel 7 including the FM band with low loss for the TV signals:
http://www.solidsignal.com/pview.asp?p=zhlsj

Hello, DStank:
You also have some very strong TV signals which might cause overload, but it might be multipath reflections because of the indoor location causing poor signal quality. Monitor the SNR and uncorrected errors on the TiVo to find the best antenna location.

If your TV has a digital tuner, you can compare the reception of the TiVo with the reception of the TV.
Quote:
I have a spare cable amplifier from a previous Comcast installation that I haven't tried using yet.
Unless your indoor losses are more than average, you shouldn't need (or use) that amp because of your very strong signals. What model is the amp?

WKBD is your strongest signal with a Noise Margin of 69.7 dB even before adding the antenna gain.



Interpreting Noise Margin in the TV Fool Report

http://www.aa6g.org/DTV/Reception/tvfool_nm.html

Quote:
I would like to place the antenna in the attic but I'm unsure how a long cable run might affect the signal.
Attic losses are difficult to predict. A metal roof, aluminum foil thermal barrier, aluminum siding, and stucco can block signals, as can trees and other buildings.
Quote:
I'm unsure how a long cable run might affect the signal.
The loss for RG6 is about 6 dB per 100 ft at UHF; you have plenty of dB to spare.
Quote:
maybe about 60 feet of RG6 and a few barrel connectors.
Sometimes F81 barrel connectors can cause a problem with a poor connection. I check mine by inserting a short length of 18 gauge bare solid copper wire (same size as the center conductor of RG6 coax) to see if the F81 grabs it firmly.

Try your HD Frequency Cable Cutter antenna in the attic with a temporary setup to see how it does before drilling any holes. Then add some more cable to simulate a basement run.
Quote:
Generally that seems to be okay but every couple of minutes, some channels more than others, I have pixelation.
What channels are giving you a problem? Which channels are OK?

You might need to settle for one direction, like 50 degrees magnetic, for a good selection of desirable channels, instead of expecting to get all channels from all directions, which is unrealistic.

If your HD Frequency Cable Cutter antenna doesn't do what you want in the attic, consider using an Antennas Direct C2V up there. It has a reflector that makes the antenna directional to reject troublesome signal reflections, but has a 70 degree beamwidth to receive the grouping of signals coming from the NE.
https://www.antennasdirect.com/clear...ntalplane.html
https://www.antennasdirect.com/store...-Complete.html
http://www.bestbuy.com/site/antennas...=1218809260470
Attached Images
File Type: jpg DStankTVF FM est.JPG (104.5 KB, 509 views)
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Last edited by rabbit73; 4-Oct-2015 at 7:37 PM.
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Old 2-Oct-2015, 3:50 PM   #4
DStank
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Thanks for the great replies. MikeBear, you're absolutely right about 72 being the highest signal. I watched it longer to confirm and it does tend to peak and settle at 72. Previously I ballparked the 60-75 figure after observing the signal levels fluctuate.

WADL seems to be the one with consistently lower levels, fluctuating around 50. I am seeing some pixelation on that station. The other problem stations are WDIV, WTVS, & WXYZ. Even at 72 signal I see the pixelation. Sometimes it goes for a few minutes without any but usually more often though brief.

Rabbit's location on the FMFOOL is accurate, mine came out the same. In the TiVo diagnostics I am seeing uncorrected errors for my problem stations. It also shows 23-29db SNR. Seemed pretty steady at 29 for most. But it sounds like I should try one or both of those filters. I don't suppose there's any local stores that sell those.

I think before I do that I'll play around with my antenna location more. I'll get a longer cable and try putting it up into the attic and also outside to see if I can get a spot with less reflection issues. I have vinyl siding and asphalt roof. I don't think there is any aluminum; just drywall, insulation, and wood.

Rabbit, you mention the Antennas Direct C2V. I wonder if I would have better luck with that antenna. When I purchased HD Frequency Cable Cutter I came down to basically deciding between those two. The Wirecutter review pushed my choice to the HD Frequency Cable Cutter.

I'll find the cable amp tonight and post what model it is. It sounds like it shouldn't be used though. My understanding was it was needed to feed cable TV to an 8 line split in my previous previous house. This setup with the TiVo doesn't require me to use any splitters. However the TiVo does have 4 tuners so the signal must be split amongst them somehow.
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Old 3-Oct-2015, 1:16 AM   #5
rabbit73
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Quote:
The other problem stations are WDIV, WTVS, & WXYZ. Even at 72 signal I see the pixelation.
That sounds like overload from strong TV or FM signals to me. Try inserting an attenuator in the coax. A splitter can be used as an attenuator; 3.5 dB for a 2-way, 7 dB for a 4-way.
https://www.antennasdirect.com/store...ttenuator.html
http://www.3starinc.com/drop_in-line_attenuator.html
http://home-automation.smarthome.com...=&w=attenuator
http://mjsales.net/collections/atten...ant=1083705673
•Attenuation values 1, 3, 6, 8, 10, 12, 16, 20dB (FAM)
click on 1 dB for other values; the up and down arrows are faint

Quote:
Rabbit, you mention the Antennas Direct C2V. I wonder if I would have better luck with that antenna.
Try your present antenna with attenuators and FM trap or HLSJ first, then decide.
Quote:
However the TiVo does have 4 tuners so the signal must be split amongst them somehow.
It probably has an internal amp to compensate for the split.
__________________
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Last edited by rabbit73; 3-Oct-2015 at 1:37 AM.
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Old 3-Oct-2015, 9:10 PM   #6
DStank
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Quote:
Originally Posted by rabbit73 View Post
What model is the amp?
Viewsonics VSMA-601C

I haven't had much time to play around with the antenna's positioning yet. Hope to this weekend though.

Quote:
Originally Posted by rabbit73 View Post
Try inserting an attenuator in the coax. A splitter can be used as an attenuator; 3.5 dB for a 2-way, 7 dB for a 4-way.
Won't adding the splitters for attenuation kill my weak stations though?
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Old 3-Oct-2015, 10:42 PM   #7
rabbit73
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Thanks for the information on the Viewsonics VSMA-601C.

Quote:
Won't adding the splitters for attenuation kill my weak stations though?
On the contrary, it might save a weak station, like WADL.

There is such a thing as a signal that is too strong; more is not always better.

If your signals are too strong, they can overload an amp or tuner. When an amp or tuner is overloaded, it creates spurious signals within the device itself from IMD (Intermodulation Distortion) that can damage your weakest signals.

It does seem counterintuitive to amplify a signal and then attenuate it, and it took me a long time to understand why it might help.

Yes, when you insert an attenuator of 1 dB, it will make All signals 1 dB weaker. But if you have IMD products being created from overload, they will be reduced 3 dB for every 1 dB of attenuation, giving you a net gain of 2 dB. So, if you insert 3 dB attenuator, it can improve the SNR of your weak signal by 6 dB.

I have done many overload tests; here are some of my results:



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.

Intermodulation Distortion

The IMD creates new spurious signals within the preamp (or tuner) itself that can interfere with the reception of your weakest desired signals if the spurious signals are stronger than the noise floor of the weakest desired signals. The spurious signals are caused by the interaction between two or more of your strongest signals.

IMD is not the only distortion that can be created within the preamp; you can also have distortion caused by signals so strong that the top of the strong signals are clipped, which causes compression of the signals. This can be seen if you increase the input to the preamp by, for example, 10 dB and the output increases by less than 10 dB.

Spurious Free Dynamic Range

The Spurious Free Dynamic Range needed is the difference in strength between your strongest signal and your weakest desired signal, plus 16 dB for the SNR of the weakest signal, using the dBm Pwr scale on your tvfool report. This difference is expressed in terms of dB, not dBm, because the original units are the same. The difference between the strongest signal and the weakest signal is the Signal Dynamic Range/Dynamic Range, which is 16 db less than the SFDR, because it doesn't include the SNR of the weakest signal.



Another way to think of SFDR is from the top of the strongest signal down to the bottom (noise floor) of the weakest desired signal. The top of the spurious signals must be at or below the noise floor of the weak signals if they are not to cause interference. The Signal Dynamic Range is from the top of the strongest signal down to the top of the weakest desired signal.
Attached Images
File Type: jpg ATTforOverload2_1_zps9754a33a (2).jpg (238.2 KB, 1858 views)
__________________
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Last edited by rabbit73; 3-Oct-2015 at 11:07 PM.
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Old 12-Oct-2015, 3:34 PM   #8
DStank
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Wanted to update on my results.

I found that positioning the antenna in the attic seemed to cure my breakups. Now I have run a cable from the antenna in the attic to the living room and after a few days of observing I am having zero problems with all my major local stations, even WADL! I can't quite get enough reception to get the broadcasts from Windsor (CBET) though.

Maybe sometime in the future I will try changing the setup with a splitter or filter but for now I'm quite pleased with my setup and reception. Rabbit thank you for the wealth of information. Seeing that it's working without compensating for overload it seems to be that multipath reflections were likely the primary problem and a cleaner elevated path was needed.
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Old 13-Oct-2015, 12:16 AM   #9
rabbit73
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Thanks for your report of improved reception; glad to hear that our advice helped you.
__________________
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http://www.megalithia.com/elect/aeri...ttpoorman.html
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