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OTA recommendations
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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?opt...pper&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 |
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We will study your problem and come back with some comments that might be helpful. |
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Here is a signal report for your location:
https://www.rabbitears.info/searchma...tudy_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_wr...9038e93d573093 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. |
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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 Quote:
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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. |
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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. |
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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/20170627...r-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/c...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 |
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Thanks! Was it worth it? Nice cheap alternative for someone that barely understands what this is! |
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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/ge923irqji...50-56.mp4?dl=0 https://www.dropbox.com/s/ge923irqji...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 |
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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. |
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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. Quote:
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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/8gsw9t1zsr...Path2.mp4?dl=0 https://www.dropbox.com/s/8gsw9t1zsr...Path2.mp4?dl=1 this is what the signal looks like with a strong wind: https://www.dropbox.com/s/ig3va499k2...Path4.mp4?dl=0 https://www.dropbox.com/s/ig3va499k2...Path4.mp4?dl=1 |
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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... |
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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. |
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I will not post any images without your permission. |
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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 Quote:
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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?...s&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/eusj9k25wg...08-07.mp4?dl=0 https://www.dropbox.com/s/eusj9k25wg...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/fnjyuttou2...54-35.mp4?dl=0 https://www.dropbox.com/s/fnjyuttou2...54-35.mp4?dl=1 |
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I will try to find some antenna patterns; they are getting hard to find. |
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https://i.imgur.com/FFvapU1.jpg http://www.m4antenna.eastmasonvillew...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. |
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/maycre...setup/mclapp-4 https://www.youtube.com/watch?v=4dNP4vuQ9Z0 Outstanding work as usual, rabbit73! All the best..... |
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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 Quote:
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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. |
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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 |
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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/hzmz4mvte4...50-57.mp4?dl=0 https://www.dropbox.com/s/hzmz4mvte4...50-57.mp4?dl=1 CH 16 https://www.dropbox.com/s/0jlgno1gtj...02-31.mp4?dl=0 https://www.dropbox.com/s/0jlgno1gtj...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/tutoria...h-snr-ber-mer/ |
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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. Quote:
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Use those tools to improve signal strength and signal quality. |
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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. Quote:
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/searchma...tudy_id=145947 Quote:
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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. |
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https://i.imgur.com/BBrbazI.jpg https://i.imgur.com/UO1EckC.jpg https://i.imgur.com/AzQcUvN.jpg Quote:
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/mj126w9mt2...37-37.mp4?dl=0 https://www.dropbox.com/s/mj126w9mt2...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/comm...o_idea_whyany/ click on VIEW ENTIRE DISCUSSION for this: Quote:
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https://www.rabbitears.info/searchma...tudy_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 |
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To give you a feeling for signal levels, here is your report in dBm: https://www.rabbitears.info/searchma...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/h...4/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. |
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. |
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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: Quote:
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/ig3va499k2...Path4.mp4?dl=0 https://www.dropbox.com/s/ig3va499k2...Path4.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. |
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I should have shown the math to support my statement. Quote:
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_c...ask=view&id=57 Quote:
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 Quote:
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. Quote:
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. |
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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: Code:
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-att...ant=1083705673 https://www.newark.com/webapp/wcs/st...4899&mf=106654 |
Measuring Signal Margin to Dropout
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 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. |
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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 |
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