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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/xdysaeqzc3...27-59.mp4?dl=0 https://www.dropbox.com/s/xdysaeqzc3...27-59.mp4?dl=1 hide controls https://www.dropbox.com/s/nl1876xejj...32-41.mp4?dl=0 https://www.dropbox.com/s/nl1876xejj...32-41.mp4?dl=1 Spectrum Spy for R2 still https://i.imgur.com/xHTWPh5.jpg https://www.dropbox.com/s/gars272dis...12-56.mp4?dl=0 https://www.dropbox.com/s/gars272dis...12-56.mp4?dl=1 |
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73 post by majortom about 1/4 wave stubs use 7th harmonic https://www.digitalhome.ca/threads/o...5/post-3109007 |
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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/q79o3x433h...41-08.mp4?dl=0 https://www.dropbox.com/s/q79o3x433h...41-08.mp4?dl=1 |
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https://i.imgur.com/UfT7GDN.jpg https://i.imgur.com/iTqlYVK.jpg Quote:
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/9...c/Radar-FM.png Makes me wonder about FM interference. |
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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 |
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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. Quote:
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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.../post-59870798 Quote:
I think the calibration feature of the SDRuno mentioned above is fixed in the hardware or firmware. Quote:
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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. |
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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. ------------------- Quote:
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Using an Attenuator to Measure the Strength of a Digital TV Signal
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/searchma...145947&opkey=C https://i.imgur.com/jua41AY.jpg This was my setup: Code:
I added attenuation, for a total of 30 dB, to bring the signal down to 15 dB SNR at the "Digital Cliff." Code:
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. |
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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 |
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That is quite a difference between your calibrated RSP1a and the Airspy. . |
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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/exa...art-1.2005866/ |
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...-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: Quote:
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 |
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My account has finally been activated. I PM'd the "admin" user and was approved last night I guess. Cue this clip! :)
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A little late, but they finally got to you. Quote:
Welcome, verder; you are now "somebody" on the TVFool website. |
Welcome. I have been following along, picking up a few things along the way.
Congrats! |
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