HFU HF Underground
Technical Topics => SDR - Software Defined Radio => Topic started by: ChrisSmolinski on August 20, 2019, 1748 UTC
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Which SDR is best for DGPS decoding? For my nightly recording sessions I use my AFE822x, it has always provided higher decode rates than my netSDR. But wait, isn't the netSDR a "better" receiver since it has a 16 bit A/D? Well yes and no. Or maybe "it depends".
The DGPS band is 285-325 kHz, so these results may be applicable to NDB enthusiasts as well.
In the case of DGPS decoding in particular, you want to maximize the dynamic range, use as many of those A/D bits as possible. The AFE822x has a programmable gain amplifier on the front end. I can crank up the gain to maximum, because I feed my antenna through a LW low pass filter which kills the MW and SW bands, and prevents overloading. I always get better results (more decodes) with the AFE822x vs the netSDR. For general purpose listening, I don't notice much of a difference. The netSDR may be slightly better, or it could be my imagination. But there is no real objective way to tell which one "sounds better".
For a fair comparison, I fed the antenna through the LW low pass filter and then a splitter to each receiver, and recorded the DGPS band over the same time period. Since I had three receivers to test but only a two port splitter, this necessitated running two sets of tests.
For the antenna I used my 950 ft LoG (Loop on Ground) antenna, which is fed via one of my Cyclops antenna transformers and then coax to the shack
https://www.blackcatsystems.com/rf-products/cyclops_rf_ham_shortwave_radio_matching_transformer.html
These tests were done in the late morning and early afternoon. Not prime longwave/DGPS reception time, but it was convenient. Normally I use my 500 ft northeast terminated beverage/longwire, but I did some quick tests with the LoG this morning and it seemed to be producing stronger signals. That is something else to check, is this only the case daytime, or also at night?
All decoding done with Amalgamated DGPS of course, the premier DGPS decoding software. https://www.blackcatsystems.com/software/dgps_decoding_software_sdr.html
AirSpyHF+ Discovery vs AFE822x
AirSpyHF+ Discovery:
Count ID ref1 ref2 kHz Baud City Country Lat Lon km Deg
20 799 044 045 290.0 200 Penobscot, ME United States 44.453 -68.776 858 49
882 778 192 193 292.0 100 Kensington, SC United States 33.491 -79.349 723 198
348 929 312 313 296.0 200 St Jean Richelieu, QC Canada 45.324 -73.317 693 24
57 838 116 117 319.0 200 Detroit, MI United States 42.306 -83.103 590 301
2780 772 198 199 306.0 200 Acushnet, MA United States 41.749 -70.889 561 64
2684 844 094 095 324.0 200 Hudson Falls, NY United States 43.272 -73.542 489 35
1034 839 118 119 322.0 100 Youngstown, NY United States 43.239 -78.972 427 338
2099 803 006 007 293.0 100 Moriches, NY United States 40.794 -72.756 378 70
1856 806 012 013 289.0 100 Driver, VA United States 36.963 -76.562 307 173
3219 804 008 009 286.0 200 Sandy Hook, NJ United States 40.475 -74.02 266 70
AFE822x:
Count ID ref1 ref2 kHz Baud City Country Lat Lon km Deg
396 778 192 193 292.0 100 Kensington, SC United States 33.491 -79.349 723 198
88 929 312 313 296.0 200 St Jean Richelieu, QC Canada 45.324 -73.317 693 24
2711 772 198 199 306.0 200 Acushnet, MA United States 41.749 -70.889 561 64
2520 844 094 095 324.0 200 Hudson Falls, NY United States 43.272 -73.542 489 35
998 839 118 119 322.0 100 Youngstown, NY United States 43.239 -78.972 427 338
1998 803 006 007 293.0 100 Moriches, NY United States 40.794 -72.756 378 70
1745 806 012 013 289.0 100 Driver, VA United States 36.963 -76.562 307 173
3051 804 008 009 286.0 200 Sandy Hook, NJ United States 40.475 -74.02 266 70
The Discovery wins, with more decodes from each station, as well as picking up several weaker stations completely missed by the AFE822x.
AirSpyHF+ Discovery vs netSDR
AirSpyHF+ Discovery:
68 799 044 045 290.0 200 Penobscot, ME United States 44.453 -68.776 858 49
606 778 192 193 292.0 100 Kensington, SC United States 33.491 -79.349 723 198
52 929 312 313 296.0 200 St Jean Richelieu, QC Canada 45.324 -73.317 693 24
34 838 116 117 319.0 200 Detroit, MI United States 42.306 -83.103 590 301
1895 772 198 199 306.0 200 Acushnet, MA United States 41.749 -70.889 561 64
1912 844 094 095 324.0 200 Hudson Falls, NY United States 43.272 -73.542 489 35
624 839 118 119 322.0 100 Youngstown, NY United States 43.239 -78.972 427 338
2011 803 006 007 293.0 100 Moriches, NY United States 40.794 -72.756 378 70
1954 806 012 013 289.0 100 Driver, VA United States 36.963 -76.562 307 173
3040 804 008 009 286.0 200 Sandy Hook, NJ United States 40.475 -74.02 266 70
netSDR:
Count ID ref1 ref2 kHz Baud City Country Lat Lon km Deg
1695 803 006 007 293.0 100 Moriches, NY United States 40.794 -72.756 370 75
1533 806 012 013 289.0 100 Driver, VA United States 36.963 -76.562 340 173
2508 804 008 009 286.0 200 Sandy Hook, NJ United States 40.475 -74.02 258 77
A clear winner here, the netSDR is pathetic on the DGPS band.
The next step is to run the Discovery overnight, recording DGPS. Perhaps sharing the same antenna as the AFE822x, and then another night with different antennas to each receiver.
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Since you used a splitter, was there any isolation between the two SDRs?
Definitely do night tests with the splitter. One when things are quiet (i.e. no stupid t-storms) and even another when the stupid t-storms are around. See how they both react to that interference.
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Since you used a splitter, was there any isolation between the two SDRs?
They shared a common ground. I'll do some more tests today with other SDRs. I am tempted to throw together a 4 port splitter so I can test a bunch of them at once. Could be useful for HF and MW comparisons also. I am a big fan of testing radios against each other with the same antenna at the same time. The tests you usually see where someone switches back and forth between radio A and B are problematic, as propagation can change in just a few seconds.
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I just got my Airspy Discovery this week; started playing around with it and comparing it to my Afedri. I run 2 copies of SDR-Console, and the radios are on the same 40m dipole through a stidsberg multicoupler. The one difference is the Afedri is using 50 ohm coax and the Discovery 75 ohm (RG-6 quad shield because that's what I had sitting here).
So far, they seem to pull in the same signals. The main non-scientific subjective difference I've noticed is that the Discovery has a better SNR. It's a lot quieter. One thing to note is that I live in a fairly rural area with low noise and no strong signals that overload things. So I'm the wrong person to ask if anyone is interested in how the radios compare in overloaded situations.
I'll do some more comparisons and post results; I'll post a youtube video with the consoles running side-by-side if I can figure out how to record my screen.
Bottom line - I'm definitely impressed with the Discovery and have no regrets getting it. It's performing well and actually comes out a bit cheaper than the Afedri.
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Was gonna ask about the snr for each rig. If they're not the same, that will effect the outcome as far as comparing apples to apples.
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Was gonna ask about the snr for each rig. If they're not the same, that will effect the outcome as far as comparing apples to apples.
Yeah, I'm trying to figure out the right baseline. The gain options are very different for each, at least how SDR Console implements them. And the response when one switches gain is different as well. I'm going to try to do a video this weekend. I'll show the different gain options and what they do, and those who have more experience can help figure it out.