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Sample rate / filtering interaction on the xA4
Posted: Wed Sep 20, 2023 4:37 pm
by shc
Is there any documentation on how filtering configuration is handled on the xA4? I am using SDRangel as a test bed and am seeing behavior I do not understand. The receiver configuration is shown in the linked images. The input signal is at -60 dBm in all cases.
Sample rate 2083335 Hz and above:
- The spectrum for a 1000.2 MHz signal looks like this. The signal strength is about right, but the noise floor looks strange.
- At 1001.1 GHz we get this. The signal is aliased to ~999.02 MHz and is down by only ~15 dB.
Sample rate 2083334 Hz and below (1 Hz less than the case above):
- The spectrum looks like this. The noise floor shape is textbook and there is no aliasing of out-of-band signals, but the amplitude is about 11 dB too high.
Receiver configuration takes noticeably longer when the sample rate crosses the 2083334-to-2083335 boundary. This magic frequency is 6.25/3 MHz, which seems more than coincidental.
Re: Sample rate / filtering interaction on the xA4
Posted: Thu Dec 14, 2023 8:46 pm
by adamusa
You can also find documents on how to handle filtering
mapquest directions configuration on xA4 on the websites of FPGA chip manufacturers, such as Xilinx, Intel, Altera,...
Re: Sample rate / filtering interaction on the xA4
Posted: Sat Jan 27, 2024 10:07 am
by pablito1
I had such a thing, a long time tortured with the settings but in the end just bought a new(
https://papas-games.com
Re: Sample rate / filtering interaction on the xA4
Posted: Fri May 30, 2025 2:29 am
by eirajeremy
shc wrote: ↑Wed Sep 20, 2023 4:37 pm
Is there any documentation on how filtering configuration is handled on the xA4? I am using SDRangel as a test bed and am seeing behavior I do not understand. The receiver configuration is shown in the linked images. The input signal is at -60 dBm in all cases.
Sample rate 2083335 Hz and above:
- The spectrum for a 1000.2 MHz signal looks like this. The signal strength is about right, but the noise floor looks strange.
- At 1001.1 GHz we get this. The signal is aliased to ~999.02 MHz and is down by only ~15 dB.
Sample rate 2083334 Hz and below (1 Hz less than the case above):
- The spectrum looks like this crazy cattle 3d. The noise floor shape is textbook and there is no aliasing of out-of-band signals, but the amplitude is about 11 dB too high.
Receiver configuration takes noticeably longer when the sample rate crosses the 2083334-to-2083335 boundary. This magic frequency is 6.25/3 MHz, which seems more than coincidental.
It sounds like you're encountering some interesting behavior with the xA4 and SDRangel. The sample rate transition at 2083334 Hz seems to be a critical point for both filtering and aliasing effects. Have you tried adjusting the filtering settings in SDRangel to see if that impacts the noise floor or the amplitude discrepancies? It might also be worth checking if there are any firmware updates or specific configurations recommended for that sample rate.
Re: Sample rate / filtering interaction on the xA4
Posted: Tue Aug 26, 2025 8:46 pm
by HeadSoccer123
pablito1 wrote: ↑Sat Jan 27, 2024 10:07 am
I had such a thing, a long time tortured with the settings but in the end just bought a new(
Head Soccer
I should probably look for something new too.
