gnuradio VS SDRPlusPlus

In gr-dtv transmitter examples for Gnuradio, I see some times people use a resampler block before the RF hardware sink. Say our sampling rate is ~9.14Msps which satisfies the Nyquist criterion because our samples are complex numbers.

2.1. Thanks for that tip, I forgot that I was able to check the source code of the WBFM Receive block. As you have said, there are mostly the same. There are some differences between how values are picked. The WBFM Receive block would be a synonym of Quadrature demod => Fir Filter (decimation => Low pass filter) => FM Deemphasis. 2.3. My question there is why 10 and not 20 or 100. I understand that the idea is to reduce the sample rate asap, but what I don't understand is why those values were picked and how can I understand what would be the "correct" or "best" value. 2.4. I'm not fully understanding what you said. If I check the WB FM recieve source code the values that are supplied as the cutoff freq and transition width of the Low pass filter differ from the one of the example. The webfm would apply a sample rate / decimation / 2 - sample rate / decimation / 32 as a cutoff freq and a sample rate / decimation / 32 as a transition transition width. Calculating those values would end up in different that the ones supplied in this second example. Again, is there a rule of thumb to pick these values?.

Gaussian filter is used only on the tx side, so specifying bt in the receiver makes no sense. Take a look at gfsk mod/demod blocks implementation: https://github.com/gnuradio/gnuradio/blob/master/gr-digital/python/digital/gfsk.py

GNU Radio

Here's the filter coefficients used for the GNU-Radio interpolator block to get you started. This is a 7th order interpolator (i.e., 8 FIR taps) with very good performance. Each "row" of the array sets the delay in steps of sample_time / 128.

From their README: “open-source software development toolkit that provides signal processing blocks to implement software radios.” https://github.com/gnuradio/gnuradio

I'm using newest SDR++ nightly built. win x64. Anyone can resolve this problem? Mabye I'm not using the right driver for SDR++? If so where can I find the right one?

SDR++ from GitHub (https://github.com/AlexandreRouma/SDRPlusPlus) runs on M1

Ah, I see what you mean, it's been a while since I looked at their repo. They don't seem to have one for ubuntu jammy yet in their stable release branch. But they do have an ubuntu jammy one in their nightly builds https://github.com/AlexandreRouma/SDRPlusPlus/releases/tag/nightly. I did give it a go and it seems to work okay, but obviously you would need to try it more thoroughly than I have.

What incompatibility? Do you think that this code https://github.com/AlexandreRouma/SDRPlusPlus doesn't support ARM?

SDR++

Some software tips. There is a newer version of SDR++ that includes an IF filter for NOAA APT signals that should help improve things: https://github.com/AlexandreRouma/SDRPlusPlus/releases/tag/nightly That gives you a new checkbox under the Radio section called "IF Noise Reduction" with a dropdown to select the type of reduction (where you select 'NOAA APT'). You can also use the "Decimation" option in the Source section to give a bit better SNR. From what I've read you get a 3db reduction in noise every time you double the decimation level. If you can't get rid of the noise around 137.1MHz maybe try going for NOAA 15 or 18 since those are at higher frequencies, hopefully away from that noise.