gnuradio VS noaa-apt

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

GOES sats are geostationary but the NOAA APT satellites are encircling the planet and you can pick them up. Old tutorial but still relevant, just use "noaa-apt" tool[0] instead of WXtoImg. https://www.rtl-sdr.com/rtl-sdr-tutorial-receiving-noaa-weat...

[0] https://github.com/martinber/noaa-apt

Sometimes WXtoIMG just discards parts of the recoding when the signal wasn't strong enough. In those cases I've had some luck running the recorded .wav file through noaa-apt to get the full image.

so the NOAA_APT decoder link on your guide did not work properly, By chance did you mean this link https://noaa-apt.mbernardi.com.ar/?

So far I only use it for noaa-apt program though.

Had this exact problem, the thing that I found is that GQRX records at the wrong sample rate, which WXtoImg can’t handle. However, https://noaa-apt.mbernardi.com.ar this utility did work for me. I’ll also note that WFM is the setting I use in GQRX, not AM

You should try noaa-apt too, it usually gives better results for me.