maximum bandwidth on each demod mode

[div...@xtrsystems.com]

I've noticed that the maximum bandwidth available on each demodulation mode is fixed. or example:

raw I/Q - 80 kHz

AM - 80 kHz

FM narrow - 80 kHz

FM mono - 240 kHz

FM stereo - 240 kHz

I would like to increase the maximum bandwidth on the raw I/Q mode - at least to the 240 kHz available on the FM mono and stereo.

Are there any ways to accomplish this (in Gqrx) without building from source? (if even that?)

Joseph

[Jeff Long]

You could try changing PREF_QUAD_RATE in src/receivers/wfmrx.cpp. There is no way to increase this value without rebuilding from source.

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[Vladislav P]

Hello.

As audio sample rate is currently limited to 48ksps, you'll have some aliasing when you set the bandwidth to more than ~45kHz

If you really want to get ~80kHz of bandwidth, then you should either wait, until this PR https://github.com/gqrx-sdr/gqrx/pull/1034 gets merged, checkout and compile this branch https://github.com/vladisslav2011/gqrx/tree/upstream_audio_sample_rate or implement different audio sample rates yourself (submit a PR, please, if you'll do so).

Only after that you'll be able to increase narrowband receiver quadrature rate, update the GUI to increase the bandwidth limit and get as much bandwidth, as you want. Then you'll have a problem getting this wide bandwidth out of your PC as most soundcards have maximum sampling rate limited to 192kHz and even at this "high" rate still apply heavy lowpass filtering.

понедельник, 15 августа 2022 г. в 07:41:05 UTC+3, div...@xtrsystems.com:

[righthal...@gmail.com]

The maximum bandwidth on I/Q data depends upon the sample rate that you save it at. If you save it at 10 MSPS, your maximum bandwidth is 10 MHZ.

The demodulation mode is does not matter. If you want  240 kHz, you need to save the I/Q data at any sample rate greater that 240 KSPS.

[div...@xtrsystems.com]

Thank you all for thoughtful and helpful responses.

It looks like I'm going to learn to build from sources and perhaps await the above mentioned merge.

I've also just completed an install of GNU-radio where I expect to tinker to my heart's content in parallel with the very good Gqrx.

Lastly, I'd like to make a clarification on my comments: I am not (at this moment) looking to increase the final ("audio") sampling rate for this particular project. I am working with FM signals with a varying modulation index (see https://en.wikipedia.org/wiki/Frequency_modulation#Modulation_index) and sometimes greater than that offered standard by Gqrx. A larger modulation index does not necessarily imply a greater sampling rate or final bandwidth; it does mean that the carrier is pushed (deviates) higher and lower to a greater fraction of the carrier frequency. However, higher modulation index does imply higher deviation of the carrier prior to the demodulator and requires the bandwidth to be matched or otherwise adequate. I've got some use cases with the filter function in Gqrx isn't wide enough to catch all the received signal.

Apologies for any confusion I might have caused with my earlier post.

Thanks again. j

[righthal...@gmail.com]

CubicSDR lets you set the bandwidth to any value that you please

[div...@xtrsystems.com]

Thanks for the suggestion. I've grabbed a copy of CubicSDR and find it interesting, useful and a complement to Gqrx which I've already been using. Cubic has given me a reason to learn about SoapySDR and all of that stuff is now installed.

FWIW, I've also realized (and demonstrated) that I can use mono-wideband-FM mode on Gqrx to get what I was looking for originally.  Duh. Well, plenty of learning to do.