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Re: Working Narrowband FM examples?

From: Nathan Van Ymeren
Subject: Re: Working Narrowband FM examples?
Date: Wed, 4 Aug 2021 10:40:30 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0

Hi Mike,

That's exactly what I was looking for, thanks.

However:  I swapped out the USRP source for an osmocom source, and it seems to be "mostly working" but the audio comes through like the adults from the old Charlie Brown show from when I was a kid.  Instead of clearly-intelligible speech like I can hear through GQRX, using gnuradio I can only get speech that sounds like "mwah mwah mwah mwah"

Attached is a .png of my flowgraph, hope it's not too large for the list (about 100kB).

Appreciate any advice anyone might have.


On 8/3/21 3:47 AM, Mike Markowski wrote:

When I was refreshing my gnuradio awareness - I hesitate to use the word "skills" :-)  - I ran through the official tutorials and modified them as needed to work with a usrp b210.  On the page


about halfway down is the title "Gnuradio Official Tutorials" with the link "Here are my versions" where you'll find nbfm.grc.  It's very simple, using filter/squelch/NBFM Receive block and runs here on grc, a promising sign.

Hope it's useful,

On 8/3/21 2:40 AM, Nathan Van Ymeren wrote:

I am seeking a working NBFM receiver example, as the one on the wiki[0] produces unintelligible output.  I am confident that my hardware is functioning properly because if I tune to the same frequency (162.525 MHz ) in gqrx, I can hear the weather radio broadcasts clearly.  I am on OpenSUSE Tumbleweed, running gnuradio 3.8.x with a HackRF One and a standard telescopic antenna.

I have reproduced [0] verbatim except with the following change:  Instead of a ZeroMQ source, I am using an osmocom source for my hackrf.

I’ve also tried adapting the flowgraph from the “SDR with HackRF” tutorial[1], which implements a wideband FM receiver in gnuradio, but I wasn’t able to make it produce anything resembling speech when I changed it to narrowband FM.

Additionally, I’ve tried a few NOAA weather radio flowgraphs found online but most of what I’ve found either didn’t work or else was for an older version of gnuradio and thus had errors that I wasn’t able to work around since I am a gnuradio novice.

Can anyone recommend a working flowgraph for narrowband FM, ideally something simple and working in gnuradio 3.8+?



[0] https://wiki.gnuradio.org/index.php/Simulation_example:_Narrowband_FM_transceiver#NBFM_receiver
[1] https://greatscottgadgets.com/sdr/1/

Attachment: nbfm.png
Description: PNG image

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