I haven't spent a whole lot of time working with gnuradio. I'm not a
DSP engineer. I am however a software engineer that has dealt with
signals so not completely a laymen, but I am out of my comfort zone.
I had successfully created this project about 4 years ago using Marcus
Leech's Stereo FM Radio implementation and grafting it into the front
design of this the multiple station receiver design. Described here
https://forums.radioreference.com/threads/multiple-fm-station-receiver.341340/#lg=_xfUid-2-1556650274&slide=0
I recorded 2 pirate radio stations at a 4 day music festival. Started
the recording on Thursday. Stopped it on Sunday. The sample rate was
2.4M. I created an Heir block that had the appropriate parts of Marcus
Leech's Stereo FM radio in it. and replaced everything from the xlating
FIR to the multiply const in the second block figure above with the heir
block, and added some WXQT blocks to handle the gui for 2 stations like
wav sinks, file names, etc. It was successful, but one thing that did
happen was I needed to go from a Acer 720 (celeron) with Gallium
installation to an (older) I5 laptop.
I let that project sit for a couple of years. The first thing I did
when I got back to it was upgrade everything. Big mistake... Nothing
worked after that. I got grc 3.10 running with radioconda. I swapped
Marcus's implementation out for Zan's fm_stereo_demod_clean
https://forums.radioreference.com/threads/multiple-fm-station-receiver.341340/#lg=_xfUid-2-1556650274&slide=0
http://zansprojects.blogspot.com/2019/05/stereo-fm-receiving-with-rtl-sdr-and.html
In this new implementation I needed to create a series of variables to
handle the design issue of having the signal be a multiple of 48k for
the audio sink to be the correct speed. In particular the decimations
in the rational resampler.This worked, but when I changed the sample
rate to widen the bandwidth to receive 2 stations further apart on the
FM band than 1Mhz I ran into performance issues. Basically with my
setup the CPU load is about 90% with a sample rate of 1.24 Mhz.
I was able to do this because of the great work done by the people
mentioned above, but figuring out how to deal with the performance
issues is kind of beyond the disciplines I am familiar with. I am
wondering if anybody has any suggestions on how to get
fm_stereo_demod_clean to have better performance. I did not see an
updated version of the Marcus Leech design so I figured there was
something blocking that update, but maybe that is incorrect. I am also
wondering if I could get a more powerful laptop/NUC and make it work
with brute force by throwing money at the project. I would love to hear
any suggestions from people with more grc and dsp experience, or which
path I should take now.
Thanks in advance
Marty
