Hello J,
You can find some details on this at URL: http://radioware.nd.edu/documentation/basic-gnuradio
It sounds like much of this will be old hat to you, but there is a
section entitled "Exploring the FM receiver," which addresses at least
some of your specific question.
Sincerely,
Dan Marlow
On Jul 10, 2011, at 9:07 PM, concernedconsumer wrote:
Hello,
I am a high school student and am very interested in the AM and FM
demodulation processes. I have been using gnu radio in combination
with a USRP to receive radio signals, demodulate, and listen. This
past year, I worked through the details of AM demodulation in gnu
radio by computing mixing, low-pass filtering, decimating,
interpolating, and normalizing algorithms. This helped me better
understand the AM demodulation process, and especially what was
being done in each of the gnu radio blocks. I am now trying to do
the same thing with FM demodulation and have implemented the
following; frequency x-lating FIR filtering, calculating the
instantaneous frequencies, and decimating and interpolating routines
(as performed in the rational resampler).
My question is about the instantaneous frequencies in FM
demodulation. I know that the frequency of the carrier varies with
the strength of the transmitted signal. The instantaneous
frequencies must then be the deviation of the modulated signal from
the carrier (which is at baseband) and denote changes in the
strength of the transmitted signal. Still, I must be missing some
steps that are performed in the WBFM block. After I calculate the
instantaneous frequencies, what do I have to do to complete the
demodulation process and be able to play the file back through the
audio sink? I have attached a screenshot of the gnuradio-companion
flow graph I am following, along with a pdf of the process I am
implementing.
What does the WBFM block do, mathematically, to the signal? I would
also appreciate feedback on the process I am using.
Thanks,
J
<
screenshot_grc
.png
><FM_demodProcess.pdf>_______________________________________________
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Daniel R. Marlow mar...@princeton.edu
Homepage: http://wwwphy.princeton.edu/~marlow/
Phone: 609 258 4383 Fax: 609 258 6360
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