I want to experiment with digital protocols in ham
radio by starting with the PC soundcard. I understand some of the basics like
filters and FFT. I even have some of them working in code (C++).
I do not know how to proceed from the basics into
demodulating an audio signal into bits.
For instance, I am playing with the VHF packet
protocol which use 1200 and 2200 hz signalling. I enter the samples for a single
1200 hz cycle into the FFT array. The FFT shows a peak at around 1000 hz. The
FFT array is 2048 samples long filled with 0s except for the 1 cycle of
1200 hz which is 40 samples at the rate of 48000 samples per second. If I put 4
cycles in the FFT array I get 1195 hz which is correct. Hanning or Hamming
Windows do not help.
I have looked at some of the available source but
am missing the insight I need for proceeding further. Any suggestions on how to
proceed further? Any suggestions on books or web sites that address
communications DSP at this level? How about an email reflector where I can ask
questions of DSP gurus?
-73-
Rud K5RUD
ARES AEC Montgomery County, TX Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) YAHOO! GROUPS LINKS
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- [digitalradio] RF Digital Protocol Education Rud Merriam
- Re: [digitalradio] RF Digital Protocol Education Nick Fedoseev