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[Discuss-gnuradio] FM demodulation block performance ?
From: |
jmfriedt |
Subject: |
[Discuss-gnuradio] FM demodulation block performance ? |
Date: |
Thu, 7 Mar 2013 17:19:06 +0100 |
I am still trying to receive NOAA APT signals using the RTL-SDR DVB dongle.
What I did
so far:
1/ using a wideband discone antenna, I receive the NOAA APT characteristic
signal during passes
on a AOR3000 scanner. I know the NFM mode of the AOR3000 is too narrow for full
decoding of the
image (saturated whites), but at least I know my antenna is good enough to
recover an audible and
usable signal,
2/ on the antenna I put a splitter (Minicircuits ZFDC-10-5) with 10 dB loss on
the coupled output
(to the AOR3000) and 1.5 dB loss on the direct path (to the DVB receiver).
3/ I use http://picasaweb.google.com/lh/photo/2QDS5vwPra5Q7yQbSdUOng as an
example of NBFM receiver
usage (extending the demodulation bandwidth to 30 kHz instead of the 5 kHz in
the example), or I
try a WBFM receiver module with a 30 to 40 kHz bandwidth, both of which were
preceded by a 100-kHz
low-pass filter (either as in the screenshot using the FIR coefficients in a
Xlating block,
or using the LPF block)
In all cases I get a clear signal on the AOR scanner (even after the 10 dB loss
on the coupler) while
I cannot recover any usable signal on the DVB receiver, with RF gains in the 33
to 39 dB range and
IF gains in the 25 to 40 dB range. A friend of mine got usable signals using
the NFM demodulator from
SDRSharp (which I have not yet managed to get running) with the DVB dongle.
Any idea whether the FM demodulation blocks require some minimum signal to
noise ratio to lock ?
more generally is there any other description/documentation on the blocks other
than the doxygen
generated information and source codes ?
Thank you, Jean-Michel
--
JM Friedt, FEMTO-ST Time & Frequency/SENSeOR, 32 av. observatoire, 25044
Besancon, France
- [Discuss-gnuradio] FM demodulation block performance ?,
jmfriedt <=