FM demodulation block performance?

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

On 07 Mar 2013 11:19, jmfriedt wrote:

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

Your FM demod blocks are configured for
quadrature-rate == audio_rate This doesn’t work very well. I generally
have the quadrature rate be some small multiple (2 or 4) of the audio
rate.

Look at the way multimode, for example, handles NBFM
demodulation for various “standard” NBFM bandwidths.

This forum is not affiliated to the Ruby language, Ruby on Rails framework, nor any Ruby applications discussed here.

| Privacy Policy | Terms of Service | Remote Ruby Jobs