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 mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
