Re: [Discuss-gnuradio] usrp_wxapt_rcv.py

[Johnathan Corgan]

2009/3/21 Patrik Tast <address@hidden>:

> I fired it up today to test the BasicRX side using the usrp_wfm_*.py and
> nbfm and everything works as expected. I am able to hear what ever FM
> channels with great quality.

> NOAA 17 @ 137.62 MHz was here just (usrp_wxapt_rcv.py -f 137.62e6 -V 0) and
> all I could hear was German radio comming through. Extremly faintly, I could
> hear the TICK-TOCK sound in the background (I also could have been
> imagining, it was so unclear) and (just) some change in the graph while the
> satellite was over me (45 degrees).

I suspect you're just seeing the effect of vastly different signal
strengths and a receive daughterboard with no filtering or gain.

Broadcast band FM station power is measured in kilowatts or tens of
kilowatts, and result in high signal levels at the BasicRX input.
These are easy to demodulate.  However, the APT transmissions are
likely several orders of magnitude lower in level at the antenna
input, and without any filtering or gain, probably don't rise above
the noise floor of the ADC.

At 137 MHz, you should be using the TVRX daughterboard which is based
on a VHF/UHF cable TV tuner, and provides the right sort of
prefiltering and receiver gain to successfully decode APT.

Johnathan