I am the author. The bandwidth of the signal transmitted from the APT
satellites (NOAA) is 30 kHz but this does not allow for doppler.
The basic RX is almost wholly inappropriate for NOAA APT and for
anything band pass sampling application without appropriate filtering.
Operating a 60-ism MHz sample rate A/D means the Nyquist frequency is
30-ish Mhz. So all of the signals you are talking about are done with
undersampling, using aliasing. But, FM transmitter are extremely
strong. APT are NOT. All of the noise that is in every 30-ish MHz
segment up and beyond are folded down on top of the signal of interest.
This is less important in FM than in weak signal satellite work.
I never considered that anyone would do this or I would have tested for
the presence of an appropriate tuner or an override be asserted.
Bob
Patrik Tast wrote:
Hi All,
My name is Patrik Tast from Vasa, Finland.
I this week received the Ettus USRP with daughterboards BasicRX and
800-2400 MHz RX from CA, US.
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.
Since I am a wxapt guy, http://www.poes-weather.com/, the
usrp_wxapt_rcv.py was my next test in the examples directory.
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).
When I changed to the R2FX-receiver (dedicated APT-receiver) the
signal is there http://www.df2fq.de/english_version/r2fx_eng.html
I could not find an author to the usrp_wxapt_rcv.py nor could I find a
GRC block diagram for it.
I can see that the author is aiming for 32 kHz bandwith but I suspect
there is something missing?
APT spec is at http://www2.ncdc.noaa.gov/docs/klm/html/c4/sec4-2.htm
I'm using Fedora 9 and GnuRadio 3.1.3 (latest stable release, not from
svn)
Any help appreciated,
Thanks,
Patrik
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