Re: [Discuss-gnuradio] usrp_wxapt_rcv.py

[Patrik Tast]

Hi Bob,

I'm sorry if this is a cross post.

> (NOAA) is 30 kHz but this does not allow for doppler.
Doppler shift at 137 MHz is < 10 kHz and will (should) not be an issue.

I added an pre-amplifier at the antenna and could hear sumthing, though not
enough signal to produce an image.
I found the NB-FM tuner to work best for the BasicRX (after I fiddled with
it some).

A tuned NBFM py, screenshot and recorded audio is at
http://www.poes-weather.com/~patrik/usrp/BasicRX-APT-Test/
I ordered the TVRX daughterboard a few days ago from Holland....

Now my next question:
I got the DBSRX and my intention is to aim a yagi stack at at NOAA-POES and
receive HRPT at 1.7 GHz.
Do you think this is possible?

Thanks,
Patrik

----- Original Message ----- 
From: "Bob McGwier" <address@hidden>
To: "Patrik Tast" <address@hidden>
Cc: <address@hidden>; "Jerry" <address@hidden>
Sent: Thursday, March 26, 2009 11:47 PM
Subject: Re: [Discuss-gnuradio] usrp_wxapt_rcv.py


> 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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> > address@hidden
> > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>
>
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