[USRP-users] How to use N210 to detect and collect weak satellite signals

Marcus D. Leech mleech at ripnet.com
Wed Sep 4 10:06:05 EDT 2013


On 09/04/2013 03:40 AM, Li Ruoyu wrote:
> Hi, All
> I am working on a project which requires to receive signals from LEO 
> satellites like orbcomm and iridium.
> I tried to use USRP N210 to collect the data, but I found the signal 
> may be too weak to be observed.
> Stuffs I used:
> 1. USRP N210, DBSRX2 800-2400MHz
> 2. /Minicircuit/ cable amplifier, provides 37 dB gain at 15V/0.68A 
> supply input. To ensure signal is enough enhanced, I used two of them 
> in recent experiments.
> 3. Horn antenna with frequency range from 0.8 - 18 GHz. beamwidth 60 
> degree.
> After connected all things and warming up, I run "uhd_fft" to check if 
> signals can be seen in frequency domain. I expected a peak around the 
> center frequency. However, it is just noise. But if I turned center 
> frequency to GSM band, it showed signal clearly. And then I turned it 
> to 1.57542 GHz, which is the L1 band of GPS, it also shows nothing but 
> noise.
> So, I am wondering if it is because the signal it too weak to be 
> detected in that way.
> Have anyone ever done weak signal detection and collection before with 
> USRP ? not only satellite, any weak signals is fine.
> If you have done similar project before, could you please tell me how 
> you know signal is there if it cannot be seen by FFT. Any other 
> function can help ?
> Many thanks ahead.
> Best regards,
> Ruoyu
>
You've received other comments about correlation for GPS, etc.

What you haven't mentioned is the use of an LNA right up at your 
feedhorn.  That minicircuits cable amplifier will not be an LNA.  The 
noise figure
   of the first gain stage is *critical* in being able to 
detect/demodulate weak signals.




-- 
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

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