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

Dan CaJacob dan.cajacob at gmail.com
Wed Sep 4 09:17:01 EDT 2013

Try some Amateur satellites - they may have their TXs on more often.  I
regularly use USRPs with Yagi antennas to work LEO passes with my own birds.

On Wednesday, September 4, 2013, Marcus Müller wrote:

>  Hi Ruoyu,
> I'm not really surprised you don't see GPS - it's a spread spectrum
> system, and power levels (let's say a GPS satellite transmits 1kW == 60dbm;
> free space loss should be around 182dB for a 21e6m distant satellite on
> 1GHz...) can be indistinguishable from noise; not seeing this in an FFT
> plot is totally ok, even with your high end setup.
> I've got no knowledge on Iridium, however. This should be a TDMA/FDMA
> system, and might be (due to low power, a quick google turned up 400W per
> satellite, low duty cycle due to no active terminals where you are)
> undetectable by looking at an FFT plot, too.
> So basically: With your high-end setup you're aiming to find things that
> are to weak for the unequipped eye(antenna); you will therefore most
> probably never see anything on your FFT plot. Employ your RF comm knowledge
> and specialized sensing techniques (correlation for GPS etc), and you
> should get better results.
> Greetings,
> Marcus
> On 09/04/2013 09:40 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
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Very Respectfully,

Dan CaJacob
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