[Discuss-gnuradio] Re: Spurious Spikes Seen with usrp_fft.py

[Thomas]

Robert Fitzsimons wrote:

Date: Sun, 20 Jan 2008 12:57:57 +0000
From: Robert Fitzsimons
Subject: Re: [Discuss-gnuradio] Spurious Spikes Seen with usrp_fft.py
To: address@hidden
Message-ID: <address@hidden>
Content-Type: text/plain; charset=us-ascii

Hi Thomas

You email never made it into my mailbox, maybe it got caught as spam.

> I am using a USRP with only a DBSRX daughterboard installed. The image
> at the following link is a screen capture I took.
> http://img340.imageshack.us/img340/3570/screenshotusrpfftfy8.jpg
> Does anyone know why the spike at 921.6 MHz is there?

The spike doesn't look like it's from a GSM base station. What country
are you in? Have you tried tuning the usrp_fft.py to the 921.6 MHz
signal?

> I have observed many of these spikes in other parts of the spectrum
> using usrp_fft.py. I looked for them using a real spectrum analyzer
> connected to an antenna and did not observe them.

Maybe your USRP is picking up some interference, can you try it with a
different computer and with a different power supply?

Robert

Thanks for you reply, Robert.

I am in the U.S. 

I have used usrp_fft.py to tune to 921.6 MHz, and the spike is still there at 921.6 MHz. 

I tried powering the USRP from batteries, but the spike was still there. It was also still there using a different
 computer. I tried using a USB cable with a ferrite bead, but it didn't change anything.

I positioned the USRP very close to the antenna connected to a real spectrum analyzer, and I was able to observe the spike on the spectrum analyzer. I guess the USRP is actually radiating this frequency. It might go away if I place the USRP's antenna farther away from the USRP itself, which I haven't been able to try yet.

Does anyone know what the source of this might be within the USRP? I don't believe this will cause me any problems. I'm really just curious. 

Thanks,

Thomas

---

Never miss a thing.   Make Yahoo your homepage.