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: discuss-gnuradio@gnu.org
Message-ID: <[EMAIL PROTECTED]>
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
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