Re: [Discuss-gnuradio] Different sensing results with same hypothesis

[Dan CaJacob]

I don't think there is any AGC on USRP hardware...

Very Respectfully,

Dan CaJacob

On Wed, Feb 19, 2014 at 9:57 AM, Aditya Dhananjay <address@hidden> wrote:

On Wed, Feb 19, 2014 at 6:26 AM, Lebowski80 <address@hidden> wrote:

Hello everyone,

Before to explain my problem I give some technical information about my
hardaware. I'm using USRPs v1 and the boards integrated are XCVR2450
Transceivers.

I'm using the script usrp_spectrum_sense.py in a USRP to detect a signal in
a ISM channel. To have a signal expressed in db I did this simple operation
to the received signal:

signal_db = 20*(math.log10(math.sqrt(m.data[0]/tb.slot_number)))

I can control the signal transmitted in the ISM channel; so, I know exactly
the time when there is a signal to be detected in the channel. During the
first hours the USRP detects the signal giving me a value of around 40 db
but after some hours such a detected signal decreases up to roughly 10 db
and it does not change anymore regardless of the signal transmitted in the
ISM channel. Only if I kill the process running the usrp_spectrum_sense.py
script and execute it again, the USRP starts to detect again the 40 db
value. The signal to be detected in the ISM channel is always the same. Can
anyone tell me which is the problem?

Thanks in advance.

I have no clue, but my first (and only) guess would be the automatic gain control (AGC) on the USRP hardware.

If you figure it out, please let us know!

best,

aditya

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