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Re: [Discuss-gnuradio] USRP / DBSRX calibration
From: |
Jens Elsner |
Subject: |
Re: [Discuss-gnuradio] USRP / DBSRX calibration |
Date: |
Wed, 26 Dec 2007 23:44:00 +0100 |
User-agent: |
Mutt/1.5.13 (2006-08-11) |
Matt,
thanks for your reply.
> >Using a noise generator, I came up with the following figures:
> >
> >USRP settings: DBSRX, gain 52, decimation factor 32
> >Calibration bandwidth: 190 kHz around center frequency, 3dBm cable loss
> >accounted for
> >
>
> That's a lot of cable loss. Are you sure its that much?
The figure I posted was wrong, it was actually 1.3 dB.
> >I noticed that (with gain 52) the USRP goes into saturation above -50
> >dBm and does not quite show linear behaviour below -100 dBm.
> >
> Not sure what you mean above. With gain of 52, the system gain is
> pretty high. For a strong signal like -50dBm you would want to have a
> lower gain.
I was trying to measure signals starting at roughly -100 dBm (400kHz).
That's why I chose a high gain. The "saturation effect" I'm seeing
around -50 dBm might well be due to numerical limitations of the
algorithm (integral over PSD estimate) used to calculate the power in
the band. I have to check on that again.
Should I be able to measure linearly over more that 50 dB dynamic range
with the USRP/DBSRX combination?
> >Furthermore, -165 dBm/Hz is a better sensitivity than my spectrum analyzer
> >offers, which I find rather odd. Do these figures make sense?
>
> Spectrum analyzers rarely have good noise figures. -165dBm/Hz
> translates to a roughly 9dB noise figure, which is a little high for the
> DBSRX, but not unreasonable. It is better than my spectrum analyzer.
Thank you very much for that insight. I was rather suprised, given the
20dB$ price difference.
Jens