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From: | Matt Ettus |
Subject: | Re: [Discuss-gnuradio] USRP / DBSRX calibration |
Date: | Wed, 26 Dec 2007 14:25:04 -0800 |
User-agent: | Thunderbird 2.0.0.9 (X11/20071115) |
Replying a bit late here... Jens Elsner wrote:
As Eric Matlis a while ago (see link to thread at the bottom), I would like to calibrate my USRP/DBSRX combination for measurements. As noted, the USRP is not a measurement device, but nevertheless I'd like to give it a try. My application are GPS based measurements in the GSM downlink band. 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 lossaccounted for
That's a lot of cable loss. Are you sure its that much?
Offset (to convert from dB to dBm): -177.7 Noise floor: -112.5 dBm, sensitivity -165 dBm/Hz (NF: 8.7 dB at 20 degrees) Linear measurement range: -100 dBm to -50 dBm 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.
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.
Matt
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