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Re: [Discuss-gnuradio] PSD in dBm/Hz

From: madengr
Subject: Re: [Discuss-gnuradio] PSD in dBm/Hz
Date: Thu, 5 Mar 2015 08:09:04 -0700 (MST)

Do you mean adding a text label on the vertical axis, or scaling the
spectrum?  For the latter, you would have to feed the USRP a known
(calibrated) noise source that is well above the USRP noise floor such as an
HP 346 noise source.  Then read the value from the spectrum and just
re-scale the samples to your known PSD.  If you change the FFT bin size,
decimation, tuning, etc, you may need to re-scale.

I suppose you could also feed the USRP with a CW tone of known power to
figure out it's gain, then terminate the input with 50 ohms (i.e. -174
dBm/Hz) and measure the power (which would be -174 dB/Hz + NF + gain).

In either case, you need a known power source to convert the dB to dBm, and
noise to fill your bandwidth to get the 1/Hz.  


activecat wrote
> I am using USRP to receive signal, and then plot the signal using "WX GUI
> FFT Sink".
> I hope to get the vertical axis as "Power Spectral Density in dBm/Hz".
> Is there any way to do that?

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