Re: [Discuss-gnuradio] DBSRX Noise Figure

[Matt Ettus]

Lee Patton wrote:
> This one's for Matt.
> 
> I found a post* where the noise figure of the DBSRX is estimated to be
> between 3 and 8 dB, depending on whether an SNR of 35 or 30 dB is used.
> It also mentions that cable losses were not accounted for in this
> estimate. This was back in May, before the release. Matt, do you have a
> more refined measurement of the DBSRX noise figure now?

I do not have a setup for measuring noise figure in the standard way.
Using a signal generator and the usrp_fft.py application you can
determine the approximate level of the noise floor in the bandwidth of
an FFT bin.  From there you can calculate the noise floor in Watts/Hz.
The ratio of that to kT gives the noise figure.  I am able to measure a
typical NF of 5-7 dB.  This includes cable loss, so if you figure about
1dB of loss, you get a NF of 4-6 dB.

A useful application would be to control a calibrated noise source and
measure the power in a given bandwidth with it on and off.  This is how
a noise figure meter works.

Matt