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Re: [Discuss-gnuradio] DBSRX Noise Figure
From: |
Matt Ettus |
Subject: |
Re: [Discuss-gnuradio] DBSRX Noise Figure |
Date: |
Tue, 29 Nov 2005 22:03:53 -0800 |
User-agent: |
Mozilla Thunderbird 1.0.7-1.1.fc4 (X11/20050929) |
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