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Re: [Discuss-gnuradio] Re: Frequency dependent problem after syncronizin


From: Eric Blossom
Subject: Re: [Discuss-gnuradio] Re: Frequency dependent problem after syncronizing , Please help!
Date: Mon, 16 Feb 2009 12:55:14 -0800
User-agent: Mutt/1.5.18 (2008-05-17)

On Thu, Feb 12, 2009 at 02:17:05PM -0800, Johnathan Corgan wrote:
> On Thu, Feb 12, 2009 at 1:20 PM, Bruhtesfa Ebrahim <address@hidden> wrote:
> 
> > What makes it strange is the dependence on gain.when the linear gain in
> > the spectrum panel(usrp_fft.py)is set to 0,the signal at the center(the
> > DC)is 5dB higher than the noise level.When I increase the gain, the
> > difference between the DC and noise level keeps decreasing and finally
> > the DC level is equal to the noise level.
> > Specifically, for a linear gain >=20, the signal around DC is not
> > visible(it is equal to the noise level).
> 
> Actually, what you're now describing is more like not receiving any
> signal at all--the small line at DC is residual DC offset from the
> ADC, and the noise is simply that, noise that gets amplified according
> to the gain setting.  At a certain point the noise power exceeds the
> small DC offset.
> 
> Johnathan

Agreed about no (or low) signal, though I think the small line at DC
is a truncation artifact in the FPGA. 

Eric




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