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Re: [Discuss-gnuradio] DBSRX coherent problem (Phase Noise)

From: tom_wgs
Subject: Re: [Discuss-gnuradio] DBSRX coherent problem (Phase Noise)
Date: Fri, 12 Nov 2010 11:20:17 -0800 (PST)

tom_wgs wrote:
> Hi all
> ...
> ..
> Thank you for your time and any help would be very much appreciated.
> Tom

I have attached a couple additional plots showing the results of taking
128 complex points at 500 kHz sampling rate from channel 2, and dividing
it (complex) by the same number of complex points from channel 1
(element-by-element division, or complex mixing).

If the boards were coherent, you would expect to see a constant value
for the real and imaginary results that represent the static, or short
term, phase offsets between the channels.  Instead, we are seeing that
both real and imaginary output is showing a pseudo-periodic waveform,
suggesting phase imbalance between the real and imaginary, and also
non-coherent behavior.



In some test (3rd image) we see that the real channel is fairly
constant.  If the two receivers had some frequency offset between them,
you would expect to see the real and imaginary parts have a sinusoidal


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