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

From: tom_wgs
Subject: Re: [Discuss-gnuradio] DBSRX coherent problem (Phase Noise)(partial solution! Charge Pump)
Date: Sat, 13 Nov 2010 10:41:13 -0800 (PST)

tom_wgs wrote:
> 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).
> ....
> ...
> .
> http://old.nabble.com/file/p30202507/Time%2BDomain%2BFreq%2B%2526%2Bother%2Berrors.jpg
>  http://old.nabble.com/file/p30202507/RXA_norm_RXB_Time_Domain.jpg 

I found a partial solution but am not sure why and if my problem is
completely fixed.  I found that the Charge pump setting (_set_cp(int) was
being set to 2 different values at 1880mHz for the 2 receivers.  After
experimenting the best results come when forcing the values both to 1 for
all tested frequencies.

The results can be seen below.  Compare this to the results previous
provided above.   Can anyone provide some information on the charge pump and
how the settings effect the receiver.


Some results at 1880 mHz.

Results at 826 mHz

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