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Re: [Discuss-gnuradio] strange receiver behaviour with UHD

From: Nick Foster
Subject: Re: [Discuss-gnuradio] strange receiver behaviour with UHD
Date: Tue, 28 Sep 2010 09:53:09 -0700

It's likely that initialization of the board gain and frequency settings
will take some finite but non-zero amount of time to settle. It's always
a good idea to toss the first few samples until things settle down. The
settling time will be different for each daughterboard and should be
experimentally determined in your application.


On Tue, 2010-09-28 at 15:15 +0200, Patrik Eliardsson wrote:
> Dear List,
> We have made a test program using a source and a file sink (see fg.jpg) where 
> we are receiving a fixed number of samples (with UHD and USRP2 and WBX-card) 
> from an AWGN-generator (constant power -19dB).  If we plot the abs value of 
> the received signal we always see a "spike" in the 10 first samples (see 
> fig1) before the abs value settles to a more expected value. Sometimes 
> (seldom) there is no "spike" but the result is still not as expected, the 
> received data starts at a higher level and slopes down during a quite long 
> time before settling to a stable level (see fig 2).
> Have we missed something or why does this "spike" occur? Is there some 
> initialization time in the hardware that we need to take into consideration 
> before we start to receive samples (recv) after setting all parameters?
> Br,
> Patrik 
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