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

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] strange receiver behaviour with UHD
Date: Tue, 28 Sep 2010 13:34:33 -0400
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20100907 Fedora/3.0.7-1.fc12 Thunderbird/3.0.7

> 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.
> --n
Yup, and I'd like to point out that this isn't just a "quirk" of this
particular hardware.  All such hardware takes a finite amount of time
  to "settle" -- the synthesizers often take a handful of milliseconds
to settle to their final value, and even VGA settings take finite time.

The A/D has no way of knowing what that time is, so it starts sending
samples right away--those samples will contain "artifacts" of
  whatever settling has to take place.  Fact of life.

I don't know how the filters in the FPGA are coded, but it also wouldn't
surprise me if they take some finite amount of time to converge
  on correct output, since they'll have some indeterminate startup state.

Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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