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

[Per Zetterberg]

On Tue, 2010-09-28 at 13:34 -0400, Marcus D. Leech wrote:
> >
> > 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.
> 
> 

My experience is that it doesn't matter how long I wait after setting
the gain and frequency. 


It could be FPGA filters.

BR/
Per