[linrad] Re: PCM2900 sound chip in Linrad

[Cynthia Lyons <earthlink.net; sealions@xxxxxxxxxxxxxxxx>]

Leif,
     The PCM2900 has a design defect so that one channel is a clock 
tick later on the usb line to the computer.
Sorry I didn't make it clear.  I have played with small corrections in 
amplitude and phase.
  Actually in Winrad, I did the 1 clock shift and the fine adjustments, 
and never got the image at negative frequency to be less than 15 db 
lower than the main signal.
David Underwood

Leif Asbrink wrote:
> Hi David,
>
>   
> > I have not yet found how to set up Linrad to compensate for one channel 
> > of a sound card having a delay. The PCM2900 chip seems to have this problem.
> >     
>
> A delay difference between I and Q will cause a phase error that grows 
> linearly with frequency. In Linrad there is a calibration procedure that
> will compensate for an arbitrary variation with frequency of both phase 
> and amplitude errors. The reason is that anti-alias filters (such as 
> those used in the WSE units) would be extremely difficult to match 
> between the channels. The calibration should take care of the delay
> so there is no feature in Linrad to treat it as a special case.
>
> 73
>
> Leif / SM5BSZ
>
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