[ivtv-users] hvr-1600, frame CRC mismatch - incomplete frame

Kyle Lil kpl388 at msn.com
Tue Mar 16 19:46:14 CET 2010

> Date: Tue, 16 Mar 2010 14:12:36 -0400
> From: dheitmueller at kernellabs.com
> To: ivtv-users at ivtvdriver.org
> Subject: Re: [ivtv-users] hvr-1600, frame CRC mismatch - incomplete frame
> On Tue, Mar 16, 2010 at 1:45 PM, Kyle Lil <kpl388 at msn.com> wrote:
> > I just wanted to give a quick update in case anyone else is experiencing the
> > same problem as me. I was able to reduce my glitch rate from about 2 per
> > minute to approximately one every twenty minutes by changing the .qam_gain
> > parameter in cx18_dvb.c from 0x02 to 0x01. Does anyone know what this does
> > physically? Does this offer any insight as to what could be done to
> > eliminate the remaining errors?
> >
> > Best,
> > Kyle
> Yeah, the mxl5005s has a pretty messy RF profile with regards to
> finding the optimal tuning conditions that work properly for both
> strong and weak signals.  It's not too surprising to find that
> adjusting the gain could yield different results.
> Can you please provide the SNR data for the both values of the
> qam_gain (so I can see if you've got a strong signal or a weak one?).
> In other words, do an azap, save the results, then change the qam_gain
> and do another azap and save the results.
> Thanks,
> Devin
> -- 
> Devin J. Heitmueller - Kernel Labs
> http://www.kernellabs.com
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With cables/splitter arranged in a configuration to give the HVR-1600 a stronger signal I see an improvement in SNR from ~0x146 to ~0x14a when I change qam_gain from 0x02 to 0x01. Rearranging connections to provide the HVR-1600 a weaker signal, I see a similar improvement from 0x13c to 0x140 when changing from 0x02 to 0x01. In both cases the SNR appears stable, never changing by more that 0x002. 

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