> Date: Tue, 16 Mar 2010 16:54:34 -0400
> From: [email protected]
> To: [email protected]
> Subject: Re: [ivtv-users] hvr-1600, frame CRC mismatch - incomplete frame
>
> On Tue, Mar 16, 2010 at 4:22 PM, Kyle Lil <[email protected]> wrote:
> > Interesting. It looks like the error rate is ~1 per 25 minutes with qam_gain
> > set to 0x01 and the weak SNR (0x140). With the qam_gain set to 0x02 and the
> > weak SNR (0x13c), the error rate is back to ~2 per minute.
>
> Ok, so you described the behavior with the weak SNR. What about with
> the strong SNR?
>
> > So it seems that the error rate is more related to the qam_gain setting
> > than the SNR.
>
> Without knowing the behavior with a strong SNR, I cannot confirm or
> argue against this conclusion. It's possible that you will see the
> opposite behavior with a strong SNR (where you get fewer errors with
> the gain set to 0x02).
>
> > I was
> > actually just taking a shot in the dark by changing this parameter. Could
> > you tell me what it actually does? Is this related to AGC gain somehow?
>
> Not without both of us having a degree in applied signal theory. :-)
>
> It's a tuning value for controlling the gain when in QAM mode. On the
> mxl5005s it is typically set based on the selected target frequency.
> However, because of the combination of the mxl5005s and the s5h1409 as
> well as some nuance of the PCB layout of the HVR-1600, it's always
> hard-coded to 0x02. Basically, by hard-coding the setting to 0x02
> (instead of making it frequency dependent as per the mxl5005s
> datasheet), we duplicate the behavior in the Windows driver (the
> engineers at Hauppauge arrived at that conclusion after using
> equipment significantly more expensive than what's in my budget).
>
> I keep asking about the error rate and effects of changing the gain
> relative to the SNR because I'm wondering whether there is some
> optimization I can put in there where I base programming of the the
> gain level on the final SNR.
>
> Devin
>
> --
> Devin J. Heitmueller - Kernel Labs
> http://www.kernellabs.com
>
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OK for me, the stronger signal gives a similar result to the weak signal. If
anything, the improvement in SNR appears to be a bit greater. With qam_gain set
to 0x02, the SNR is 0x140 and the error rate is about 1 error every 30 seconds.
With qam_gain set to 0x01, the SNR is 0x146, and the error rate is
approximately 1 every 25 minutes.
It's interesting to learn that the Windows driver hard codes this value to 0x02
since I get no noticeable errors in Windows. It's also interesting that the
qam_gain should, in theory be set to a different value for different
frequencies. Up to this point, I've been using one channel for all my tests.
I'll try different channels to see if there are any for which qam_gain=0x02
works better.
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