[linux-dvb] More on the cx24123

Vadim Catana vcatana at registru.md
Wed Mar 22 07:03:42 CET 2006

Yeasah Pell wrote:
> I've done some more testing, and I feel much more confident about my 
> theory on the cx24123 bands. From my testing, I believe that the tuner's 
> VCO #8 has a center frequency around 2300MHz, and is only useful when 
> using the /4 divider (so there are effectively only 9 band selects, not 
> 10). I think the datasheet is essentially correct in terms of showing 
> individual band ranges, it just mixes up the assignments.
> Also, I did confirm that I can tune low symbol rate signals using the 
> original spec'd VGA offset values from the spec if the demodulator 
> sample gain is set correctly.
> I did also do some experimentation to determine the behavior of the 
> demodulator's frequency search capability, and it definitely does do 
> some of that, and can be controlled with the range and initial frequency 
> parameters, but I haven't quite nailed down the exact behavior (for one 
> thing, it looks more like +/-4MHz instead of the advertised +/-10MHz). 
> The final thing I want to figure out before I'm satisifed with the 
> performance of the driver is the interaction between the demodulator's 
> frequency search and the linux dvb software zigzag.
> I haven't gotten any comments on any of this so far -- is anybody 
> actually interested in these improvements? I have no idea if this is a 
> common card or not.

Could you send a patch with your changes to the list, so that we could
test them? I'm particularly interested in the changes to the demodulator
sample gain. I have tried different settings of that, but without
changing the VGA offset values the card did not tune well to signals
with low symbol rates.

Vadim Catana

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