[linux-dvb] TDA10086 (TT S-1401) DiSEqC problem

Hartmut Hackmann hartmut.hackmann at t-online.de
Wed Dec 20 23:00:10 CET 2006


Hi, Chris

Chris Malarky wrote:
> Hi Hartmut,
> 
> On Mon, 2006-12-18 at 22:49 +0100, Hartmut Hackmann wrote:
> 
>>Regarding the signal strength:
>>Vladimir Monchenko just proposed a patch below.
>>There also is a patch regarding the DiSEqC. I got another patch for
>>review. I will attach it. Please note that it is reverted.
>>Can you please test these and report the results. If you say they are ok,
>>i will integrate them.
> 
> 
> OK, firstly I followed Vladimir's idea to invert the reported signal
> strength and quality.  This seemed to make sense as we were getting 20%
> signal strength under Linux, against 84% under Windows.
>
Well, the explaination does not make sense but i can confirm that Vladimirs
patch is at least basically right. A note:
I have no idea how the windows driver reports the signal strength so i can't
tell whether it makes sense to compare these values. But the current tda10086
driver reports the analog AGC level as signal strength. This is not perfect.
I currently have the same in the tda10046 driver: if the signal is weak but ok,
you can have a stable lock at the signal stregth 0 - which sounds odd but i
could observe this. It would be better to build a weighted sum of AGC level
and IF signal amplitude.

> I then applied the two patches you sent.  This then gave me a drop in
> the reported signal strength by ~20%.
> 
This might be right....

> Can you explain what the patches are actually doing?  And perhaps any
> other values I might try to tweak the signal any more?
> 
> Do you have access to datasheets for this card?
> 
Yes, i have access to the datasheets of tda10086 and tda8263. Unfortunately,
they fall under a NDA, so i can't post them here.

What the patches do:
- The patch for the tda10086 changes the parameters of the carrier recovery
   loop. This has no impact on the signal strength but on locking / raw ber
   with poor signal guality.
- The patch for the tda8263 modifies the IF lowpass filter (byte 5) and
   a gain correction stage (byte 6)
I guess that the sencond patch has impact on the signal strength readout.
But it can still be correct: As far as i can see, the bandwidth setting is
correct and the gain setting might be necessary to make the tuner work under
all circumstances.
In january, i can try to get an appnote or i can talk to the developers of
the windows driver to get more information.

When you judge the patches, can you please watch the raw ber? There can
easily be situations where you get a higher signal strength but a worse
ber - and the latter is more important.

Best regards
    Hartmut



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