[linux-dvb] Re: Budget SU1278 (STV0299/TSA50059) DVB-S corruption on SOME channels

[Andrew de Quincey <adq_dvb@lidskialf.net>]

> So have others, apparently - there have been various threads in this
> newsgroup recently (see e.g. the thread "Brandnew Nova-Ci"). It seems to be
> linked to the new TechnoTrend card design (with SU1278/SH[A] frontend) in
> conjunction with multiswitches.

Yep, thats it exactly.

> > Searching on the web led me to a philips document ("su1278.pdf") which
> > describes the optimal settings for the SU1278 on page 10. The driver is
> > not using these right now. I'm experimenting with the recommended ones,
> > and they do seem to help.
>
> FWIW, in my Windows driver, I have changed one STV0299B setting compared to
> the recommended ones: The recommended AGC2 Reference Level (m2) is 0x19,
> but I found that setting it to 0x1F (the maximum) appears to give a better
> SNR...

Ta, I will bear that in mind when I recalculate the AGC related stuff.

> BTW: I also found an issue with low symbol rates: The STV0299B datasheet
> says that the gain CFD[6:4] MUST NOT exceed the coefficient e[3:0], as that
> may lead to instability. But when you take the recommended STV0299B
> settings from the SU1278 datasheet, that is the case for symbol rates <5
> MBaud. Since I do not receive any transponders with such a low symbol rate,
> I have not been able to verify if there is indeed a problem...

I've found all the settings for symbol rate-related calculation in the 
stv0299.c linux driver differ from the recommended values for the SU1278SH. I 
think I'll see if my modifications to the tsa5059 code fix the problem first 
though..

> > Does anyone else have this problem? I don't wanna commit a change to CVS
> > and  break everyone's systems. The changes are to use a step size of
> > 1000kHz (as  opposed to 125kHz),
>
> IMHO it would be preferrable to implement something like in
> sl1935_set_tv_freq(), i.e. selection of the lowest possible divider which
> still fits the target frequency. That's what I have done in my Windows
> driver as well...

Sounds like a good idea, I'll have a look at that code.



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