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

["Robert Schlabbach" <robert_s@gmx.net>]

From: "Andrew de Quincey" <adq_dvb@lidskialf.net>
> I've been seeing corruption on seemingly random channels when using
> these cards with a satellite distribution system (but not when
> directly connected to a dish).

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.

> 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...

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...

> 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...

Regards,
--
Robert Schlabbach
e-mail: robert_s@gmx.net
Berlin, Germany



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