[linux-dvb] Re: DVB-C QAM128 errors and signal strength

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

From: "Jarkko Lavinen" <jlavi@iki.fi>
> I bought 2 Siemens DVB-C cards with analog module from Dvbshop

The frontend on these cards consists of CD1516L tuner, TDA9819T IF
Amplifier and VES1820 demodulator.

> I don't understand why the signal strength is stuck at maximum.
> It shows different values when there is no signal and cable is
> removed from the card.

The signal strength reads the VAGC register, which I think has no meaning,
as the AGC of the VES1820 is not used, and the TDA9819T determines the
signal level. In other words: You cannot read the signal strength on these
cards.

> To me this looks the signal is saturated and perhaps too strong,
> and overdrives the tuner and the frontend.  Could the errors be
> caused more by distortion than by noise?

Try reading the saturation registers of the VES1820 (0x21 through 0x27) to
find out...

> Has anybody had similar problem and tried signal attenuator?

Before you do that, you should really dig into the VES1820 a little and toy
with its register settings, maybe it is just not properly configured. Make
sure that the symbol rate is correctly calculated and that the frequency is
correctly tuned (read register VAFC) and make sure the correct values for
128-QAM are written to registers AGCREF, MSETH and AREF.

I would try that myself, but I don't have any 128-QAM signals in my
cable...

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



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