[linux-dvb] Re: TT budget DVB-C 1.0 tuning issues

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

From: "Esa Loukkola" <esa@nic.fi>
> 146MHz, symbol rate 6900 and QAM128 and 154/6900/128 do not tune at all;
>
> The common denominator for the two frequencies that don't tune are that
> they are the lowest in my network. 162MHz and all above it tune well
>
> Upon browsing this mailing list, I came upon several alternative magic
> numbers for inittab values and PWM values in ves1820.c.

PWM is meaningless on this card, it only matters on the Siemens DVB-C
cards, where the PWM output is wired to the VCO control of the TDA9819 IF
AGC.

As to your card, this sound like it might be a band switching problem. I'm
not sure if the frontend driver has been programmed according to the ALPS
TDBE2 specs - at least I have _not_ been able to find them anywhere, so
maybe the current code is just "guesswork".

So look at the function tuner_set_tv_freq() in VES1820.C, the ALPS TDBE2 is
tuner_type == 1 and buf[3] is the band selection. I'd suggest inserting an
override like this:

if (tuner_type == 1) {
        buf[2] |= (div >> 10) & 0x60;
        buf[3] = (freq < 174000000 ? 0x88 :
        freq < 470000000 ? 0x84 : 0x81);

/* experimental band switch byte override */
buf[3] = 0x??;

} else {

Now for 0x??, try all possible combinations of the lower nibble, i.e. 0x80
through 0x8F. You could also try different charge pump settings, i.e. 0x0?,
0x4?, 0xC?.

If all of this doesn't work, the next thing would be to try and hunt down
the ALPS TDBE2 data sheet, maybe it has some information on proper band
selection...

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



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