[linux-dvb] Re: My DVB-c patch (Re: The drivers and HTV)

[Holger Waechtler <holger@convergence.de>]

Ralph Metzler wrote:
> Holger Waechtler writes:
>  > Dennis Noordsij wrote:
>  > >>- Disables zigzag for everything except DVB-s.  This is from Metzler
>  > >>  driver.  Maybe someone with DVB-t needs it?  In that case change the
>  > >>  "!= FE_QPSK" to "== FE_QAM".
>
> Sorry, I only disabled it for debugging a new cable frontend which was
> impossible with zigzag turned on.
>  
>  > > Disabled zigzag. For QAM_64, if I hit the exact frequency, it locks 
>  > > immediately. Picture is perfect, etc. But I have 2 cards, and if I let the 
>  > > frequency bending step in (i.e. offset the frequency by one stepsize, 
>  > > 62.5kHz) locking for that card becomes more unreliable, it does better if it 
>  > > doesn't bend the frequency at all. So it's very touchy, if I step 62.5kHz 
>  > > away from the "right" frequency the results get much worse.
>  > 
>  > Ok, I'll postpone applying this patch. You can't simply disable 
>  > frequency bending when you have multiple cards in the same box. When 
>  > both try to tune on the same frequency I had in some setups the effect 
>  > that both frontends loose lock due to RF interferences.
>
>
> Does this really happen with multiple cards or only if two tuners are
> on the same card/board right next to each other?
The strongest effect you can see when 2 poorly shielded frontends are 
connected directly side by side. But if the GND routing is not optimal 
this happens even when the frontends are placed wider away.

The good thing about PCI cards is that they usually have a solid GND 
plane in the PCB between the 2 tuners, but for STBs this is rarely the 
case...


>  > >>- Has anyone ever tested this auto inversion thing?  DVB-c is far too slow
>  > >>  to tune and lock for this auto inversion code to work.  Therefore you
>  > >>  need to manually set it.
>  > > 
>  > > 
>  > > I had inversion turned off with the reg0 |= 0x20 code in ves1820.c
>  > > (Your HTV channels.conf specifies inversion off for all channels, hope that 
>  > > was right :)
>  > 
>  > You should use INVERSION_AUTO if you don't know for sure your providers 
>  > inversion settings.
>
>
> But it should also be possible to set it manually.
This is only possible if you know how Tuner and frontend are connected. 
For the ves1820 are both versions out there, as well for the stv0299 
based frontends. Some verndors simple swapped I and Q pins, so the 
spectrum is virtually mirrored.

Holger



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