[linux-dvb] Re: CX22702 conexant/leadtek support

[Holger Waechtler <holger@qanu.de>]

Andrew de Quincey wrote:

> On Tuesday 07 Sep 2004 12:18, John Dalgliesh wrote:
>  
> > On Tue, 7 Sep 2004, Andrew de Quincey wrote:
> >    
> > > On Tuesday 07 Sep 2004 11:16, John Dalgliesh wrote:
> > >      
> > > > On Mon, 6 Sep 2004, Andrew de Quincey wrote:
> > > >        
> > > > > Now that the cx22702 code is there, I've added support for the tuner
> > > > > on the Conexant reference design (Thomson DTT7579) - this is what the
> > > > > Leadtek LR6650 card appears to be as well.
> > > > >
> > > > > I do not have one of these cards - the tuner code is based on my
> > > > > initial analysis for the new Nova-t before I heard about Steve's
> > > > > driver. I cannot confirm it works correctly as it has a different
> > > > > tuner. It should do though. The cx22702 code _may_ need some
> > > > > additional tweaks if the reference design is wired slightly
> > > > > differently.
> > > > >          
> > > > I can confirm that the tuner config is correct for the DTT757Xs that
> > > > are used on DVICO's FusionHDTV DVB-T Lite .... not that that is
> > > > probably any help to you since you are concerned with a completely
> > > > different board :D
> > > >        
> > > Are those at all based on the conexant reference design out of interest?
> > >      
> > Not sure, but if so then they didn't think very much of it - it's got a
> > Zarlink MT352 demod and a (cheaper? older?) Fusion 878A as the PCI bridge.
> >
> > So no, probably not ;)
> >    
> Aha - one question, am I right about it not having a SAW (7/8MHz switchable 
> bandwidth) filter? Robert pointed out that maybe the driver I was looking at 
> just hadn't written that piece of code - I've got no way of knowing.
>  
Modern Direct-Conversion tuners don't necessairily need an SAW filter 
anymore, they can filter using cheap L/C or R/C filters combined with 
digital IIR/FIR filters in the demod. See e.g. 
http://www.highfrequencyelectronics.com/Archives/Jun04/HFE0604_DirectConv.pdf 
for some theory, you'll find may more references on the web.

For 6/7/8MHz DVB-T signal the center frequency of the downconverted 
"zero-IF" input signal is usually around 4...4.5MHz, the lowpass cut-off 
frequency around 8...9MHz.

Holger