[linux-dvb] Re: 13/18V voltage with DVB-S 1.6 (Grundig 29504-491)

[Johannes Stezenbach <js@convergence.de>]

On Tue, Jun 01, 2004 at 12:02:09PM +0200, Dr. Werner Fink wrote:
> On Tue, Jun 01, 2004 at 10:55:24AM +0200, Johannes Stezenbach wrote:
> > Dr. Werner Fink wrote:
> > > 
> > >      this card in the subject does have sometimes problems
> > > with horizontal transponder, especially with the that of
> > > ZDF and KiKa.  It seems that the voltage may be to less
> > > (< 18V).  If I use a so called inline amplifier the no
> > > of the horizontal transponders are visible whereas the
> > > vertical are really perfect and very fast switched.
> > 
> > What good can such an inline amplifier do? It will only add noise.
> > I don't know much about the Grundig FE, but probably you
> > should check your cables and LNB?
> 
> Already done: All F connectors are clean and dry. The cable
> is high shielded one and a so caled 100dB coax.  Beside this
> there are no shorts between the shield and the conductor.
> The LNB works perfectly with a normal receiver. Only the
> window cross cable reduce the signal strengh about 3dB
> and slightly increase the noise.  This was the reason for
> me to give the inline amplifier a try directly behind the
> LNB out connector ... and it really increase signal strengh
> and the noise is not measurable changed ... but only on the
> vertical transponders.  The horizontal are simply lost with
> this amplifier. I guess that the power for the amplifier
> (got from the receiver in this case from the DVB card)
> reduce the power for the LNB and it drops under the
> required switching voltage.
> 
> Without amplifier it depends on the weather ... if the
> weather is fine, the signal of the ZDF transponder
> (11954 MHz horizontal on Astra S19.2E) is good enough but
> with some rain or heavy clouds the signal is worse short
> after switching on to this transponder, some seconds after
> switching on the signal gets better.  Heavy rain kills
> the signal on this transponder, and other horizontal go
> also worse but stay mostly visible.

So does the amplifier actually improve anything with the
normal receiver? I doubt it. If your dish is too small
or misaligned, no amplifier can compensate for that.
A strong signal results in a high signal-to-noise ratio, but
an amplifier will amplify bot signal and noise, and add some
additional noise, thereby making mattters worse. It's better
to invest your money into a better dish and/or LNB.

It may well be that the NIM in your normal receiver is
of better quality than the one on your PCI card. It's also
possible that our driver isn't as good as it should be.

Johannes