[linux-dvb] KNC1 SNR goes/went bad

Manu Abraham abraham.manu at gmail.com
Mon Aug 13 22:31:50 CEST 2007


On 8/14/07, P. van Gaans <w3ird_n3rd at gmx.net> wrote:
> On 08/13/2007 09:55 PM, Manu Abraham wrote:
> >>> Can you describe the problem that you face ? other than low SNR ? ie
> >>> have you checked whether your cables are okay, Dish is aligned proper
> >>> etc etc ? It will help to avoid a lot of frustration later. :)
> >>>
> >>>
> >>> Manu
> >>>
> >> That's great!
> >>
> >> The problems I face: I have a lot of BER, measured with femon -h (with
> >> my patch applied for decimal readings). The sky is clear. Visiosat Bisat
> >> G3C dish.
> >>
> >> On ZDF on Astra 19,2 east (Astra 1), I see nothing (and I mean
> >> _nothing_) but green and purple blocks and loud aliens in my speakers
> >> constantly. BER is into 65000.
> >>
> >> On Omroep Brabant on Astra 1D at 23,5 east, I see some bits from the
> >> image but constantly lots of complete stripes with corrupted MPEG, and
> >> the audio is also bad. So this stream is also corrupt. BER into 65000.
> >>
> >> Now ZDF is one of the weakest transponders on 19,2 east and Astra 1D is
> >> old so doesn't perform optimal either. But this is not normal.
> >>
> >> On BBC One/Two/Three/Four on Astra 2D, and that beam is strong in my
> >> location, the picture is good most of the time, but once approx every
> >> minute a small visible corruption passes by. Just as long as it does
> >> _not_ start to rain, I can follow the program. BER into 65000.
> >
> >
> > I understood your problem.
> >
> >> On the Dutch channels on Astra 1 at 19,2 east again, like Nederland 1 at
> >> 12515.25 H (Astra 1G) or RTL 5 at 12343.50 H (Astra 1H) the picture is
> >> perfect, and BER hoovers and shows 0, 256 or 512 (which is low).
> >>
> >> There are also values in between. n-tv on Astra 1 at 19,2 east shows
> >> around 17000-18000. Perfect picture.
> >>
> >> But.. When it starts to rain, the whole party is over.
> >
> >
> > During rain, don't expect anything much with DVB-S
>
> With just a little normal rain, DVB-S should work fine. Only when
> there's hard rain and it's seriously cloudy you could expect the picture
> to actually fail with a properly set up dish. Overall DVB-S is very
> reliable. DVB-S is also used as a feed for many cable channels in The
> Netherlands, and they hardly ever fail.
>


By rain i meant, by the rain we have here, we don't receive any DVB-S.
Don't know how many cms of rain ..


> >> So that's my problem. When I swap the KNC1 for my Technotrend S-1500,
> >> all the channels work, including ZDF, perfectly, and the BER is zero
> >> everywhere, even ZDF works with zero BER. There are many other channels
> >> that do not work but I couldn't possibly list them all, I don't think
> >> that would make sense anyway. And sure, there could be a little
> >> difference in tuner quality and stuff in favor of the Technotrend, but I
> >> really don't believe it would be that big for cards from the same price
> >> range. And it's not like Philips is a bad or cheap brand either.
> >
> >
> > Though i am not saying it is bad, devices designed improperly leads to
> > bad results. However good the components are. We have examples, but
> > not stating that is the case here, but a possibility.
>
> Yes, that's true.
>
> >
> >
> >> I'm actually not sure the SNR number in femon is low, I was really
> >> talking about Signal to Noise ratio - with all that corruption and
> >> horrible performance it has to be bad.
> >>
> >> On Windows, I can watch ZDF with the KNC1, but I see some "error" level
> >> in the  Windows software, that "error" most likely means BER. But it's
> >> not much. Last time I checked anyway, it's been a while since I've seen
> >> Windows.
> >
> >
> > If this is an overall problem that you see, then it has nothing to do
> > with the drivers. I thought in your case, the driver was misbehaving
>
> It's not an overall problem, I only have this problem with the KNC1 card.


Maybe it is a hardware specific problem, 2 options again

* The card type as a whole is bad
* The specific mentioned card has a hardware problem.


> >
> > The TT card you have behaves similarly ?
>
> The TT card performs fine, I still have to test it in somewhat harder
> rain, but the fact it shows ZDF perfectly without even BER is a huge
> difference.
>
> I also have a Vantage standalone receiver. I did test that one in rain,
> and ZDF would just keep going.
>


Ok, so your dish/LNB setup is fine, then.


> >
> >> The problem seems to be getting worse, because some days/weeks ago I
> >> believe I had zero BER at the Dutch channels, and now it's around
> >> 256-512. But the weather, temperature and other stuff also varies, so
> >> it's always hard to say.
> >
> >
> > Maybe it has something to do with your dish alignment, LNB alignment
> > etc ? A LNB skew can cause a lot of errors to happen, eventhough the
> > dish is aligned correctly.
> >
>
> Trust me, I know stuff about alignment. I have re-aligned the dish 5 or
> 6 or more times and _every_ time the result did not fully satisfy me. I
> changed the height of the dish, how deep the LNB was into the holder,
> the skew, tried moving the LNB holder up and down (possible on my dish),
> I tried everything. Even swapped the LNB's, but that made no difference
> either. The last couple of times, I took my laptop up on the roof so I
> could VNC to my desktop and see the signal/BER instead of using the
> cheap satbeeper. Then I swapped the card for the Technotrend, and
> checked the status... Heeeeey... No signal trouble?


Ok. Cool down


> But OK.. The Common Interface on the S-1500 is totally not detected,
> dmesg never heard of it, it's really like it isn't there, and it's
> required for the Dutch channels. So my choice at this moment is a good
> signal but no Dutch channels, or a crappy signal and Dutch channels.
>
> So what do you do then..
>

Ok, finally back to square one S-1500 issues. I don't have a clue yet
on this, i saw some long long threads, but that's it. I think some
people had success with the patches floating around, but seems you had
bad luck with that as well.

Aargh!



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