[linux-dvb] KNC1 SNR goes/went bad

P. van Gaans w3ird_n3rd at gmx.net
Mon Aug 13 22:18:38 CEST 2007

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.

>> 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.

> 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 

I also have a Vantage standalone receiver. I did test that one in rain, 
and ZDF would just keep going.

>> 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?

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..

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