[linux-dvb] KNC1 SNR goes/went bad

P. van Gaans w3ird_n3rd at gmx.net
Tue Aug 14 22:40:12 CEST 2007

On 08/13/2007 10:31 PM, Manu Abraham wrote:
> 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 ..

I don't know where you live. In The Netherlands, with a 64cm dish (which 
I have), only in heavy storm the signal isn't strong enough. Occasional 
rain is no problem here.

>>>> 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.

Both are possibilities, I have no idea.

>>> 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

Sorry, I've been pretty frustrated with the dish myself. It's hard to 
get on the roof here (usually have to wait a couple of weeks every time 
for dry weather that lasts so the roof isn't slippery wet anymore), and 
every time the KNC1 gave a bad signal I got back up on the roof and 
tried to align it better. Now that I've figured out the KNC1 will maybe 
never give a good signal, at least not with the current drivers if 
that's the problem, I'm a bit frustrated.. All that time on the roof was 
wasted. So yes I'm a bit frustrated about that, I shouldn't project it 
on you..

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