[linux-dvb] High number of uncorrected blocks with TT-C1500 and QAM256

Petri Helin phelin at googlemail.com
Tue May 1 16:41:08 CEST 2007


Petri Helin wrote:
> Hi,
> 
> I am not completely sure if this really is connected to the channel
> using QAM256, but that's what I suspect. I use Technotrend's TT-C1500
> budget card with appropriate common interface and Conax CAM. This
> combination works flawlessly on every channel which uses QAM64 or
> QAM128. Now the Finnish cable company, for which I am subscribed to,
> started broadcasting Canal+ Film HD some three months ago. This has
> worked otherwise quite well, but I get constant disturbances/artifacts
> in the picture. I used to think that it was just because the bit rate
> was five times the normal (17 Mbit/s compared to 3-4 Mbit/s).
> 
> But couple of days ago I noticed that this channel is actually the
> only one I am receiving that uses QAM256. Searching the Internet
> provided me with couple of forum threads/mailing list posts that
> suggested that certain DVB-C cards might have problems in receiving
> QAM256 modulated broadcast, but the hits were mainly on VDRportal and
> in German and I might have lost something in the translation... In
> addition to the picture getting garbled every now and then I can
> notice the problem also from the high values of UNC (uncorrected
> blocks) and BER (bit error rate). On Canal+ Film HD UNC is between 0
> and 20 and BER is about 250. On all other channels UNC is 0 and BER
> close to 0. STR ja SNR are the same on all channels, including Canal+
> Film HD.
> 
> Now what I am asking is for any experiences using DVB-C cards to
> receive QAM256 modulated broadcasts, no matter if HDTV or not.
> 
> -Petri
> 

To give you all an update on this matter, all problems with the picture 
vanished once I removed the common interface and put the subscription 
card to a smartcard reader. So it looks like either the CI ("BDGTCIS Rev 
1.1 TT2004.14") or the CAM (Dual Irdeto & Conax) I used caused the 
artifacts in the picture.

-Petri



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