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

Petri Helin phelin at googlemail.com
Thu Apr 12 15:03:24 CEST 2007


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.


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