Kari Salmela wrote:
I have had similar experience like You with the same card (TT DVB
C1500)
regarding QAM64. I discovered that there had been a successful fix for
this done for QAM128 by changing the sweeprate, see
http://www.linuxtv.org/pipermail/linux-dvb/2006-February/008439.html
So I made some test to find a working sweeprate for QAM64, see
http://www.linuxtv.org/pipermail/linux-dvb/2006-May/010141.html
You might have to the same trip for QAM256?
+ case QAM_256:
+ delay = 200;
+ sweeprate = YOUR_SWEEPRATE;
+ break;
default:
return -EINVAL;
I am experiencing same problem with QAM 256 .. Tried putting sweeprate =
250, but it seemed to make no visible difference. Is there any other way
to figure out what could be right than just trying different values and
recompiling?
I'm sorry, but I didn't do my tests in any other way than what You
describe above. In some of my early tries I also included changes of
delay parameter also, but when I got the result that I wanted I removed
the delay changes to see if I could get a minimal patch. You might have
to include the delay parameter also.
BUT all of this is guessing, I have NO knowledges about the meaning what
this parameters does. The thing that got me thinking that You have the
same problems that I had is that the symptoms is similar to mine.
Maybe one of the dvb gurus out there could help us understand the
underlaying meaning of this parameters and give some tips of good
thumb-rule values?
--Kari
/Per
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
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