[linux-dvb] ves1820 qam256 - tt dvb-c 2.1
roh at hyte.de
Sun May 7 01:45:31 CEST 2006
On Fri, May 05, 2006 at 12:08:37PM +0200, Marco Skambraks wrote:
> I have the same problem like Halim Sahin with his tt dvb-c 2.1
> the card works fine with qam64 channels
> channels with higher modulation like qam256 produce several dropouts
> I already tried to change the PWM in ves1820.c - with no effect
> according the ves1820 spec the frontend should support qam256
> so, it looks like a linux driver problem
have you tested that your cable is working properly?
qam64 has a much less bits_per_mhz_and_timeslot value and thus is less
prone to have problems if the cablesignal is not perfect.
in the real world that means: check with a box known to be supporting
if it doesn't work you'll need someone with a measuring-reciever which
can display a constellation-diagram. (meaning you have a matrix with I
and Q as rulers and if the signal is good a 8x8 dot graphic for qam64
signals and a 16*16 matrix for qam256)
in qam64 the dots have much less space between the dots, and thus a
phase error like from a not perfectly working amp or a tap has much
greater impact (phase errors move the dots circular around the center of
the diagram) on qam256 than on qam64. you can even have perfect qam64
reception and no usable sync on qam256 in that case.
> any ideas how to fix it?
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