[linux-dvb] Pinnacle PCTV Sat HDTV Pro USB (452e) packet loss
linuxdvb at johngoacher.co.uk
Sun Dec 16 21:35:53 CET 2007
Daniel Golle wrote:
>i also noticed glitches on some channels, but not all.
> Using szap2 (or the patched version of VDR 1.5) on Astra 19.2E
> works perfect and didn't show a single error in several hours of
> recording, while
> rarely gives any complete picture at all - usually vdr-softdevice
> crashes after some seconds...
> this pointed me to a possible dependency on the symbol rate, but i
> didn't investigate it further. as I'm currently waiting for a new LNC to
> be delivered, i cannot run any meaningful test at this moment (but
> hopefully next week).
I've now carried out some additional tests to try and pin down which
parameters affect the results. I tried the following 6 channels on Astra
Rhein main TV:12633:h:0:22000:208:308:12614
The first three channels have symbol rate 27500, the second three have
symbol rate 22000.
I captured one minute of data from each channel and then ran the files
through TSReader to check for errors. The data from the channels with symbol
rate 27500 is perfect. However, the data from all the channels with symbol
rate 22000 show errors, typically in the range 300 to 500 continuity errors
in a one minute period, which works out at around 1 in 300 packets lost on
This seemed to indicate the problem is linked to symbol rate, as you
suggested. However, I then repeated the test on Astra 28.2E, which has a
stronger signal at my location. I tested a couple of channels which have a
symbol rate of 27500, for example Sky News. Both of these showed continuity
errors. Therefore the problem cannot just be linked to symbol rate.
I then performed a full scan of Astra 19.2E and 28.2E using DVBViewer under
Windows. This scan indicated that all the above channels on 19.2E which have
symbol rate 27500 and show zero data loss have a FEC parameter value of 3/4,
whereas the channels on 19.2E which have symbol rate 22000 and show data
loss have FEC 5/6. On Astra 28.2E, the channels with symbol rate 27500
(e.g. Sky News), which show data loss have FEC 2/3.
This leads me to wonder whether the dependency is in fact FEC related, as
only FEC 3/4 gives an error free stream in the above tests. If I could find
an error-free channel with symbol rate 22000 and FEC 3/4 this would
eliminate symbol rate as an issue. However, there do not appear to be any
channels on 19.2E or 28.2E configured in that way.
Of course, there are other devices out there which also use the STB0899
module. Could anyone who is familiar with this module shed any light on the
issue ? I should emphasise that all the above channels are error-free under
Windows on the same hardware with the same feed, so the problem doesn't
appear to be related to signal quality.
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