[mythtv] Current DVB problems rundown

Daniel Kristjansson danielk at cuymedia.net
Sun Sep 11 05:38:08 UTC 2005

On Sun, 2005-09-11 at 04:04 +0200, Kenneth Aafl°y wrote:
> > I don't like this, it violates the principle of least surprise.
> > Normal everyday actions such as changing channels and making
> > recordings should not mess with the transponder/multiplex table.
> It should not modify the original value in the database, but either enter it 
> into a separate field or as a list in the frequency field.
That might work.

> > This capability is already present in DVBSignalMonitor... You just
> > have to add the kDTVSigMon_WaitForMGT or kDTVSigMon_WaitForNIT flag,
> > for ATSC or DVB, resp.
> Hu, the NIT can take a huge time to get, why not SDT as that's transmitted 
> more frequently, or event the PAT?
Well actually it uses the PAT right now for DVB channels, and a VCT 
for ATSC channels. I thought you wanted to verify the NIT.
(It caches the VCT pids from previous tunes, but also waits for
MGTs in case the VCT pids are out of date.)

> > I don't expect this to swing widely very often.

> Hmm, wonder if that reasoning applies here:
> - My LNB sits on the sunny wall, like everyone elses, which would easily
>   cause a very large temperature difference. Not to mention summer and winter.
> - The LNB converts the frequency of the signal down about 1Ghz.
I didn't think of this; an LNB sitting in the sun, even in a 
white ventilated PVC case will experience huge temperature swings.

Maybe caching some dated frequency values is worth the effort. Can
you chart the drift on a transport over a 24hr period, once per hour
say? If the drift is is like 100 kHz it's not worth the effort, but
if it is closer to 500 kHz it is.

-- Daniel

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