[mythtv] [mythtv-commits] Ticket #1485: DVB Scanning Issues
stuarta at squashedfrog.net
Fri Mar 24 10:59:08 UTC 2006
On Fri, Mar 24, 2006 at 09:50:27AM -0000, MythTV wrote:
> #1485: DVB Scanning Issues
> If I understand you correctly "Eventual goal would be to pick the best
> frequency (signal/quality) and use that in the database" - you may not
> have considered how these frequencies are used for dvb-t in the UK.
> Presumably in order to prevent interference from different transmitters -
> each transmitter uses the centre frequency OR a single frequency selected
> from this list - if the other_frequency flag is set then the centre
> frequency is not used on that transmitter and one of the frequency list is
> used. The only case where two frequencies would be transmitting the same
> transport is in regions that were in range of two transmitters.
This disagrees with practical observation.
I'm on Crystal Palace and all of my mplexes have the other freq flag set
with 3 alternate frequencies each, but the signal is transmitted on the
> The issue that makes scanning a pain is that the frequency list and main
> frequencies for each transport may overlap - so you could test the signal
> on that frequency and get a valid strong signal - but it would actually be
> for a different transport - so selecting the strongest signals could
> actually lose you a transport.
This will make scanning for transports more challenging but still very
doable. It just means if we check the alternate freq for a transport and
the tsid is wrong, then clearly that isn't in use for this transmitter.
We would just need to walk the freq list, starting from the centre freq
and then moving onto the alternate frequencies listed in the NIT.
> I tried to explain this (very longwindedly) in #841 - I haven't tried to
> update that because I was waiting to understand the design of the new
> signal monitoring daniel was planning for .20
> - good luck!
Could you privately send me a copy of your nit table generated from
dvbsnoop -n 1 -nph 0x10
and a list of your actual transmit freqs of your muxes from the db.
select mplexid, transportid as tsid, frequency from dtv_multiplex;
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