[mythtv-users] Digital switchover in UK: duplicate channels

John Pilkington J.Pilk at tesco.net
Wed Aug 17 16:25:51 UTC 2011

On 17/08/11 15:16, Simon Hobson wrote:
> John Pilkington wrote:
>> I retuned today as the last-but-one stage of switchover at Waltham, East
>> Midlands.  All went smoothly but I wasn't able to stop it listing two
>> different channel numbers for BBC FOUR, CBeebies, BBC Parliament and the
>> BBC Radio channels.  It appears that at present these really are
>> duplicates; they are available on two muxes.
> This is common where you get a signal from more than one transmitter.
> There were a lot of complaints around (IIRC) the Chester area at
> switchover as they started getting Welsh variants of BBC2 and C4. In
> this case they were getting signals from two main transmitters, but
> it also happens if you get signals from the main transmitter and a
> repeater.
> In these cases, the system fills in channel numbers as it finds
> muxes. Up here (Winter Hill area) our main transmissions are from up
> the top end - so all the repeaters come further down. At a mates
> house, it picks up the barely usable (the aerial points the other
> way, so very low signal strength) local transmissions first and puts
> them in the main channel slots. Then when the unit finds the main
> muxes, it puts the "duplicate" channels up at 800+. For naff boxes
> with a dire excuse for a user interface, this sucks big time.
> Fortunately for us, because of the way the muxes are laid out, I can
> unplug the aerial lead until the scan has passed the local
> transmissions, and avoid the problem.
> In MythTV, I can see a number of ways round the problem.
> 1) Delete all channels and delete all transports.
> Perform a tuned scan on one frequency at a time - there's only 6
> muxes to pick up.
> 2) As above, but experiment, and see if the option to find related
> transports will pick up just the muxes from the same transmitter.
> Then rescan existing transports.
> 3) Manually delete the transports you don't want, delete all channels
> and do a scan on existing transports.
Yes: I did various mixes of 2 and 3.  I don't think I have a problem 
now, but it's clear that all six transports that I now see are coming 
from _the same_ transmitter.  I suppose that this is a temporary fix. 
All the netids are the same.  It looks as if four of the muxes are 
linked and populated if I start with one the frequencies I listed (642 
MHz), but if I start with the first-listed (794 MHz) I get all six.

My post quoted the frequencies found.


John P

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