[mythtv-users] Mytv Unreliable

[Mike Dent]

On 26/03/2008, Mike Perkins <mikep at randomtraveller.org.uk> wrote:
>
> James Cummings wrote:
> > On Tue, Mar 25, 2008 at 11:05 PM, Tim Sawyer <mythtv at calidris.co.uk>
> wrote:
> >>  I haven't done a channel scan for ages, yet this problem has been
> intermittent
> >>  for ages, seemingly on only one of the two tuners.
> >
> > Given that your address is in the UK (where I am as well), I would
> > strongly recommend doing a rescan of existing transports on a regular
> > basis.  The small variations in channel line-ups and frequencies
> > *always* cause problems on my box (with a Nova-T 500).  It will be
> > recording fine for awhile, then suddenly not be able to find files for
> > programs it believes it has recorded.  A rescan of existing transports
> > always seems to solve this.  Whenever another freeview STB of mine
> > announces that "There has been a change in channel line-up" (even if
> > it doesn't turn out to be a visible), I always go into the lounge and
> > rescan the mythtv box.  This seems to happen every few weeks.  This
> > seems to solve the problem.  Perhaps it isn't the rescan of existing
> > transports, but the stopping and restarting of the backend that one
> > has to do to run the setup... but that is what seems to work for me.
> >
> > I'm going to be upgrading the box from Ubuntu feisty to gutsy soon
> > (in preparation to eventually upgrade to Hardy in a couple months or
> > so)... I hope that doesn't mess things up too much.
> >
>
> You can get some indication of channel changes by checking the backend
> log(s) on
> an occasional basis. I can't remember the exact message to look for, but
> if your
> logs suddenly start growing rapidly (you do use logrotate, don't you?)
> then it's
> worth a check, and then a rescan if necessary.
>
> Another fun thing to watch out for is if your aerial is able to pick up
> from
> more than one transmitter. As the transmitters (people) are in the process
> of
> changing the transmitter (equipment) power levels you may find that
> channels
> which were in one multiplex suddenly move to another one and thus
> disappear from
> your lineup.



Well, this is what caused me some problems just recently. I'd upgraded last
week from Ubuntu 6.10 to 7.10 and with it to MythTV 0.21. I ran mythtv-setup
and deleted my tuners as recommended and then did a rescan of channels,
in the past before the upgrade this has seemed to work ok.

However I noticed that the quality of picture after the scan seemed much
worse than with ubuntu 6.10 and mythtv 0.20.2?
There were many more pops/squeeks and digital signal drop outs than before,
I had not physically moved the PC
whilst doing the upgrade (combined be/fe) but I started checking all the
connections to the aerial, even re-made some of them. Checked the pre-amp
etc etc. Still no improvement.

I'd kind of given up on it and then yesterday morning I put it on just to
see if anything had improved and was greeted with a 'no signal' message
across all channels! I rebooted just in case and it was the same, I switched
the TV off in disgust.

Later that day I heard that our local TV transmitter, which is about 7 miles
away was off air for maintenance, *all day*.
It did not concern me as I was pointing at a more distant transmitter which
in my location (surrounded by taller buildings in some directions) gives a
better signal. Then the penny dropped. Could it be that my MythTV box was
tuned in to the wrong transmitter all this time and when I checked it this
morning and there was no signal, that was the local transmitter off air!?

I confirmed with some family that the local transmitter was still off and
decided now was an ideal opportunity to do a re-scan for channels! I did
this and what do you know, the signal quality is much better and just like
it used to be.

As I am in the UK too, I will be checking the websites below and making sure
this does not happen again.

Mike




This link gives you the exact frequencies for each UK TV channel:
> http://www.digitalspy.co.uk/terrestrial/tuning/
> note that the DVB multiplexes use centre frequencies; the ones given above
> (I
> believe) are the lowest frequency in each channel band. Then use this
> link:
> http://www.dtg.org.uk/retailer/transmitters.html
> to find out which transmitters near you use which channels to send which
> multiplex. Use the Transport Editor screen in mythtv-setup to find out
> which
> multiplexes the full scan picked up, and work out which transmitters sent
> which.
> Delete ('D' key) the ones you don't want, then 'Rescan existing
> transports' to
> give you a clean channel line-up. This Link:
> http://www.dtg.org.uk/retailer/dtt_channels.html
> will tell you what digital channels are carried by which multiplex. * This
> list
> is the one which can (and does) change from month to month.
>
> Incidentally, I use three K-World DVB-T 100 cards (£30 each from Maplin)
> to get
> my digital input, and have found no difference between the cards. They do
> take
> 25-30 watts *each* power, so should only be used in a well-ventilated back
> end.
>
> Hope this helps.
>
>
> Mike Perkins
>
>
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