[mythtv-users] Too many multiplexes (UK)
mikep at randomtraveller.org.uk
Fri Sep 28 11:46:07 UTC 2007
Recently I had to replace my aerial array because it had become dangerous.
The new setup is so much better that it's now causing me problems with scanning
that some small adjustments to the code may be of help to others besides myself.
I am situated about 8-10 miles from Hannington. My aerial points to about 150
degrees or so (30 deg. east of south). When I do a scan I get all the
Hannington channels, as expected, but also some from Crystal Palace (90 deg) and
some labelled Oxford/Bexley (0 deg/100 deg) (!). As all these multiplexes
contain the same digital channels it makes a right mess of the channel table.
The channel numbering in particluar can be completely randomised every time I do
a rescan (thanks MTD!) depending on the weather and atmospheric conditions at
When I do the scan, the display is completely blocked by a dialog which shows
virtually nothing except a progress bar and various field labels. The only other
variable shown is "Offset 2". Behind it, I can see the listbox scrolling up with
potentially useful information, but I can only look at this when the scan ends.
(1) One of the items shown in the listbox, when a multiplex is found, is the
source, hence "Hannington", "Crystal Palace" and "Oxford/Bexley". It would be
extremely useful if this item was added as a new column in the dtv_multiplex
table and displayed in the Transport Editor dialog. It would also be useful if
an "ORDER BY frequency" clause were added to the Transport Editor listbox
display. At the moment the items are displayed in a seemingly random order and
it is difficult to separate the wheat from the chaff.
It is possible that the behaviour above is UK-specific and would not be useful
in other parts of the world.
(2) The scanning dialog box seems to serve no useful purpose. The information
shown could just as easily be displayed as fields below the results listbox.
(3) It might be possible to do a pre-scan, just identifying the multiplexes, and
then to ask the user to choose which ones they require before processing the
digital channels within.
I'm using http://www.dtg.org.uk/retailer/transmitters.html and I also found this
http://www.digitalspy.co.uk/terrestrial/tuning/ to be very useful. I am supposed
to pick up digital muxes on channels 40, 41, 43, 44, 46 and 50 from Hannington.
I can also receive 22, 25, 34, 48, 52 and 68. The analog channels are a similar
 The old array had a 2.5m (8 foot) pole with two band IV/V aerials
sandwiching a Band II FM aerial pointing in a different direction. The whole
thing was attached by a bracket mounted on the bargeboard at the side of the
house. It swayed alarmingly in high winds. The birds loved it. When we took it
down we got a bucket and a half of water from inside the tubing. The feed cables
were loosely draped over the roof and down the walls.
The new aerial is a wideband digital-quality item. The aerial downfeed is
high-grade CT100 foam-filled satellite cable. The bracket supporting the two
metre down tube is bolted to the brickwork at the side of the house, so it's
unlikely to move. The cable goes straight into the loft space and runs to the
opposite side of the house, straight into the top of my computer cupboard, about
15 metres/50 feet.
When the aerial guy tested the signal after installing, he found there still
wasn't quite enough signal at the top end of the range (where analog channel 4
is). He added a masthead amp, but rather than putting it up the pole, it's
mounted on the inside of the wall where the cable comes through.
The power supply for the unit is in the computer cupboard. I have a 4-way splitter
three of which outputs go to my DVB-T cards in the master backend. I also have a
which I am using as a combiner, the inputs being the fourth output from above
and a feed from my NTL set-top box, which is currently downstairs. From there
the output goes to a distribution amp which sends the signal to sockets all over
 Although I am quite close to the transmitter, as the wood-pigeon flies, I am
on the wrong side of a hill and there is a band of mature trees not 10 metres/30
feet from the aerial. This means the signal strength goes from quite good in the
winter to average in the summer. (At the end of the garden I have the A339 in a
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