Some Freeview channels breaking up

  Pineman100 19:11 12 Oct 10
Locked

Over the past couple of nights, I've had several Freeview channels giving trouble. They're fine for the first few minutes of watching, but then the picture and sound both start to break up. This happens progressively - break up, recovery, worse break up... and so on, until everything disappears and the screen simply shows a "No Signal" sign.

This has happened on Dave, BBC4 and several other channels (maybe a third of the Freeview channels). The remaining channels are fine.

The problem has happened on two TV sets, each with its own Freeview box.

Has anyone else experienced this? Any suggestions what might be wrong, please?

Are you using a rooftop antenna?

Had another thought, some channels are Grouped to use the same multiplex (may not be correct terminology) but if some are fine and some are not that could be the reason - poor reception of that particular multiplex.

  mooly 19:31 12 Oct 10

See if you can find in the set up menus a signal quality readout and also what "multiplex" each problem channel is on.

Make a note of the problem channels... are they all on the same "multiplex" ? There are normally 6 multiplexes which carry all the channels. Sometimes receivers lock onto an incorrect channel from a relay or another area even.
Google your regional transmitter.

This was/is a problem on Winter Hill for example'
click here

When regions changed to digital some made use of a different part of the band... and old aerials were historically "channel grouped" to work well in a narrow part of the band, so if that happened in your area it's something to consider.

  Pineman100 19:47 12 Oct 10

I think I'm operating above my pay-grade here!

To answer your various questions as best I can:-

Yes, we have a digital rooftop antenna. Its signal is shared between the two Freeview boxes, and until a couple of nights ago, was working fine.

I'm afraid I have no idea about which channels share which multiplex. How would I find this out? I've never seen any mention of this on either of the Freeview boxes.

Our transmitter is Tacolneston in Norfolk. Here's a report I've just read on the UK Free.TV website:

"TACOLNESTON transmitter - Over the next week Tacolneston main transmitter: TV (analogue) working normally, TV (digital) working normally, Radio (analogue) Possible weak signal, Radio (digital) Liable to interruption. "

This suggests that some work is going on, although it says that digital TV is OK - do you think this could be responsible?

  woodchip 19:55 12 Oct 10

Firstly, there is no such thing as a digital antenna. As to your antenna I suggest you check all connections from it to the TV Also Cable may be kaput if its a old cable

  woodchip 19:57 12 Oct 10

Firstly, there is no such thing as a digital antenna. As to your antenna I suggest you check all connections from it to the TV Also Cable may be kaput if its a old cable

PS digital is created by electronics not lumps of Plastic and aluminium

  lotvic 21:03 12 Oct 10

It's the Inversion Effect of the weather, High pressure reflecting signals and interfering with each other.
(sounds real techie :) click here )

  Pineman100 22:55 12 Oct 10

Woodchip - the aerial man said it was a digital antenna. I suspect he knew he was dealing with an ignoramus! I assumed it was an aerial specifically designed for receiving a digital signal.

However, it is a pretty new one (only about 2 years old) with new coax cabling. The splitter is only about 1 year old, and has the latest type of screw-in connectors.

Lotvic - I read the page that you linked to and I'm confused. It says:

"The digital television signal uses a format called COFDM (coded orthogonal frequency division multiplexing) and this incorporates the ability to ignore reflected digital signals.

However, analogue television signals do not co-operate with each other and the picture quality is reduced."

This seems to suggest that the Inversion Effect may be deleterious to the analogue signal, but not the digital. Or have I misunderstood?

  esbe 23:53 12 Oct 10

Mine is the same here in Suffolk,it might be due to the current high pressure weather.

click here

cheers.

  lotvic 00:27 13 Oct 10

This is the bit that I meant
"The very weak digital signals that are a(sic) used (until digital switchover) for Freeview can be badly effected by interference from reflected signals from adjacent analogue transmissions."

So that means the digital signals are being interfered with by the analogue transmissions because of the weather.

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