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Disappearing Channels
Ch. 11. 19,20, 29,37 have all disappeared from our Freeview box. On the TV they are still there but say either No Signal or No Service. Everything else works as it did before. Any thoughts?
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First, a note about retuning:
If your Freeview box asks you to choose between 'adding new channels' or 'replacing channels' (as mine does), you should select the 'replace' option. (You'll probably need to retune after following the advice below).
Now to the cause of your problem. It's simply insufficient signal strength.
Freeview channels are transmitted in 'bundles' (called multiplexes), with each multiplex using a different frequency. In an ideal world your TV aerial should have elements which are exactly the right length to 'resonate' with the incoming frequency. So, theoretically, you need a separate aerial for each multiplex. That's clearly impractical, so you use a single aerial which is only a 'rough match' to each of the frequencies (and is likely to be better at receiving some multiplexes than others). Your aerial resonates poorly with the frequency of the multiplex that bundles the missing channels together.
Further, the signal strengths at your aerial don't remain constant. They're affected by the 11-year sunspot cycle, individual solar flares, atmospheric pressure (and precipitation) and all sorts of electrical interference. (Your next door neighbour installing a new TV, freezer or router could, for example, add to the interference picked up by your aerial). High winds can also knock your aerial out of alignment (or rain can get into the connections).
Start by checking that your aerial is still pointing in the correct direction (and that all of the connections are secure). Then, if the problem remains after retuning again, seek to improve your signal strength. Theoretically you should upgrade your aerial to something like this
http://www.maplin.co....ital-tv-aerial-221124
(and probably replace the cabling at the same) but in practice (given that you've had sufficient signal strength up until now) a simple signal booster should do the job. Asda and Tesco both sell them for under a tenner but this one from Maplin offers better signal gain:
http://www.maplin.co....rial-amplifier-223504
Chris
If your Freeview box asks you to choose between 'adding new channels' or 'replacing channels' (as mine does), you should select the 'replace' option. (You'll probably need to retune after following the advice below).
Now to the cause of your problem. It's simply insufficient signal strength.
Freeview channels are transmitted in 'bundles' (called multiplexes), with each multiplex using a different frequency. In an ideal world your TV aerial should have elements which are exactly the right length to 'resonate' with the incoming frequency. So, theoretically, you need a separate aerial for each multiplex. That's clearly impractical, so you use a single aerial which is only a 'rough match' to each of the frequencies (and is likely to be better at receiving some multiplexes than others). Your aerial resonates poorly with the frequency of the multiplex that bundles the missing channels together.
Further, the signal strengths at your aerial don't remain constant. They're affected by the 11-year sunspot cycle, individual solar flares, atmospheric pressure (and precipitation) and all sorts of electrical interference. (Your next door neighbour installing a new TV, freezer or router could, for example, add to the interference picked up by your aerial). High winds can also knock your aerial out of alignment (or rain can get into the connections).
Start by checking that your aerial is still pointing in the correct direction (and that all of the connections are secure). Then, if the problem remains after retuning again, seek to improve your signal strength. Theoretically you should upgrade your aerial to something like this
http://www.maplin.co....ital-tv-aerial-221124
(and probably replace the cabling at the same) but in practice (given that you've had sufficient signal strength up until now) a simple signal booster should do the job. Asda and Tesco both sell them for under a tenner but this one from Maplin offers better signal gain:
http://www.maplin.co....rial-amplifier-223504
Chris
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