Spells of interference started over the weekend and are expected to last into the New Year. Southern England and Wales have seen the worst impact so far.
High pressure and temperature inversions can cause a duct in the atmosphere allowing terrestrial TV and radio signals to travel further and interfere or cancel out reception of normal TV and radio services. It comes during a peak fortnight for TV viewing, with broadcasters showing seasonal specials.
Who is affected?
It affects viewers with Freeview, plus some channels on hybrid services including BT TV, TalkTalk TV and Plusnet TV, which use the terrestrial TV signal for some services. Sky, Freesat and Virgin are unaffected. The problem manifests itself through pixelatation or weak/no signal messages. For some viewers, only certain groups of channels may be affected.
Some Freeview HD channels are more prone to interference, because they are broadcast at lower power and on a single frequency network.
On the radio, listeners to FM and DAB radio can be affected by interfering stations, which on FM can heard in the background. On DAB, interference causes audio glitches or loss of signal.
What to do...
TV
Affected viewers should not retune. There are no changes to Freeview transmissions and no scheduled work is taking place on the network over the holiday season.
Once conditions change, services should automatically restore themselves.
However viewers who do mistakenly retune may lose channels from the list, or end up receiving weaker, out-of-region or foreign channels in their channel list as a result of the atmospheric conditions and will be forced to keep retuning until all services are restored.
Following changes to the Freeview signal, viewers who frequently have this problem should contact a local aerial installer for advice. In some locations including East Kent, new transmitter sites have gone live, enabling households to reposition their aerial for a better reception.
Radio
FM listeners may be able a clearer version of their desired station on another frequency. DAB uses single frequency networks, retuning will not resolve issues. Listeners may be able to stream their chosen station online until conditions change.
Are mobile signals affected?
Mobile networks are also terrestrial networks and use the same frequency bands that were previously used for television. In different ways, they're also susceptible to anomalies in reception, including a greater likelihood of locking onto a foreign mobile network near borders.
Further information about TV reception issues caused by atmospheric conditions can be found on the BBC website or via Freeview.
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