Co-Channel Interference

The weather forecast for this week is for the high pressure over the UK to maintain and even strengthen its position. This is the "ideal" situation for co-channel (sometimes called cross-channel or pattern) interference to occur while trying to receive a television transmission. With analogue tv this shows up as a pattern of wavy or horizontal lines on the screen. With digital tv, once a threshold has been reached, you lose the Mux you're trying to watch completely.

These events are caused by a powerful tv transmitter somewhere in mainland Europe (or elsewhere in the UK) being unusually received by your aerial owing to its transmissions being reflected by the atmosphere down to your aerial. In low pressure weather conditions such transmissions go in straight lines off into space.

Some enthusiasts like to receive distant tv transmissions and their forecasts are for Tuesday to Thursday of this week achieving the peak for such reception and therefore for co-channel interference to be more likely.

If you draw a straight line on a map from Wimborne to Rowridge and extend it beyond, it goes very close to Lille in France. There lies a powerful digital tv transmitter which includes transmissions on channels 21, 24 and 27, exactly the channels used by Rowridge for its three PSB (Public Service Broadcast) Muxes. If you find this week, or at any future time, that you lose any or all of these three Muxes, that transmitter could be the problem. The solution is to have your aerial rotated through 90 degrees so it is vertically polarised. I would advise waiting until after 18 April to have that done otherwise you will lose some stations in the meantime.