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³ÉÈË¿ìÊÖ Radio Devon on 855 in Plymouth was switched off on 1 April 2007, so the frequency can be re-used for a trial of digital medium wave from the end of April.

While listeners can keep enjoying ³ÉÈË¿ìÊÖ Radio Devon on FM and DAB digital radio, there is currently nothing being broadcast on the old 855 frequency.

The ³ÉÈË¿ìÊÖ first started to use 855 in Plymouth in November 1978.

The first service to be broadcast was ³ÉÈË¿ìÊÖ Radio 4. When ³ÉÈË¿ìÊÖ Radio Devon started just over four years later, the frequency was transferred over to the new station.

This is the first time in a generation that nothing is being broadcast at that place on the dial – and that's quite interesting for the engineers involved in researching digital medium wave.

Whenever you're listening to your favourite programmes, the radio station you are receiving is not the only radio signal being picked up on that particular frequency.

Your radio has to make sense of a jumble of different signals, but most of the time the thing you want to hear – ³ÉÈË¿ìÊÖ Radio Devon – is louder than anything else and effectively drowns the others out.

At other times, especially on medium wave, you might hear the distant sounds of a foreign broadcaster underneath the programme you're trying to listen to.

For example, listeners to the old medium wave service on 855 may be familiar with the sounds of Spanish radio, as we shared our frequency with a transmitter for Radio Nacional de España in Murcia, Spain.

Not all of the other signals come from broadcasters. All sorts of other things generate signals which can affect your enjoyment of the radio.

Some of these – lightning strikes, and the background signals of the universe emitted by stars – are natural. While others, like the signals emitted by power lines and sparking electric motors, are man-made.

The engineering term for these signals is 'noise'.

Now that the Radio Devon signal has been turned off, our engineers are keen to find out more about the amount and type of this background noise. It's just not something which could have been measured whilst 855 was on-air.

So while we're working to get the digital medium wave transmitter ready, teams of engineers will be out in Plymouth and West Devon just listening to the noise created by the rest of the world.

The digital medium wave service starts on St George's Day, 23 April and will be the first of its kind in the UK.

Meanwhile, to keep listening to ³ÉÈË¿ìÊÖ Radio Devon in Plymouth re-tune your radio to 95.7 FM or DAB digital radio.