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In the last month the BBC quietly switched off AM radio transmitters to see if anyone noticed - and it seems not a lot of people did.

Four local radio stations had their medium-wave transmissions axed in the last few weeks. Essex and Hereford are now back on while Nottingham and Kent remain absent in the interest of seeing if any people are outraged - or if the transition to FM and digital radio has left the medium-wave bands to crystal-radio-clutching kids who really aren't worth the money.

The vast majority of AM stations are also broadcast on FM, slightly up the dial, and on DAB too. FM radio is in the government's sights, and AM is likely to be collateral damage in the rush to digital.

Transmitting the same radio station in four formats (AM, FM, DAB and over the internet) is expensive, and the BBC would love to save some cash by dropping AM as soon as possible, though not if lots of people are still listening. So the corporation replaced four local stations with a recorded announcement suggesting listeners phone in to report they'd noticed:

We asked the BBC how many calls it received, but the broadcaster just confirmed that BBC Radio Nottingham will remain off medium wave "because we want to assess the impact of a longer term switch off given the low number of response in these areas".

AM, or amplitude modulation, was one of the first forms of radio encoding, varying the strength of the signal over time to reflect the desired audio. It is primitive enough to be decoded with an unpowered crystal radio stuffed into a matchbox or printed into a postcard. But variations in signal strength from atmospheric or environmental factors are interpreted as desired sounds, so AM quality is variable to say the least.

Which, in Europe at least, prompted the move to FM - frequency modulation - which varies the frequency to encode the audio so the strength of the signal can change without ruining the sound. FM radio had to slide up the dial, as AM was already established in the medium-wave bands, but most listeners seem to have moved with it. Although medium-wave bands are full of radio it's bereft of listeners as the BBC is discovering.

FM radio is much more popular than AM, and car drivers in particular are reluctant to make the switch to the arguably lower-quality-but-certainly-more-expensive digital equivalent, which brings us to Blighty's Ministry of Fun.

Ed Vaizey, the minister for culture, communications and creative industries, announced the schedule for switching off analogue radio next year at the unveiling of "D Love", the animated character who'll convince us all that DAB is the way of the future.

D Love will visit our TV screens and radios as part of a £10m campaign running over the next two years. The cartoon will tell us we should be embracing the future, rather than clinging to the past, and clearing those valuable airwaves for something a little more profitable. ®

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