I was listening to BBC Radio 5 (I don't do that very often) as I drove down the M1 motorway in the UK last month. As I neared London the sound-quality deteriorated noticeably, then once I got to the M25 ring-road, it became unlistenable-to, fading out altogether just as I hit the Dartford Crossing. Why is this? The station only seems to be available on AM, but surely London's able to receive it properly?

Radio 5 is a digital station which the BBC started as an AM one.Its associated channel is Radio 5 Sports Extra, which enables the BBC to cover two sporting events on digital at the same time. The AM is kept going to serve people using non-digital car radios and portables It's on two frequencies,909 and 693.Which is better is iffy. In Cambridgeshire, it depends on which bit of the county you are in and round here in the south of the county I find myself switching from one to the other The Dartford crossing must be such a place.

That is REALLY interesting. Many thanks.