Travelling from West Cornwall to London, Gold is available until the Devon border. Then my radio will not find the station for most of the way from there.
The issue of losing reception of stations on car or train journeys is one which many listeners will have experienced and doesn’t only apply to Gold or the particular trip you mention.
Digital radio stations in the UK are mainly transmitted on national or local multiplexes.
A national multiplex like BBC National DAB covers 97% of the UK using 415 digital radio transmitters. This means that as you drive from West Cornwall to London your car radio will pick up the strongest signals on the way. As you travel you’ll continue to hear a station like BBC Radio 6 Music. The selection of stations is the same whereever you are in the country.
A local multiplex like Cornwall, which carries the Gold radio station, has good coverage in the county using 12 transmitters. Travelling from west to east your DAB radio will use these transmitters and you’ll continue to hear Gold. Local multiplexes have unique station line-ups, often mirroring the local stations available on FM. In Cornwall this would include BBC Radio Cornwall and Pirate FM.
When you cross the border between Cornwall and Devon on the A30 or A38 you’ll leave the coverage area for the local Cornwall multiplex. Devon has its own local multiplex which carries Gold, but you may need to retune to continue hearing the station. This should be available until you reach the border with Somerset.
Somerset also has its own local digital radio multiplex, but it does not carry Gold. Once you leave the coverage area of the Devon transmissions you’ll no longer be able to receive Gold. However, you would receive Gold again in Berkshire and in London as it is transmitted on DAB there. You may need to retune each time to continue receiving Gold as you lose the signal from the previous area.
This example can be applied to many radio stations in various parts of the country. If you tuned into Magic Soul in Newcastle you would continue to hear it travelling south through Teesside. Once you crossed into North Yorkshire you would lose the station, as it’s not carried on that local multiplex. Magic Soul would next be available in Leeds.
For local radio stations this arrangement makes sense, as you would not expect to be able to listen to BBC Radio Cornwall all the way to London. However, some national radio stations like Gold and Magic Soul are transmitted on local digital radio multiplexes. The broadcasters will have their own reasons for taking this approach, which could be due to capacity or the cost of national transmissions.
Other reasons for losing stations on journeys
Although digital radio coverage has improved in the last few years there are still areas with little or no DAB coverage. If you were to drive from North Yorkshire to Carlisle over the North Pennines you would lose many digital stations before picking them up again in Cumbria. This is due to a lack of coverage for villages and towns like Alston.
There are small areas in otherwise well covered areas where a DAB digital radio signal is lost. This is sometimes apparent when driving in a dip or a certain part of a town.
Hybrid radios which aim to avoid this problem are starting to appear in new cars. These radios have the ability to switch between different platforms to continue receiving the same station. An example might be switching from digital radio to streaming over 4G when the DAB signal is lost and switching back when DAB coverage is sufficient again.