Technology: Carving Up the Dial

Clive Glover investigates airwave allocation

In the last issue of TX Radio Today, I looked at how the VHF/FM band is divided up for different services across the whole of the country. This time I'll look at how room could be found for new radio services in London and the surrounding areas, including the Government's own ideas from the Green Paper.

By far the biggest demand for licences for new stations will inevitably come from London and the South East. 177 of the 266 applications for experimental licences came from this area and, as regular TX readers will know, London has by far the largest number of unlicensed stations!

It isn't possible to say exactly how many new stations could be on the air as much will depend on where they're located and how powerful they are. However, we can make some educated guesses. As I explained in the last article, parts of the VHF/FM band are currently allocated to Land Mobile services (Police, Fire, Gas, etc.). After their removal, in two stages in 1990 and 1995, these sub bands will provide room for two national networks and perhaps 50 or so low-powered stations in London. But not until 1996!

While it would be possible to accommodate many small stations (say, up to 10 watts and covering a five km radius) it is much more difficult to accommodate many medium (say, up to 250 watts — a 25km radius) or high-powered (over 250 watts) ones. If everyone wanted to cover the whole of London there might only be a handful of extra stations — and at the expense of scores of smaller ones. However, parts of the VHF/FM band are only suitable or small stations, as shown below.

Public Mobile Sub-band (87.5 — 88.0)

One of the main surprises of the Green Paper was the suggestion that this sub-band (used mainly by taxis) could be used for neighbourhood services — very small, low-powered stations. There will be some problems clearing existing users and many radios wouldn't be able to receive some frequencies, but perhaps 15-20 stations could operate throughout London and the South East.

National Sub-band (88.0 — 94.6)

There are three national services within this sub-band. Radios 1/2, 3 and 4. The BBC may have to give up one network for a commercial service (but I suspect they will prefer to give up the network allocated for Radio One from 1990). Each network comprises very high-powered stations and local medium powered relays. The main high power transmitters for London and the South East are at Wrotham Kent, using 240KW each. Radio 1 and 2 share 89.1, Radio 3 is on 91.3 and Radio 4 is on 93.5.

Additionally, there are relays for each service at Guildford. Caterham and Kenley. This means that a number of small / medium powered stations could be fitted into these sub-bands throughout London without causing any unacceptable interference. As all the relays are south of the Thames, slightly more stations could be located north of the river. Perhaps 20 to 30 stations could be accommodated altogether in this sub-band.

Local Radio Sub-bands (94.6 — 97.6 & 102.1 — 104.5)

These sub-bands are intended for medium or high-powered BBC Local Radio and Independent Radio services. These are equally suitable for medium-powered services, such as community of interest stations. About 11 such stations could be fitted into the existing sub-bands throughout London and the South East, but eliminating simulcasting (suggested by the Green Paper by 1995) could increase this to perhaps 20.

Neighbourhood Radio (105.0 — 108.0)

Because this part of the band is next to the sub-band used by aircraft navigation beacons, it is only suitable for very small neighbourhood services — and even these could be restricted near to one of the airports. Perhaps 50 to 60 of such services, covering a radius of up to 5 km could be accommodated throughout London and the South East.