Surprisingly, radio attracts more listeners daily than TV attracts viewers.

This growth in radio use is set to explode as Digital Audio Broadcast coverage expands and DAB radio becomes more affordable.Digital Audio Broadcast has been around for several years and the BBC and Digital One commercial broadcasts are now well under way (see opposite).

Originally, DAB was introduced as a better radio system for mobile use. It meant reception could be snap, crackle and pop free the length and breadth of the country without constantly re-tuning and with each station on the same frequency across the country. The “Hi-Fi” fraternity soon identified the benefits of the high quality reception possible from DAB and broadcasters were keen to exploit the higher number of programme slots available, compared to the FM band II frequencies between 88 to 108 MHz.

DAB is currently used to broadcast some 50 radio stations in Band III between 216 and 230MHz though this may eventually expand to the end of band III at 240MHz. It is also proposed that local DAB transmissions will use the “L” band in the future.

Surprisingly, some equipment manufacturers seem to suggest that DAB signals need only a portable or indoor antenna, but those with experience of digital TV signals will know differently.

Receiving DAB requires a dedicated aerial for reliable reception in moderate to poor areas. DAB behaves just like digital TV reception where low signal level is expected. Impulse noise and poor carrier to noise ratio will cause lock ups in the audio stream just like lock ups in digital TV.

A basic outdoor DAB aerial usaully consists of of a half wave dipole mounted vertically. This is not a “DAB omni” although it does receive signals from all round 360°. In weaker signal strength areas a multi element array is required aligned to the nearest transmitter.

Most manufacturers offer traditional Band III “Yagi” antennas which will generally work adequately. However, the gain displayed by these models is not linear across the whole DAB radio band so the DAB multiplexes will arrive at different levels.

A popular option for installers over the last year has been the inexpensive LPVA DAB antenna, designed using log periodic technology. It has a flat 9dB gain right across all the DAB bandwidth as well as high directivity and superb front to back ratio for 'interferring signal' rejection. Its lightweight design and compact size also ensures low wind loading.

The MATV/IRS installer must also consider DAB when designing systems and specifying amplifiers. An amplifier must have at least a Band III input or when using a single input amplifier, it must cover the DAB frequencies. The FR channelised K series range includes a DAB filter with 14dB gain and 105dBuV output. It is particularly very effective in removing other unwanted frequencies, such as Public Mobile Radio which shares Band III.

The market has been slowed by the gradual expansion of coverage and the current high cost of receivers. However, new transmitters are coming on stream almost weekly and now cover nearly 80% of the population. The cost of receivers is expected to fall again this autumn so that by next year, tuners could be below £200, as the cost of the chipset reduces and the volume increases. Currently DAB radios can be purchased for under £300.

Tuning a DAB radio is frequency transparent. The user display only shows the radio station name not the frequency tuned.