BBC RADIO BRISTOL

The map above shows the coverage area of BBC Radio Bristol from the original VHF/FM transmitter at Mendip and lower power relays at Ilchester Crescent and Bath. The map also shows the daytime medium wave coverage from the transmitters at Mangotsfield (1548 kHz) and Taunton (now operating on 1566 khz). Until late 2007 the station was operating a part time opt-out radio service for the county of Somerset, called BBC Somerset Sound, from the Taunton AM transmitter on 1566kHz medium wave.

In the summer of 2007 the BBC's transmission cotractors moved Radio Bristol's city 'fill-in' relay at Ilchester Crescent Bristol (94.9 MHz) to a new site on a tall tower high on Dundry Hill, at East Dundry Lane, overlooking the city. The Dundry Lane transmitter will provide a much enhanced coverage area compared to Ilchester Crescent.

This re-engineering of the 94.9 service was the first stage in a plan for the BBC to re-allocate the 95.5MHz transmitter at Mendip to the new BBC Somerset Sound radio station, with BBC Radio Bristol continuing on the enhanced 94.9 frequency for Bristol, South Gloucestershire and parts of North Somerset and also on 104.6 MHz from the Bath relay. A frequency of 103.6 MHz was also registered for BBC local radio at the Hutton transmission site, and brought into service at a later date to bring good reception to Weston Super Mare. Once all this work was completed, BBC Somerset Sound was split from BBC Radio Bristol on a full time basis in late, using 95.5 MHz from Mendip.

Once BBC Somerset Sound was allocated full time use of 95.5 from the Mendip transmission site, the station would have almost county wide coverage on vhf / fm. However there is a notable area of poor reception around Yeovil and this may be resolved by the installation of a low power fill-in relay transmitter. A frequency of 104.1 MHz is registerd with the ITU for this perpose. It is possible that Taunton may also be considered for a low power fill-in relay (possibly using 104.7MHz, which has also been registered with the ITU), in which case the transmitter scheme would be similar to that of the Somerset ILR station (Orchard FM)

Modifications to the Mendip Aerials for BBC Somerset Sound, local radio:

To avoid overspill of the newly separated BBC Somerset Sound Radio station into Bristol, the aerials on the Mendip mast, formerly used by BBC Radio Bristol, were modified. The north facing aerial panels were removed and the radiation pattern changed so as to retain coverage into Somerset, but condsiderably attenuate signals into the city of Bristol.

Initially, when transmitting Radio Bristol, the BBC rated the VHF transmissions from Mendip on 95.5MHz at 9kW maximum effective radiated power (presumably in the direction  of Bristol). After the aerial modifications were made the BBC rated the transmissions as 5kW maximum effective radiated power - e.r.p. -  in the direction of Somerset.

Looking at the vertical radiation pattern the null towards Bristol  is 15dB down on on the maximum power - i.e. about 0.16 kW towards Bristol. That's about 30 times less power than that directed towards Taunton. The null is 19dB at 10 degrees in the horizontal pattern.

It is unknown at present, but the BBC could commission additional low power relays at Cheddington for Yeovil, as used for commercial radio in Somerset, or maybe a site closer to the town (e.g. Coker Hill). In Taunton the BBC investigated Staple Hill, as did the IBA for the ILR station, but it is more likely that a site closer to, or indeed in the town would be considered - as was the eventual case for the ILR station - if a relay transmitter is indeed considered. Additionally there is a chance that the BBC could consider a relay for Minehead to in order to provide a truly county wide vhf / fm service, but all of this is speculation at this stage (summer 2007).

Pixel plot showing the predicted coverage of the low power
BBC National FM Radio relay transmitter at Hutton

The BBC national radio services are radiated at 40 watts with vertical polarisation from a highly directional aerial.
The plot is produced using the directional data supplied by the BBC and Ofcom.

Pixel Plot showing predicted coverage of (ILR) Commercial Radio in Somerset
from the very directional aerials on the Mendip mast. 4kW, 213 metres a.g.l.

The pixel plot above shows the very directional service (4kW max e.r.p.) on 102.6 MHz from Mendip for ILR Somerset (Orchard FM etc).  The two low power fill-in relay transmitters at Taunton and Cheddington are also included in this map.  There is a very low power relay for Taunton located at the former Orchard FM studio site on a small mast within the grounds.  It is only 0.07 kW and re-inforces the signal in some parts of Taunton on 96.5 MHz.  There is another relay at Cheddington which provides better reception in the South of the transmission area to the South and West of Yeovil. This uses 97.1 MHz with a power of 0.4 kW.

[ Also see the AVON page ]

Above:  The expected coverage as predicted by the RadioMobile plotting application
for ILR Bridgwater - BCRfm.  Transmitter power is 100 Watts verically polarised from
a transmitter in the town, frequency is 107.4 MHz.

The small scale station for Yeovil uses two transmitters; 250 Watts from Windwhistle Hill for the West of
the area on 106.6 MHz (solid green area) and a 250 Watt transmitter at Coker Hill for the East of the
area on 105.6 MHz (solid blue and blue outline).

ILR WESTON-SUPER-MARE  (1077 WFM / Star 107.7. / Star etc)

ILR MINEHEAD (102.4 Quay West Radio / Star etc)