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AVON & BRISTOL


BBC RADIO BRISTOL


BBC map showing the coverage area of the BBC Radio Bristol transmitters

The map above shows the coverage area of BBC Radio Bristol from the original VHF/FM transmitter at Mendip (95.5 MHz at 9kW) together with the 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 operated 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 2007/8 BBC Somerset Sound split from BBC Radio Bristol on a  full time basis and gained a stand alone FM transmitter - Mendip on 95.5 MHz. To effect this, in the summer of 2007, the BBC's transmission contractors moved the Ilchester Crescent Bristol fill-in relay (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 site provides a much enhanced coverage area compared to the old 'fill in' relay site at Ilchester Crescent.

The map below shows the predicted coverage area (green) for good reception from the 94.9 Mhz  transmission from the new site at East Dundry Lane. The transmitter uses an aerial located at the top of the tower using 500 watts with vertical polarisation and, unlike all the ILR services for this area, has a rather less directional radiation pattern, as indicated by the Ofcom technical parameters.

It is interesting to campare this plot with the one for ILR Bristol FM3 (Jack FM 106.5 etc) which uses the same equivalent power, but with slant polarisation and a very directional yagi transmission antenna which is six meters lower than the antenna used by BBC Radio Bristol (see further down this page).

BBC Radio Bristol from East Dundry Lane - 94.9 MHz - 500 watts - Vertical Polarisation
BBC Radio Bristol from East Dundry Lane on 94.9 MHz.
Transmission power is 500 watts vertical polarisation.
Plotted using the directional characteristics published by Ofcom.


BBC Somerset Sound splits from radio Bristol and is allocated the Mendip transmitter on 95.5 MHz while Radio Bristol gets a better transmission site for their main 94.9 MHz transmitter:

The re-engineering of the 94.9 MHz service for Bristol (moving from Ilchester Crescent to East Dundry Lane) 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. BBC Radio Bristol continued on the enhanced 94.9 frequency for Bristol, South Gloucestershire and parts of North Somerset. Radio Bristol also being transmitted 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 purpose. 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).

See photographs of the East Dundry Lane tower at MB21.co.uk  HERE

BBC Radio Bristol - East Dundry Lane - Antenna Pattern (V)
BBC Radio Bristol - East Dundry Lane - Antenna Pattern (V)



Map. BBC Radio Somerset from Mendip
The Coverage Area of BBC Somerset Sound from the transmission site at Mendip.
5kW maximum e.r.p, Mixed Polarisation, Directional Pattern, Aerial System at 246 metres a.g.l.



BBC Somerset Sound Mendip Aerial Vertical Polarisatio Radiation Pattern
BBC Somerset Sound - Mendip Aerial - Vertical Polarisation Radiation Pattern

BBC Somerset Sound - Mendip Aerial - Horizontal Polarisation Radiation Pattern
BBC Somerset Sound - Mendip Aerial - Horizontal Polarisation Radiation Pattern




BBC RADIO BRISTOL VHF / FM RADIO RELAY STATION AT HUTTON - 103.6 MHz
BBC Radio Bristol VHF / FM Relay station at Hutton
Pixel plot showing the predicted coverage of the low power VHF / FM relay station for
BBC Radio Bristol on 103.6 MHz from the relay transmitter at Hutton

BBC Radio Bristol is radiated at 50 watts with vertical polarisation from a directional aerial. The plot is produced using the directional data supplied by the BBC and Ofcom.



BBC HUTTON NATIONAL VHF / FM RADIO RELAY STATION
Hutton vhf fm BBC radio coverage
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.




ILR BRISTOL FM1 - (Radio West - GWR FM - Heart FM etc)


IBA map for ILR Bristol with Wiltshire showing the combined coverage area of the
Dundry Hill, Naish Hill and Blundsdon v.h.f. / f.m. transmitters.

The Dundry v.h.f. / fm transmitter has since been increased from 0.5 kW to 2kW and the coverage will be slightly wider, as the pixel plots from RadioMobile predict below:

N.B. In September 2007 GCap/GWR (now Heart West Country) opened a new relay transmitter on 103.0 MHz to cover the town of Weston Super Mare which receives poor signals from the Dundry transmitter site. See photographs of Dundry Hill at MB21.co.uk  HERE


Bristol ILR-1 - GWR / Heart Westcountry - Dundry Hill 2000 watts
Pixel plot showing Dundry Hill  2.0 kW - expected area of good reception
ILR Bristol FM1 (GWR / Heart West Country etc)

Bristol ILR1 - Heart West Country -  Dundry Hill - Antenna Pattern 1kw Vertical
Bristol ILR1 - Heart West Country -  Dundry Hill - Antenna Pattern 1kw Vertical

Bristol ILR1 - Heart West Country -  Dundry Hill - Antenna Pattern 1kw Horizontal
Bristol ILR1 - Heart West Country -  Dundry Hill - Antenna Pattern 1kw Horizontal

See photographs of Dundry Hill at MB21.co.uk  HERE



Weston Super Mare relay at Worlebury Hill
Weston Super Mare FM Relay Transmitter for Bristol ILR-1 (Heart West Country)

In September 2007 GWR opened a new relay transmitter at Worlebury Hill to bring coverage to Weston Super Mare, an area of the TSA that has always had little or no coverage from the main transmitter at Dundry Hill. Mixed polarisation is used with power of 50 watts vertical plus 50 watts horizontal. Radiation pattern is 135 degrees from an aerial mounted 38 meters high on the Worelbury Hill tower. ILR Bristol FM1 (GWR / Heart etc)

Pixel plots use the detailed transmission parameters and data supplied by OFCOM.


ILR SOMERSET / YEOVIL AND TAUNTON (Orchard FM / Heart West Country etc)

Mendip ILR Somerset coverage map
Pixel Plot showing predicted coverage of (ILR) Commercial Radio in Somerset from the very directional
aerials on the Mendip mast. 4kW, Mixed Polarisation, Aerial System at 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 transmitters at Taunton and Cheddington are not included in this map. Due to variable reception around Taunton and Yeovil, additional low power relay transmitters have been installed to reinforce coverage.

The very low power fill-in transmitter for Taunton is located at the former Orchard FM studios on a small tower within the grounds.  It is only 0.07 kW and re-inforces the signal in some parts of Taunton on 96.5 MHz.  The other transmitter is a relay of Mendip located at Cheddington and provides better reception in the South of the transmission area to the South and West of Yeovil using 97.1 MHz with a power of 0.4 kW.

ILR Somerset launched in 1989 with Orchard FM providing the local radio service.  Since their transmitter was also located at the Mendip mast, along with BBC Radio Bristol, some listeners may have been forgiven for thinking that the ILR station may have enjoyed similar coverage to Radio Bristol.  However the effective radiated power is only 4kW maximum. (compared to 9kW for the original BBC Radio Bristol transmissions - which have now changed). Commercial radio from Mendip is highly directional towards to South West with a 17dB reduction towards Bristol in the North to avoid a programming overlap with the existing ILR station there.  his arrangement also avoids possible interference to the ILR station Fox FM in Oxford (now Heart Thames Valley) which also uses 102.6 MHz.

See photographs of the Mendip mast at MB21.co.uk  HERE
See photographs of the Taunton transmitter at MB21.co.uk  HERE


SEVERN ESTUARY INDEPENDENT REGIONAL RADIO (Galaxy 101, VIBE FM, KISS FM etc)

Mendip 40kw directional coverage for Kiss 101

Mendip 40kw directional coverage for Kiss 101
Coverage Map for the Severn Estuary Independent Regional Radio Station (Kiss FM)

The image above is of a pixel plot showing the highly directional service (40kW max e.r.p.) from Mendip on 101.0 MHz for the Severn Estuary Independent Radio service (Kiss FM etc). It can be seen that Bristol is poorly served and this is the reason for the low power relay on 97.2 from a 0.2kW relay transmitter at the concrete B.T. tower at Pur Down for Bristol city centre.


Mendip Aerial Pattern
The highly directional aerial radiation pattern for the Severn Estuary
regional radio service from Mendip

On paper the 40kW e.r.p. (effective radiated power) used by the regional Independent Radio station for the Severn Estuary looks extremely impressive.  However the transmitting aerials employed have very high gain and so have an extremely directional pattern that only allows the maximum 40kW to be directed in a beam towards Wales between a bearing of 300 and 320 degrees.  All other areas receive a much lower power signal.  There are other smaller peaks at bearings of 20 to 40 degrees, 120 to 140 degrees and 220 to 230 degrees.  In all other directions the effective radiated power is only about 0.4kW, a 20dB reduction over the main beam. 

The 40kW beam to the North West is obviously designed to penetrate the Welsh valleys, and the drastic reduction in signal towards the London area in the East is to prevent interference to the INR1 transmitter at Wrotham on 100.9 MHz (Classic FM).

The poor signal in Bristol is overcome by a low power 0.2kW relay station sited on the concrete BT link structure on Pur Down using 97.2 MHz.  The predicted coverage from this low power relay is shown below:

Pur Down Relay - Bristol coverage map for Kiss FM on 97.2 MHz (Also Classic FM on 101.4 MHz) 0.2 kW
Pur Down Relay Transmitter on 97.2 MHz FM

Some areas of Bristol may receive a better signal from the Severn Estuary Independent Radio Station (Vibe FM etc) from this low power relay transmitter at the concrete BT tower on Pur Down.  Power is 0.2kW mixed polarisation, frequency is 97.2 MHz.

See photographs of the BT tower at Pur Down at MB21.co.uk  HERE

Bristol Regional Radio Relay of Kiss FM on 97.2 - Pur Down - Antenna Pattern 0.1kw Vertical
Bristol Regional Radio Relay of Kiss FM on 97.2 - Pur Down - Antenna Pattern 0.1kw Vertical

Bristol Regional Radio Relay of Kiss FM on 97.2 - Pur Down - Antenna Pattern 0.1kw Horizontal
Bristol Regional Radio Relay of Kiss FM on 97.2 - Pur Down - Antenna Pattern 0.1kw Horizontal


ILR BRISTOL FM2 - (107.3 FM The Breeze etc)

Pur Down Coverage - 660 watts mixed polarisation
Predicted Coverage Area for Bristol FM station ILR-2 (Breeze FM 107.2)

The transmitter used by the second Bristol ILR station (107.2 FM The Breeze etc) is located on the concrete BT tower at Pur Down - together with lower power relays for INR1 (Classic FM) and the Severn Estuary Regional station (Kiss FM). 

For this service the ILR-2 transmitter uses 0.66 kW directional and the pixel plot above indicates where good reception may be possible in and around the city.

See photographs of the BT tower at Pur Down at MB21.co.uk  HERE

Bristol ILR2 - The Breeze 107.2 - Pur Down - Antenna Pattern 0.5kw Vertical
Bristol ILR2 - The Breeze 107.2 - Pur Down - Antenna Pattern 0.5kw Vertical
Horizontal power is 0.16kW


ILR BRISTOL FM3 (Jack FM formerly Original 106 etc)

Original 106.5 radio coverage map
Coverage area of predicted good reception for ILR Bristol FM3
Jack FM 106.5 MHz  (formerly Original 106).

This station uses the same site as BBC Radio Bristol at East Dundry Lane but utilises a different and more directional aerial which is six meters lower down the transmission tower: The ILR3 transmitter uses highly directional slant polarised yagi aerials to restrict coverage to the south. Power is effectively 500w vertical plus 500w hortizontal.

See photographs of the East Dundry Lane tower at MB21.co.uk  HERE

Bristol ILR3 - Jack FM 106.5 - East Dundry Lane - Antenna Pattern (V)
Bristol ILR3 - Jack FM 106.5 - East Dundry Lane - Antenna Pattern 0.5kW Vertical

Bristol ILR3 - Jack FM 106.5 - East Dundry Lane - Antenna Pattern Horizontal
Bristol ILR3 - Jack FM 106.5 - East Dundry Lane - Antenna Pattern 0.5kW Horizontal

ILR BATH (Bath FM etc)

Bath vhf FM coverage


The ILR station for Bath uses one of the broadcast towers located on Bathampton Down.  There are two towers here, the main one is used to relay television signals and BBC national radio stations along with a relay for INR1 (Classic FM) and the FM1 ILR station (GWR).  ILR Bath - Bath FM - also uses this tower.  The aerial is mounted at a height if 41m a.g.l. and transmits a directional signal across Bath with a power of 0.1 kW mixed polarity.


Roddy Jenkins adds:

Thanks for your excellent Mendip coverage maps.  I thought I might just add the following information. The Bristol ILR service of GWR FM can be picked up just South of the Mendip mast (ie the Safeway car park in Glastonbury!) on 96.3 MHz.  Orchard FM's base above the M5 motorway outside Taunton, in what was once a large family residence, obviously has some sort of feed to the Mendip mast.  I seem to recall a large satellite dish in the back garden facing South West, but seem to recall that this was for IRN (?)

The BBC Somerset Sound frequency was recently changed from the original frequency of 1323AM to 1566AM, to avoid interference from Voice of Russia.  The link below gives the story:


http://news.bbc.co.uk/1/hi/england/2349767.stm

On the television front, Mendip's television coverage extends right down into mid Dorset with the Cerne Abbas relay, thus Dorset is served by three different regions West (Mendip and relays); South West (Stockland Hill and relays); and South (Rowridge and relays).
 

Also, when we lived in the foothills of the Mendips in the early to mid 1970s, we couldn't recieve signals from the Mendip mast; instead we had to pick up BBC and HTV Wales from Wenvoe outside Cardiff. Even today here in the south Somerset village of Keinton Mandeville, we can in effect pick up three regions - West, Wales, and South West.  I suppose that if I was to erect a large mast on the roof and point an aerial towards the south coast I'd probably pick up BBC South and Meridian transmissions as well.

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