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THE TRANSMISSION GALLERY
BLUNSDON
| Photos by Martin Watkins, Peter Bigwood and Neil White (commentary by Dan Glover and Martin Brown) | Page last updated: 2016-01-26 |
| Blunsdon is the former IBA site (later ntl) which serves the Swindon area with Local and national AM, FM and DAB radio The mast transmits AM and most FM services - DAB comes from the adjacent tower, see separate page. Virgin Radio comes from the ex-NGW site known simply as "Swindon" The site was originally built for Wiltshire Radio (which later became GWR and then Heart) in time for their launch on 12 October 1982. At that time it was not unusual for a hybrid AM/FM site to be established with the MF mast radiator also used to support a Band II array of some form. Christchurch is another example with a "twin Z" antenna. The station originally operated on 96.4 MHz (changing to 97.2 MHz on 9 October 1986) and 1161 kHz. The mast is 55 m overall with the centre of the Band II array at 52 m BBC Wiltshire Sound (which could not use the name "Radio" as it had already been taken by ILR) launched on 14 April 1989 using a new, directonal, array at 44 m. The horizontal yagis are on bearings 135 and 225 with a vertical dipole between, and maximum ERP on bearing 180. According to Ofcom data the horizontal and vertical components have the same ERP - which presumably means more power is fed to the dipole than the logs. As with ILR, the BBC local transmitter is line fed - at various times there has been a separate local programme for Swindon The BBC National services were added in July 1994. These are a relay of Oxford and use the two vertical logs at 35 m on bearing 180 Classic FM arrived in August 2002 - almost 10 years after the station's launch. The service shares the omnidirectional array at the top and relays Wenvoe (the receive antenna is on the "DAB" tower) Brunel FM (now Sam FM) launched on 2 September 2006 but uses a separate antenna on the other tower |
| Martin Watkins photos start with this overview, showing the MF mast and three Band II arrays. The yagi on the roof of the building receives the BBC National services from Oxford The satellite dishes provide the DAB programme feed - see separate page |
| From top to bottom: ILR/Classic FM, BBC local and BBC National |
| The "twin-Z" operates in a broadly similar manner to a Lindenblad array, giving mixed polarisation and omnidirectional coverage |
| The Band II array and its support pole forms part of the MF radiator - there is no insulator at the top of the main structure |
| Looking up we can just see the vertical dipole used by the BBC local station, between the two horizontal yagis. The BBC national services have a more directional coverage from the log periodics below We understand the there was a need to limit the BBC local signal (103.6 MHz) to the north to reduce interference with adjacent channel station BBC WM from Lark Stoke on 103.7 MHz. The yagis face roughly south west and south east. Radiation to the north from the diople will be limited by the mast. Ofcom data shows the same ERP for the horizontal and vertical components |
| Peter Bigwood's photos are from a slightly different perspective and show a couple of additional technical details... |
| The feeder for the top array runs down the main structure... |
| ...it looks as though the top array may have two independent feeders? The power divider for the BBC local array is just below the yagi on the left |
| With the entire structure being "live" there is the small problem of feeding 1161 kHz to the mast but decoupling the VHF transmitters. The "plumbing" shown above performs this function |
| Once more, from the top... Neil White's April 2015 photos are taken from a position to the east of the mast and give a different perspective |
| No change to the ILR/Classic or BBC arrays |
| There is now a substantial fence around the mast base |
| Peering through the main gate, the receive antenna for BBC national networks and a GPS cone - the building was extended when DAB was added |
Mangotsfield | Marlborough | Naish Hill
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