|BBC Radio 1, 2, 3, 4
BBC Radio Scotland
Former UHF Analogue TV (UHF Ch No)
Digital Terrestrial "Freeview" - UHF channel numbers
|97.9 88.3 90.5
92.7 MHz (also carries local Aberdeen,
Orkney & Shetland opt-out radio services)
BBC1/2 (22/28), ITV (25), Ch 4 (32) Now Discontinued
28 / 25 / 22 / 27 / 24 / 21
8 to 12 kW * see text
|All Photos By Dave Stephen and
additional information provided by Ian Anderson of SIBC 96.2 http://www.sibc.co.uk
The Bressay transmitting station in
Shetland was opened by the BBC on 15th April 1964 to bring VHF
monochrome television to the islands. There are two towers on the
site, one essentially for TV and one essentially for radio. VHF
television has now ceased but in 2004 Bressay transmits UHF analogue
colour television from BBC1, BBC2, ITV and Channel Four (but not Channel
Five) and UHF Digital Terrestrial Television (DTT).
The second tower is used for VHF/FM radio broadcasting and this
transmits the high power BBC national and local opt-out services
together with the Independent Local Radio station SIBC (Shetland
Isles Broadcasting Company). The programmes for SIBC were originally fed to the
Bressay site from the studio in Lerwick via a low power radio link on
102.2 MHz (20 watts - vertical), which also acts as a small filler for
the town. Since 1994, however, the feed from the studio to the
transmitter has been via U.H.F. (Ultra High Frequency) radio link. The 102.2 MHz
v.h.f. transmitter is now essentially a standby service that listeners
can retune to should Bressay fail, which has happened.
These details have been
provided by Ian Anderson of SIBC
kindly e-mailed us to confirm the technical details of the station and
also points out that SIBC uses the two vertically polarised Marconi
R1000 aerials seen in several of the photographs below. Thanks Ian!
The transmitting aerials used by the BBC radio services are the six
tiers of large "Coniex" crossed dipole aerial panels at the top of the
In SIBC's Ian Anderson's e-mail he also notes
that: "Your e.r.p. for SIBC
is undercalculated, although it is difficult for us to give precise
figures. If the BBC is "high power" we cannot be "low power"
since were are on parity with the weakest of the BBC services (the
variance in the Q of the aerial system means that the services erps are
not all the same) in some lobes, and no more than 4-5dB down in
general. It has been like that for 10 years, with 1 dB
increased reflection from the Orange metal work (just above) added a few
years ago. It just shows that a well placed dipole pair
with reflectors can be relatively efficient, even against eighteen
Coniex crossed dipole panels". Very many thanks to Ian
Anderson of SIBC for the very useful contribution and clarification.
The 4kW figure that I originally used are those published by The Radio
Authority and later Ofcom. I did, however, read in "Communication" (the
monthly publication of the BDXC - British DX Club) in around 1994/5 that
SIBC had been given authorisation to increase transmission power from
4kW vertical to 50kW mixed (i.e. 25kW (V) + 25kW (H)), making it
most powerful ILR station in the UK. Although the current
technical parameters published by Ofcom show the permitted maximum
e.r.p to be 50kW mixed, SIBC continues to use the two Marconi
vertical antennas and the power is now as Ian Anderson most kindly
From what Ian has written that the output from SIBC is
probably nearer to 8kW vertical on average (i.e. about 4dB down from the BBC's 43kW
mixed i.e. 43kW ÷ 2 = 21.5kW less 4dB = 8.6 kW).
This may change in the future as in 2012 SIBC hope to install a new
transmitter and have it combined into the main Coniex antenna system
used by the BBC's national stations.
photographs show the tower that carries the radio transmitting aerials:
The tower carrying
VHF radio aerials. The six stacks of Coniex mixed polarised aerial
panels that carry
high power BBC VHF/FM radio are positioned at the top of the tower.
Just above the Coniex panels there are UHF aerials which carry two of
the DTT (digital terrestrial TV) multiplexes.
The other digital terrestrial tv multiplexes (BBC, Freeview etc) are
carried via the main UHF aerials
on the other tower on the site.
A close up of the main mixed
polarised aerial panels for high power BBC VHF/FM
details two sets of aerials:
1/ Two horizontal log periodics (top right) that appear to be VHF
receive (RBR) aerials for BBC Radio
2/ Below the pair of Orange mobile phone aerial panels are two vertical
Marconi R1000 dipoles, (bottom left with white dipole centres)
reflector, that are used by the ILR station SIBC that produce near 8 kW.
A view from the
hill with the radio tower on the left and the television tower on the
|The following photographs, below,
show the tower that carries the main television transmitting aerials:
A close up of the main UHF GRP aerial cylinder and top mast light
Note the six VHF yagi antennas on the left hand side about one third of
the way up the tower, just below the mast light
A close up of two of the six VHF yagi antennas
Thanks to Dave Stephen for very kindly sending in these photographs.
|Continuing the subject of radio
coverage from the Bressay transmission tower, Ian Anderson of SIBC adds:
The e.r.p. of SIBC
is no worse than 4-5 dB on the BBC in some directions and parity in
others. The BBC's horizontal pattern is like the petals of a flower and
the parity is in the directions where we have a gain and they have a
In one direction
(roughly towards Lerwick) we have massive reflection of the tower (we
are low down on the tower so there is a lot of metal behind us, and to
the side) and Orange's metal work above added 1 dB when it was installed
by reflecting our signal downwards.
The Radio Authority
did a computer model and gave our maximum lobe as 9dB because of the
metal work, so that would be 16kW less feeder loss (c 1dB). We are
probably about 12.5kW max in that direction, which is only 3dB down for
the maximum of 25kW vertical that we are allowed. We usually quote
about 12.5 kW vertical towards Lerwick, Brae etc.
radiation is interesting. With no horizontal element, we are actually
less than 10dB down on horizontal, all because of reflections of the
tower, the hillsides and twisting in free space, giving about 1kW all
for free!!!!. We are also less prone to some kinds of multipath than
the BBC curiously.
When the hills are
wet from rain, the soaked peat also helps to conduct our signal over to
the back of hills. Normally there is increasing attenuation when the
declination behind a hill is greater than 7 degrees, but wet hills help.
Attenuation due to
mist and drizzle the short distance between Lerwick and Bressay,
combined with scatter reflection of the small droplets, can be as much
as 1dB. And when very large ship enters the harbour we can see a change
in signal strength from -3dB to 2dB. Recently a crane worked 100 yards
away and the same changes were witnessed.
The moral of the
story is that you can used scorched earth power like the BBC and lose it
all because local circumstances.
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