Metal in the Sky
- TV in Oxford
Introduction
In the days of VHF 405-line TV, reception
in Oxford was at first only available from Crystal Palace (well, at very
first from Alexandra Palace) and Sutton Coldfield (BBC), plus Croydon and
Lichfield (London and Midland ITV respectively). BBC reception on Band
I was fairly standard from either direction (mostly 2- and 3-element arrays
plus some larger). For ITV, large Band III arrays were common - the (even)
choice between Croydon and Lichfield depending on both location and preference.
During the 'second phase' Oxford became a primary service area with BBC
being transmitted from Beckley and ITV (Midland) from Membury, although
many forlorn 'double sixes' and a few 'double nines' survive to this day.
Now it is possible to receive reliable
(terrestrial analogue) UHF TV in Oxford from at least four different programming
regions.
Easy
There is a local main transmitter at Beckley
(2·8 miles from us in Old Marston) which most people in Oxford tune
to - it provides BBC South (Oxford), BBC-2, Carlton Central South, Channel
4 and Channel 5 (at lower power). We have a J-Beam Logbeam LBM2 array (19
feet high, in the roof) which gives perfect reception.
Standard
Reception from Hannington (32 miles exactly
South from us) is also good - it provides BBC South, BBC-2, Meridian Television,
Channel 4 and Channel 5 (at lower power). It is the transmitter of choice
in some parts of Oxford where the line of sight to Beckley is obstructed.
We have a J-Beam Multibeam MBM46 array (19 feet high, in the roof) with
a Labgear CM-series head amplifier which gives almost perfect reception
- an outside array would probably not need amplification.
Quite a few dual installations (Beckley
: Hannington) can be seen in Oxford. Before Channel 4 started, it was enough
to combine the two arrays with a diplexer; now, especially with the advent
of Channel 5, channel filters are really needed to avoid ghosting on the
Beckley signals.
Fringe
Fringe reception is fun! You never quite
know what to expect - the weather has a major influence on the signal -
sometimes the picture will only just stay put during the troughs of deep
fades and is very noisy, whilst at other times (usually during high pressure)
it can become almost noise-free. Even during the worst conditions, however,
reception from Sandy Heath and Crystal Palace is watchable, with colour
and NICAM stereo (if not always Teletext). The liveliness of fading, snowy
images with passing ghosts etc certainly improves the duller programming!
Reception from Sandy Heath (49 miles from
us and almost on our line of sight to Beckley), which provides BBC East,
BBC-2, Anglia Television, Channel 4 (Channel 5 is very weak), varies depending
on the weather. We have a Triax Unix 100 array (17 feet high, in the roof)
with a Research Communications ultra-low-noise GaAsFET head amplifier -
the array really needs to be put outside.
Reception from Crystal Palace (56 miles
from us), which provides BBC London, BBC-2, Carlton / London Weekend Television
and Channel 4, also depends on the weather. Channel 5 from Croydon is now
at about the same level. The John Radcliffe Hospital, perched on Headington
Hill, is directly on our line of sight - we must ask them to move their
buildings a few hundred yards to the side, although the hill should be
moved too. Consequently, we only have a refracted and/or scattered signal
and atmospheric effects are often very lively. We have an Antiference Extragain
XG21 array (30 feet high, above the roof) with a Research Communications
ultra-low-noise GaAsFET head amplifier. This was once knocked out during
a thunderstorm.
Anecdotally, Crystal Palace reception is
said to be relatively good in Rose Hill because it lines up with the M40
cutting through the Chiltern Hills. Looking at the map shows that things
are never that simple...
A quite small number of Crystal Palace
UHF arrays can be seen in Oxford, and most of these are probably disused
relics of the first BBC-2 service. We have only spotted a couple of 'definite'
Sandy Heath arrays. It seems that very few people are interested - or that,
like us, they prefer to put the hardware inside the roof.
Others
Reception from Sutton Coldfield (63 miles
from us) is also feasible as a fringe choice; but the programming (BBC
West Midlands, Carlton Central West) differs so very little from the local
Beckley output that we don't seem to watch it. Channel 5 from Lichfield
is at about the same level. At some locations to the South-West of Oxford
good reception from Mendip (71 miles from us: BBC West, HTV) is also possible.
During tropospheric 'lifts' the world is
your oyster (well, our Crystal Palace UHF system gives an East-South-East
window into Europe anyway). From Oxford, try Rowridge, Ridge Hill, Lark
Stoke, Mendip... for an idea of conditions. Then, of course, there is VHF
Sporadic E - another story, another page...
It is unfortunate that terrestrial digital
decoders are currently like hens' teeth, or we should have some idea whether
the experimental Crystal Palace service ever reaches Oxford. By the time
we can get one, digital will have 'gone national' anyway [update
25 November 1998: we have, and it has]. Finally, we await the new
Restricted Service Licence stations with interest [update 6 June 1999:
The Oxford Channel has just opened on Ch. 47].
Techie stuff
Combining the signals from high-gain systems
requires some care if one is to avoid unwanted ghost images from the off-beam
arrays. One also needs to take care not to overload high-gain amplifiers
with (very) strong signals from the local transmitter. However, it can
be done using channel filters, diplexers etc and the results are
well worth the trouble. There is no appreciable adjacent-channel interference
between Carlton/LWT (channel 23) and Anglia (channel 24).
Although it might be tempting to use a
single wideband array with a rotator, or perhaps just antenna switches,
the hassle-free and instant channel changes given by a permanent dedicated
system are greatly appreciated by viewers - especially when more than one
TV set is on!
Jon Godwin
Links
[End of document of 9 May 1998, updated
to 22 October 2001]