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The
Authority's station on South Norwood Hill near Croydon serves 13.5 million
people in the London area, nearly a quarter of the population of the United
Kingdom.
The
London area is relatively flat except for the North Downs some twenty-five miles
to the south and the ridge of the Chiltern Hills some thirty miles to the west
and north. Topographically it presents no serious transmission problems;
indeed, the difficulty is to find high ground close enough to the centre of
London on which to construct a station. The choice rests between the 400ft
ridges of Muswell Hill (Alexandra Palace) in North London and Crystal Palace in
South-East London. In 1935 the BBC had chosen Alexandra Palace as the site
for its original London television station, but twenty years later they moved to
a new station at Crystal Palace. In the interests of good planning the
Authority decided to locate its first station near this site.
A
suitable open space for the construction of a small compact station which could
be brought into operation with the least delay was found just a mile away on
South Norwood Hill. The single 10kW transmitter, the first in Band III set
constructed in this country, was a laboratory prototype. The aerial was an
experimental 8-stack omni-directional vertically polarized array, supported on a
200ft tower of virtually 'stock' design. The first Independent Television
programmes were transmitted from this station on 22nd September 1955. With
an effective radiated power (e.r.p.) of 60kW (peak white vision) and 15kW
(carrier sound) the potential population coverage was about 11 million.
After some months a second fully-engineered production 10kW transmitter was
installed as a standby, and a little later further equipment was installed as a
standby, and a little later further equipment was installed to enable both sets
of transmitters to be operated in parallel in order to double the station's
power.
In
due course the Croydon station would have to be given a higher tower and a new
aerial system with directional characteristics tailored to give the optimum
performance. Meanwhile engineering effort was devoted to expanding the ITA
network of stations to meet the fast-growing public demand for Independent
Television programmes in other parts of the country.
The
completion of the BBC's high tower at Crystal Palace allayed any fears that the
mutual reflection of signals radiated from the two towers just a mile apart
might be harmful to reception, and in February 1959 the ITA obtained Government
approval to erect a higher tower and directional aerial at the Croydon
site. By the end of 1962 Croydon was transmitting from its slim new 500ft
tower and radiating an effective power of about 400kW directed to the
north-west, with 50 to 250kW e.r.p. in other directions, the strength of signal
being determined by the requirements of topography and the avoidance of
co-channel interference with other ITA stations and television services of other
countries. The improved performance of the Croydon station in 1962
extended the ITA's London area coverage to include a population of 13.5 million.
The
Authority is a present considering plans for a new station building and the
replacement of the transmitters at Croydon.
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