Radar System Engineering

176 THE GATHERING AND PRESENTATION OF RADAR DATA [SEC.. 69
reporting system for the greater part of the war. At the very end of the
war the system was used to plot V-2 rockets. The great success of the
equipment, which saved the country from defeat during the Battle of
Britain, had an important effect on the course of radar development. It
called at ten tion to the revolutionary usefulness of radar in modern air
warfare, but at the same time it tended to freeze operational thinking
ccmcerning radar along lines of the static defense which was all that the
CH stations could provide.
The main Chain operated at frequencies between 22 and 28 Me/see.
In spite of the disadvantages inevitable in any system operating on so
low a frequency, the choice was made deliberately after consideration of
the tubes and techniques available at the time.
‘(Throughout the whole of the development period the small team who were
responsible ruthlessly sacrificed all refinements, elegancies and versatilities in
the desperate need for something to be going on with. They never turned aside
from their cult of the third best—(’ The best never comes, the second best comes
too late.” 1
At the frequency used, strong reflections from the ionosphere occur,
and an extremely low repetition rate of 25 pps was used in order to ensure
that ionospheric echoes were not confused with echoes from aircraft
targets. The repetition rate could be reduced to 12.5 pps when ionospheric
disturbances were unusually troublesome.
The pulse width could be varied from 6 to about 25 ~sec and the
receiver bandwidth could be changed from 50 to 500 kc/see. In normal
operation the pulse length was about 12 ~sec and the bandwidth 150
kc/see, The final design made use of continuously evacuated transmitting
tubes with uncoated tungsten filaments, whose c-w power output was
about 80 kw. Peak pulse power using these tubes was about 150 kw;
later, it was increased to about one megawatt. Both transmitters and
receivers were massive and elaborate. They were housed in separate
bombproof buildings, usually about half a mile apart.
Separate antennas were used for transmitting and receiving. The
main transmitting antenna was an array, usually of six dipoles with
suitable tuned reflectors, hung between two gantries on a 350-ft steel
tower. These towers were usually installed in sets of three in order to
provide spare antennas and standby frequencies. RadiaLion from the
transmitting antenna floodlit a quarter-sphere in front of the station, the
qreater part of the energy being confined within 20° of the horizontal
and within approximate y t 50° of the main “line of shoot. ” Enough
1Sir R. A. Watson-Watt, “ Radar in War and in Peace,” Nature, 166, 319-324,
(1945).