Radar System Engineering

226 THE EMPLOYMENT OF RADAR DATA [SEC. 75
EXAMPLES OF RADAR ORGANIZATIONS
In the following sections are given very brief sketches of a few
radar organizations with which some experience has been obtained. The
systems described are, for the most part, necessarily those set up in wartime
for the purposes of war, and to this extent do not represent useful
models for peacetime radar organizations. It will, however, be instructive
to consider briefly a few typical systems.
7.6. Radar in the RAF Fighter Command .-Just as the first radar
equipment to be used in operations was that installed for the air defense
of the British Isles, so the first operating radar organization was that of
RAF Fighter Command, the user of this equipment. When the organization
was fully developed, the number of people in? olved in the interpretation
of the radar information and in making use of it was comparable
to the number required to obtain it.
Organization of the Home Chain.—It has been mentioned in Sec. 6..9
that the performance of CH stations depended very much on the nature
of their sites. Moreover, owing to a shortage of trained men and to the
difficulties involved in maintaining equipment of this kind in wartime,
the antenna systems were often badly installed and inadequately maintained.
In consequence, large errors in apparent azimuth were very
common; most stations had errors of 10° or 15°, and errors as large as 30°
were not unknown. The method of measuring height depended on
reflection of the received waves from the ground, and almost invariably
the height calibration of a station was different along different azimuths.
Each station had to be checked and calibrated both for height and azimuth
by an elaborate and difficult series of test flights.
The complicated nature of the corrections necessary on each aircraft
plot, and the requirement for speed and accuracy in applying these corrections,
led the British to design and install what is perhaps the first
device intended for assistance in the use of radar data, as opposed to the
gathering and display of that data. This is the celebrated “fruit
machine, ”l a complicated calculating machine made up of standard
telephone selector switches and relays. The operator measured the
range of the target by setting a marker to the echo on the .4-scope. She
then turned the goniometer until the echo disappeared, and pressed
buttons transmitting range and apparent azimuth to the fruit machine.
The machine automatically applied the appropriate correction and
deduced the true azimuth, multiplied the target range by the sine and
the cosine of this true azimuth, added in the rectangular map coordinates
of the station itself, and deduced the coordinates of the target. This
: It was named after the English equivalent of the American slot machine used for
gambling.