Radar System Engineering

f$Ec. 69] EARLY AIRCRAFT-WARNING RADAR 179
Measurements of angles of elevation above about 7° were ambiguous
on this so-called “A” system, and measurements of angles below about 1°
were inaccurate owing to the “flatness” of the height curve for these
small angles. The maximum usable angle of elevation was extended by
using two receiving antennas 90 ft and 45 ft high respectively (the “B”
system). Figure 6.17 shows the goniometer readings for the A and B
systems as a function of angle of elevation. The curves are plotted for a
flat site and-for antennas perfectly matched to their feeders. In practice,
the height curves for all stations were verified by an elaborate series of
test flights. Owing to irregularities of sites the height curves varied
considerably with azimuth, with the result that it was sometimes neces-
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& 120 - .of A system
$ 110
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Angleof elevat!onin degrees
F1~.6.17.—Height curves for CH station. Wavelength = 13,22meters.
sary to use half a dozen different height calibrations. Some stations
could measure height only in one or two favorable azimuths.
The operations involved in applying azimuth errors and interpreting
height measurements were performed automatically by a system of
standard telephone selector switches and kelays. The operator measured
r“ange by a pointer on the tube, azimuth by turning thp goniometer to
give zero response from the echo. Shel then pressed a button and the
grid reference (Chap. 7) of the target appeared on a board. The operator
then switched to height-finding, turned the goniometer again and pressed
a button, whereupon the height was displayed in front of the teller. If
the height measurement was ambiguous or unreliable, that fact was shown
by the machine, and the operator could try again on the “B” height
system. Operational use of radar information is discussed in Chap. 7,
The shortcomings of the CH system are fairly clear. Its long
wavelength necessitated the use of large and expensive towers. There
1After 1940almost all operators were women.