Radar System Engineering

284 ANTENNAS, SCANNERS, AND STABILIZA TIOA’ [SEC.9.12
data are transmitted as voltages induced in synchros.’ There is, for
instance, a synchro generator built into the AN/APQ- 13 scanner shown
in Fig. 9.8 which revolves 10 times for each azimuth revolution of the
antenna; a synchro motor in the indicator imitates the motion of the
generator, and through a gear reduction rotates the deflection coils of
the PPI in synchronism with the antenna. Occasionally a potentiometer
or a sine-wave generator is used as the data-transmitting element. A
similar type of data transmission is required of servo-controlled scanners:
a voltage from the transmitting element is compared with a voltage from
the knob, etc., that is to control the antenna, and the antenna is automatically
driven in the direction which will bring the error signal or
difference voltage to zero.
9.12. Examples of Mechanical Scanners.-The above generalities
will be made more concrete in the description of a few specific scanners.
These are chosen to illustrate a variety of purposes, shapes, and sizes.
The SCR-584.—The antenna mount of the SCR-584 (Fig. 9.13) has
been cited as a Palmer scanner, inasmuch as it combines helical with
conical scan. The prime function of this radar,2 located in a trailer, is
to locate enemy aircraft and to provide an antiaircraft director with data
on slant range, azimuth, and elevation angle of aircraft. The beam (at
the 10-cm band, about 4° wide) is formed by a 6-ft stamped paraboloid
illuminated by an electrically offset dipole. This 120-lb reflector is
perforated with 6400 half-inch holes to reduce weight and windage. A
gear train in the base actuates the searching in azimuth at 6 rpm. A
similar gear train is located behind the reflector and actuates the elevation
motion; the excursion in elevation is covered once per minute. To
enable tracking, the electrically asymmetrical dipole feed spins at 1800
rpm, thus scanning the beam conically; this has the incidental effect of
gyrating the plane of polarization of the energy. Five units, driven by a
spring-loaded gear train, are provided for azimuth data transmission:
four synchros, of which one is geared to rotate at 16-speed, and one
potentiometer. As is common practice in data transmission, each takeoff
may be individually adjusted by loosening its mounting clamps and
rotating the stator case for proper angular setting in relation to the
antenna. After the eventual removal of the SCR-584 radar to a new site,
any necessary reorientation of the take-offs may be effected by an
ingenious ‘‘ group adjustment” of the data gear train. Units analogous
to all but one of the azimuth synchros are geared to the elevation mechanism.
The phase of the conical scan is continuously signaled by means
I Potentiometers and synchros are discussed in Chaps. 8 and 10 of Components
Handbook, Vol. 17 of this series.
* War Department Technical Manual TM-1524.