Radar System Engineering

524 THE RECEIVING SYSTEM—INDICATORS [SEC. 13.13
as illustrated by the dotted part of Fig. 13.40. It is quite feasible to
provide discrete indices on the expanded sweep by providing pulses of
sufficiently high frequency to be useful. These may, for example, arise
from anearlier stage of thechain of Fig. 1337thant hatwhichprovides
the delaying trigger pulses. Such multiple-scale systems are described
in Chap. 6 of Vol. 20 of the series.
DISPLAY
SYNTHESIS
Displays are synthesized by combining the components and techniques
described in the preceding sections of this chapter. Although space
will permit only brief descriptions of some of the more important and
~haracteristic of the methods used, variations to fit particular circumstances
and extensions to other applications will be apparent in many
cases.
13.13. The Design of A-scopes.—This section will describe two
methods for synthesizing type A displays, one of extreme simplicity
intended only for test and monitoring purposes, and the other of a more
elegant
form.
A Simple A-scope.—In Fig. 13.41 simplicity of design has been carried
to the extreme in producing an indicator intended only for testing or
monitoring applications in which brightness and sweep linearity are not
of great importance. The operation of the circuits is as follows. Tube
Vla and the first three elements of Vz form a flip-flop providing a square
wave, A, for intensifying the cathode-ray tube and at the same time
cutting off the current from the plate of Vz, on which a positive sawtooth
is formed by the usual condenser charging circuit. One of the horizontal
deflecting plates of the CRT is driven directly by this sawtooth; the other,
by a negative sawtooth provided by the inverting amplifier V1~, which
is provided with cathode feedback. Since a rather large sawtooth
( = 100 volts) is generated without exponential correction, the sweep
slows down slightly toward the end.
As is shown, two sweep speeds are provided, one of 300 psec using C,
as the integrating condenser, and a second of approximately 5 psec using
the stray capacity at point 1?. More values can of course be provided
by adding more switch points and condensers. In the interest of simplicity
the flip-flop is not switched, being left on for the duration of the
slower sweep. When the faster sweep is used, the beam is swept entirely
off the tube face and remains off until termination of the flip-flop.
The video amplifier illustrated has a bandwidth of about 1 Me/see,
the exact value depending upon the stray capacity introduced by the
connecting circuits.
The power supply should include a conventional rectifier and LC-filter
to provide the 300 volts direct current and an W’-fdtered negative supplv