Radar System Engineering

492 THE RECEIVING SYSTEM—INDICATORS [SEC. 13.6
asecond servomechanism acting at “single speed. ” Some sort of switch,
such as a gas-filled tube, serves to transfer control to the single-speed unit
when the error becomes large enough to confuse the higher-speed servo.
For further information on the extensive subject of electromechanical
repeaters, the reader is referred to Vol. 21 of this series.
BASIC ELECTRICAL
CIRCUITS
The technique of producing radar displays involves the use of many
unfamiliar or entirely new types of vacuum-tube circuits. A great many
of these use a tube as a nonlinear element in such devices as electronic
switches, pulse formers, generators of rectangular and other waveforms,
etc. The following sections will describe briefly some of these techniques
in order to provide a basis for ‘understanding the methods of display
production.
13.6. Amp~ers.-X’o attempt will be made here to describe the
standard forms of amplifier met with in ordinary vacuum-tube circuit
E,. -L?E.ut
Adding 4
- cwcuit -
Amphfier
E,n gain=l gem=Go
+
-B Ec,u,
R=R+,
*4
R,
R2
QAmphfier
Elm
R,
–B EM E
Load 0“’
R2
FIG. 13.10.—Negative feedback principle.
practice, but a number of special
forms important in indicator design
will be touched upon. 1 The
important case of video amplifiers
has already been met in Sec. 126.
Negative Feedback.—In a large
number of instances negative feedback
is necessary to insure linearity
and adequate frequency
response. The principles involved
are illustrated in the upper diagram
of Fig. 13.10. By any of
several methods a fraction j3of the
output signal is subtracted from
the input signal ahead of the
amdifier. The effective signal to
the amplifier is then given by Eim — BE.,. The Output Sbwal Cm be
expressed as
Eou, = (Eir, –
&%t)Go,
where GOis the gain of the amplifier proper, in the absence of feedback.
Solving for E..,,
i For a complete discussion of amplifiers see Vol. 18 of thie eeriea.