Radar System Engineering

SEC. 17.7] GENERAL METHODS OF RELAYING SINE AND COSINE 701
closed all signals (video and interference) are excluded until the flip-flop
returns to its stable condition shortly before the next basic pulse.
17.7. General Methods of Relaying Sine and Cosine.-A complete
description of an angle can be given by expressing its sine and its cosine
in the same units. Probably the greatest variety of actual and proposed
systems for data transmission have involved the relaying of these quantities
in one way or another.
If sine and cosine of the scan angle are transmitted, these data can be
used for ,PPI synthesis either with or without mechanical motion. Since
AC line voltage (f~
>
I A sin h fot
e
? ‘
A cos O sin 2rr fot
Oscillators
mixer
transmitter
T
w
—
Video signals
and trigger pulse
Recewer
Filters
&
[
Video signals
FIU. 17.9.—Hypothetical method of transmitting synchro data by c-w,
the method of synthesis has an important bearing on the choice of a relay
method, a brief discussion of the use of the data will be given. T\vo
general methods are possible: mechanical duplication of the scanner
motion at the receiving station (as in the previous cases), or use of the
sine and cosine voltages to produce the two necessary PP1 range-sweep
“omponents.”
Derivation of mechanical motion from sine and cosine information
requires the use of a servomechanism. Practically speaking, it is necessary,
in order to reproduce the mechanical motion, to provide a-c voltages
proportional to sine and cosine, as well as a voltage of constant amplitude
for reference purposes. .111 voltages must have the same frequency and
phase. From the terminal-equipment standpoint these voltages could
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