Radar System Engineering

SEC.K3.121 RANGE AND HEIGIiT INDICES; SYNCHRONIZATION 521
spaced markers desired.’ Lower-frequency markers are provided by
scaling circuits. A final scaling circuit provides pulses of proper frequency
for triggering the modulator, the sweeps, etc. In the figure it is assumed
that the desired frequency values are successively integral multiples of
the lowest frequent y. If this is not the case, multiple counting channels
are necessary; for simplicity an integral relationship is usually chosen.
When synchronization is external, the oscillator must be shockexcited.
Figure 13.38 illustrates an LC-oscillator widely used in mediumprecision
applications. When VI is conducting, the circuit is quiescent
and energy is stored in the inductance by virtue of the cathode current.
~ Scaling ~ Scaling
Oscillator : Amplifier L :::.;’;.: circuit T circuit
-nl
T nz
I I
I ~-xkw
a. Sinusoid
b
Square wave
c. l-mile marks I I I I I I I I I I I I 1 [ I
c. l-mile marks
(compressed scale) ~11111 — .—— —.— ___ ___
Iulllulllllll
d. 5.mile marks 11111111111111111111 [11111111 11111
e. 20.mile m~ks I I I I I 1 I 1
f Trigger I I
FIG. 13 37,—Derivation of pulses from c-w oscillator.
Interruption of this current by the square wave shock-excites the oscillating
circuit. The resulting voltage wave has an initial phase of zero
and an approximate amplitude of 1-. The constants of the
Hartley circuit of Vj are so chosen that this initial amplitude is just
preserved. In the present example the amplification necessary to produce
steep wave fronts is provided by the regenerative amplifier formed
by VS, V,. Each time that V, is turned on, the surge of current through
its plate circuitz triggers the single-stroke blocking oscillator formed by
V5, giving rise to the desired pulse. It should be noted that a slight
delay is inherent in the production of the first pulse, since a short but
finite time is required to turn on Vq. Later pulses are all displaced by
1For example, in the case of 1-mile markers this frequency is 93.12kc/see.
* The current necessary to charge C? increasesthe positiveness of this action.