Radar System Engineering

SEC. 13.7] GENERATION OF RECTANGULAR WAVEFORMS 499
triggering signals from different sources, applied to the opposite sides,
result in opposite actions. Regardless of the order in which pulses are
received from the two triggering sources, the flopover will respond alternately
to triggers from the two.
ahc /
+
r-----l
Trigger
i
ac
Trigger1
Ḷ
(a)
FIG. 13.15.—Double external triggering of Eccles-Jordan circuits. (a) Flopover; (b)
scale-o f-t wo.
In the scale-of-two, pulses from a single source are applied to both
sides; whenever a pulse arrives the circuit changes from one stable state
to the other. Thus two pulses are required to complete a full cycle.
The output waveforms can be used directly for switching purposes, or
they can serve as a means of generating pulses of half the frequency of
the original ones.
EPP
In all the above circuits it is feasible to use
self-biasing, but care must be taken that the
bias voltage is independent of duty ratio.
c
This can be assured by using a common selfbias
resistor for both tubes, provided their
--- ---
loads are the same.
&
Cathode-coupled Multivibrator.—F i g u r e V
13.16 illustrates a different type of single- Irk
stroke multivibrator which is considerably
R
= .
better than the Eccles-Jordan variety for FIG. 13. 16.—Cathode-coupled
Sip-flop circuit.
accurate timing purposes. The two cathodes
are coupled through a common resistor, and plate-grid coupling is used
in one direction only. In the normal state, Vz is conducting by virtue
of the positive grid supply voltage. The resulting current produces
sufficient potential drop across Rk to cut off V1. If, now, a positive
trigger pulse of sufficient voltage is applied to gl (or a negative pulse to g,)
the amplified pulse is applied to Vz through C, and V2 starts to cut ofi.
Ḷ
(b)