Radar System Engineering

498 THE RECEIVING SYSTEA{—IA’DICA TORS [SEC. 137
Grid gl now rises, until at t, it reaches cutoff and regeneration occurs in
the reverse direction, and so on. Thus two square waves of opposite
phase are available from the two plates. For given tube types and
supply potentials, the time interval tl – tz is primarily determined by
RZCZ, and the time interval tz- t,’ by RICI; these furnish convenient
constants by means of which control of the time intervals can be exerted. I
The multivibrator can be used as a completely free oscillator, or it can be
synchronized by supplying it with a sine wave or a pulse train at a higher
frequency than that of the natural oscillation.
Figure 13.14 shows a single-stroke or “flip-flop” multivibrator.
The resistors and the bias voltage of the grid of V, are so chosen that
when VI is fully conducting, gj comes to equilibrium beyond cutoff; but
when VI is cut off, g~ is pulled hard against the cathode. If left to its
“B +c2=25//Lf
+ c,
R, 400 k
---
Trigger ‘--
v, 100 k ~
-lCOV
&
(1) Trigger ~
(2) Gnd 1
‘3) “a’el _rLnrL’+
“)p’ate’U1-rL-r’+
FIO. 13.14 .—Eccles-Jordan Sip-flop.
own devices, the circuit will come to equilibrium with VI on and Vj off.
When an impulse of the correct polarity is applied to g, or to g,, the
regenerative action cuts off VI and turns V2 full on. Grid gl then rises
until the cutoff point is reached, when the regeneration reverses and the
cycle is completed with the original condition restored. The length of
the square pulse during the flip-flop action can be easily controlled by
varying RIC1 or the potential applied to RI. This voltage is made positive
to assure that gl will be rising sharply when the cutoff point is
reached; this helps maintain-a constant square-wave duration. Typical
circuit constants are indicated in the grid circuit of V2. The condenser
Cz serves only to quicken the regenerative action and is not essential
except for the highest speed operation.
The “ flopover” and the “scale-of-two” (Fig. 1315) are direckoupled
in both directions in such a way as to have two stable states, and will
remain in either until disturbed in the proper manner. In the flopover,
1For simplicity it can be assumed,as is practically always the case, that the supply
voltage is much higher than the cutoff voltage and that the plate re&tors are much
smaller than the grid resistursbut large enough to abeorb most of the potential drop
when in serieswith a saturatedtube.