Radar System Engineering

SEC. 13.9] ELECTRONIC SWITCHES 509
pulses occurring during a given time interval. The triode can be used
ouly if both signals are limited, since otherwise it could be turned on by
n ‘I-#
~ndb%
cutoff ‘–-–
---
::-
,“,off -* ‘;A,,,C,
n(a)
+
4
(b)
cutoff
n
~ndA
cutoff–--–
---
L-1
----- “s’
Signal
*
(c)
cutoff e
Gnd ‘--– n
+
14 !4
(d)
---
---
---
6’c7etc.
Fm. 13.27.—Gated amplifiers. (a) Switched triode; (b) multicontrol tube switched on
second control grid; (c) suppressor switching; (@ screen switching.
one alone. The circuits of diagrams(b) and (c) of Fig. 13.27 require the
least power input. The 6AS6, which has a sharp suppressor cutoff, is
the most satisfactory tube unless considerable load current is needed.
Since none of the tubes that can
deliver laTge currents has either a
second control electrode or a sharp
suppressor cutoff, it is customary to
use screen gating when the current
requirements are high. In the case of
+S!gnals
video signals, the tube must have a from
very sharp cut off on the signal grid; source1
even then it is usually necessary to
choose between an extreme bias, which
FIG. 13.2 S. —Switching of alternate
sacrifices gain at low signal amplitudes.
and a lesser one. which allows a
signals.
“ plateau” to be transmitted. The use of two tubes in the way described
in the next paragraph is more satisfactory.
Two such switches can be used in parallel to alternate signals from
two sources, as shown in Fig. 13”28. In thk case the simultaneous but
opposite switching of the two tubes eliminates the plateau if the two cir-