Radar System Engineering

SEC. 13.9] ELECTRO.VIC ISWI TCHES 507
other hand, is satisfactory in this respect. Care must be taken in the
latter that ‘‘ droop” in the switching-off pulse does not allow the grid to
go too far positive when the clamp is closed, for this can produce overshoot
through grid-cathode diode action. Square-wave droop can also
cause overshoot in the positive clamp if the clamping is not tight.
The relative merits of the various single-sided clamps depend upon
the uses to which they are to be put, the type of switching source available,
and so on. If a proper driving source already exists, the simple
diode (Fig. 13.23a) is cheapest and best. If not, the triode of Fig. 13.24b
best combines simplicity and good characteristics among the negative
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FIG. 13.25 .—Two-waY clamps. (a) Two-way double-triode clamp; (b) two-way four-diode
clamp.
clamps, and Fig. 13.23c is the best and Fig. 13.24a is the simplest of the
positive clamps. If the load impedance is high, the latter may be quite
satisf act ory.
Two-way clamps are usually made up of two one-way units of opposite
polarities, as indicated in Fig. 1325a and b. The requirements and
shortcomings of the corresponding one-way clamps apply equally here.
The “phase splitter” of Fig. 13.12 provides an excellent driving circuit
for Fig. 13.25b if it is necessary to provide a special one. If a proper
driving source is used, the four-diode clamp can be much “tighter” than
the two triodes in the positive direction. Furthermorej the capacity
coupling through the two triodes adds, whereas in the diode circuit the
effects of the opposite waves tend to cancel. On the other hand, the
double-triode circuit is much the cheaper, particularly if a special driving
circuit must be provided for the diodes.
(b)