g. A Guillemin line is a specially-constructed, pulse-forming network.
Learning Event 4:
HYDROGEN THYRATRON SWITCH
1. The switch used to discharge the PFN is one of the most critical
components in the high-level modulator. Here are some reasons why.
a. The switch must be nonconducting (off) during the charge of the
pulse-forming network.
b. The switch must close very rapidly at the pulse repetition frequency
of the radar.
c. The switch resistance
must
be
as
small
as
possible
during
the
discharge of the PFN.
d. The switch
must be capable of
conducting high
currents without
damage.
e. Some early radar sets used spark gaps to discharge the PFN.
Figure
56 shows two common types: a fixed spark gap and a rotary spark gap.
(1) The two-electrode spark gap shown in Part A works just like the
spark plug in your car. During the charge of the PFN, the spark gap is an
open circuit. Hence, its resistance is very large. As the PFN charges, the
potential across the electrodes builds up rapidly.
When the potential is
large enough, the air between the electrodes breaks down (ionizes) and a
spark jumps across the electrodes. This makes the resistance of the spark
gap very small, and, thus, the PFN is short-circuited.
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