Radar System Engineering

378 THE MAGNETRON AND THE PULSER [SEC. 10.10
the same material. The tube is filled to a pressure of a little less than one
atmosphere with a mixture of 75 per cent hydrogen and 25 per cent argon.
Two or three tubes are used in series, with a voltage divider across them
to ensure that the network voltage is divided equally among all the gaps
before the pulse takes place. Triggering is accomplished as shown in
Fig. 10.39 by depressing or raising quickly the voltage of the two middle
electrodes. This breaks down one of the gaps and throws full voltage
across the second gap. The overvolted second gap thereupon also
breaks down, forming a low-impedance path between points A and A‘.
These switches are efficient and are quite satisfactory in use. Their chief
limitations are in the allowable pulse repetition frequency (about 2000
DDSmaximum) . .
and in obtainable precision of pulse timing. This type
of switch can handle several megawatts,
and should be useful in applications
that do not require great
flexibility or accuracy of firing.
A particularly successful version
of the series-gap switch is the Bell
R T e 1e p h o n e Laboratories’ 1B42,
which substitutes a mercury-saturated
iron “sponge” for the solid
aluminum cathode of the 1B22. By
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Trigger input
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II
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FIG. 10.39.—Series gaps.
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Voltage
dwider
(r
‘t
Triggerinput
FIG.
10 40. —Trigatron.
using an atmosphere of relativel y high-pressure hydrogen, the temperature
variation of mercury vapor pressure is made unimportant. Since the
ordinary series. gap is limited in operation by pitting and spike growth,
the mercury cathode provides better operation over a wide range of