Radar System Engineering

SEC. 108] LOAD REQUIREMENTS 363
TABLE 103. -CO~PARISON OF THE Two PULSER TI-PES
Characteristics
Hard-tube pulser
Line-type plllser
Efficiency
Pulse shape
Impedance-matching
Interpuke interval
Voltage supply
Change of pulse duration
Time jitter
Cmcuit complexity
Effects of change in
voltage
Iwwer; more overhead power
required for driver, cathode
heating, and for dissipation
in switch tube
Better rectangular pulses
l~ide range of mismatch permissible
lIay be \-cryshort, as for coding
beacons (i.e., < 1 psec)
High-voltage
necessary
supply usually
Easy; switching in low-voltage
circuit
Somewhat easier to obtain High-power
negligible time jitter, i.e.,
< 0.02 /see, than with linetype
pulscr
Greater, leading to greater
difficulty in servicing
For design ha}-k g maximum
et%ciency, (AP/P) output =
6(AV/\’) input. By sacrificing
efficiency in the design,
(AP/P) output = 05 (AV/~)
input can be obtained
High, particularly rrben pUkepower
output is high
Poorer rectangular pulse, particularly
through pulse transformer
Smallerrange of mismatch permissible
( + 20-30 per cent).
Pulse transformer ~vill match
any load, but power input to
nonlinear load cannot be
varied over a wide range
X[ust be several times the
deionization time of discharge
tube (i.e., > 100 psec)
Low-voltage supply, particularly
with inductance charging
Requires high-voltage switching
of network
line-type pulsers
with rotary-gap switch have
inherently large time jitter.
With care in design and use
of hydrogen thyratron or
mercury-sponge type of enclosed
gaps, time jltter of
0.02 usecor less obtainable
Less, permitting smaller size
and weight
Better than a hard-tube palser
designed for maximum efficiency
since (AP/P) output
= 2(AV/v) input for linetype
pulser, independent of
design
load may also display occasional short-circuit and open-circuit conditions
which must be allowed for in the pulser design.
Confining our attention to the magnetron, we note in Fig. 10.29 that
it displays a dynamic impedance at the operating point of only 430 ohms,
even though the V-1 impedance ratio is 1480 ohms there. Both the
operating and the dynamic or incremental impedance are important; the
former determines the rate at \vhich po\ver will be absorbed from the