Radar System Engineering

SEC. 17.6] THE PHASE-SHIF.T METHOD 699
Video
Trigger
From
receiver
{ t
Switch (b’)
Switch .M’ Flip-flop
and
(d)
(d)
decoder
f
I’
t
,
Flip-flop
Flip-flop
,- Delay E
(a)
: “-1 - ‘b’) =
A’ I
F’ I
k
Switch — Comparison
(c)
circuit
. 4
,~G’
Amplifier
Switched Switch D’ Pulse c’ Phase
.
oscillator (a’) former shifter
~B’
#
,
I
I
I
Waveforms
~u,,e
_ Pulse train —
A;~ C;#E:G’ Same as A,B, C, etc. except later
in time by width of code
F’
M’
Trigger
FIG. 17.8b.—Pheee-shifted pulses, receiving station.
I
The method is illustrated in Fig. 17.8. At the transmitter the master
pulse triggers a square-wave generator (flip-flop a) which switches a
shock-excited oscillator (Fig. 13.41). The oscillation B is passed through
a phase shifter geared to the scanner, and the resulting wave C produces a
pulse train D.
In order to avoid early transients which might lead to confusion with
the master pulse (especially after coding) the first two or three pulses in
the train are excluded by switch a. This switch is controlled by a square
wave from flip-flop b; it is arranged to turn on late enough to exclude the
required number of pulses and to remain on until after the end of the pulse