(4) Tune the second cavity and then the
1-55.
STAGGER TUNING METHODS
output cavity for maximum power output. In the
case of a five-cavity klystron, this step would
We will discuss two methods of stagger
instruct you to tune the second, third, and output
tuning a klystron. To keep things straight, we will
cavity (in that exact order) for maximum power
call them METHOD 1 and METHOD 2. Both
output.
methods require pretuning the klystron by the
synchronous method, then stagger tuning.
In
(5) This step is the most critical.
METHOD 1, you have to readjust the penultimate
Slowly tune the last (penultimate) cavity (in this
cavity and the input RF drive. METHOD 2 requires
case, the third cavity) toward a lower frequency until
a rapid-sweep RF driver or exciter.
the output power reaches maximum and then
decreases slightly. Return the tuning to the point of
1-56.
METHOD 1, STAGGER TUNING
maximum power and then detune to the high
frequency side until the output power drops slightly
a. Tune the klystron by the synchronous
below maximum.
DO NOT OPERATE
method (para 22).
PENULTIMATE
CAVITY
AT
LOW
FREQUENCY SIDE OF MAXIMUM POWER
b. The first step is to increase the RF input
POINT. Figure 58 shows the correct tuning point
power until the tube is operating at saturation.
for the penultimate cavity.
c. The second step is to detune the
(6) After the cavities are tuned decrease
penultimate cavity in the higher-frequency direction.
the drive to a low value, then increase the drive to a
Detuning should be continued until the output power
point where increased drive no longer results in
drops approximately 1/4 to 1/10 of maximum. As
increased output power. Then reduce the drive
you detune the penultimate cavity, the output power
slightly to the point where output power just begins
will decrease, because more input power is needed
to decrease. This is the stable operating point. For
for saturation.
stable operation, drive power should be no more
than necessary. Excess drive will cause saturation
d. The next step is to increase the RF input
and decrease in power output as well as excess
power until the tube is, again, operating at
current in the cavities.
saturation. You will find that this "new" saturation
power output is higher than the power output which
you were able to obtain with the tube
synchronously-tuned. You may be able to "squeeze
a little more out" of the tube, but probably not much.
You can detune the penultimate cavity still further
and then increase the drive to see if you get more
power output than you had before. The maximum
power output is normally quite broad; you will find
that you can detune the penultimate cavity
considerably around either side of this point without
making an appreciable change in the saturation
power output. Eventually, the extent to which you
can increase the output power will become limited
by the available power from the exciter.
1-57.
METHOD 2, STAGGER TUNING
Stagger tuning by sweeping the frequency
PENULTIMATE CAVITY FREQUENCY
of the RF driver achieves the broadest
Figure 58. Penultimate cavity tuning.
bandwidth characteristics over the passband.
However, the details of broad-band tuning
which you may be required to accomplish
344 L1
54
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