TM 9-4931-294-15/2
When the signal source is unleveled, the difference
frequency doubler V5. The 25MHz nominal reference
amplifier senses the difference between the reference
signal from amplifier V8 is applied to one side of the
level established by R102 and a sample of the anode
phase detector.
The nominal 50MHz output from
voltage. During sweep operation, a blanking pulse is
frequency doubler V5 is applied through frequency
also applied to the difference amplifier. The blanking
doublers V6 and V7 to generate the nominal 200MHz
pulses are synchronized with the sweep frequency and
signal with nominal 100MHz sidebands. This output and
serve to remove the anode voltage from the BWO tube
the 20MHz signal applied from frequency doubler V3 is
during the 10millisecond period between sweeps.
(b) When SQUARE WAVE SELECTOR switch
c. The nominal 200MHz signal is multiplied in the
varactor harmonic generator and produces harmonics in
S105 is in the ON position, square wave generator Q203,
the frequency range from 1 to 18 GHz. The nominal
Q204 and Q208 is energized and its output is also
100MHz and 20MHz sideband signals are also applied to
applied to the difference amplifier, superimposing the
square wave on the anode voltage. The output of
so that mixing occurs. This produces a spectrum of
difference amplifier Q201 is applied through emitter
harmonics nominally 100 MHz apart in the frequency
follower Q207 to dc amplifier Q206. The output of
range from 1 GHz to above 18 GHz and additional
amplifier Q206 is applied to the base of pass transistor
harmonics 20 MHz apart in the frequency range from 1
Q205, thereby controlling the output voltage of the anode
to 8 GHz. These harmonics are applied to the mixer
supply. Zener diode VR204 and resistor R214 provide a
(located in the respective rf heads for the Kand Abands).
potential of +130 volts dc for operation of the constant
d. The phaselock output signal from the auxiliary arm
current load.
of the directional coupler in the rf head is also applied to
the mixer. This signal is a sample of the rf output from
2-9. Tunable Synchronizer
the rf head. The mixer generates additional harmonics
a. Frequency stability to 1 part in 10' in the CW mode
from the signals applied from varactor harmonic
of operation is obtained by the tunable synchronizer
(figure 215). Basically, the rf output frequency of the
phaselock signal to obtain an IF signal that is
signal source is phaselocked to a crystal reference, thus
approximately 25 MHz. This IF signal is applied to the
obtaining a microwave source with crystal stability. The
25MHz amplifier located in the 25MHz IF unit. The
reference crystal selected is one of 16 crystals used to
25MHz amplifier has five stages and a gain of
provide continuous coverage from 0.5 to 40 GHz. These
approximately 100 db over a bandwidth of 3 MHz. The
crystal oscillators are temperature stabilized in an oven
level meter signal is obtained from the output of the third
to minimize residual frequency modulation and frequency
amplifier stage. The SIGNAL LEVEL control varies the
drift. The lowest crystal frequency is 4978.125 kHz and
gain of the second stage to obtain an output level from
the highest is 5025.000 kHz. One of these 16 crystal
the 25MHz IF unit which is the same as the nominal
25MHz reference level applied to the phase detector.
This output is applied to the phase detector which
compares the phase of the amplified signal to the
b. The input to the frequency multiplier chain is
reference signal for an indication on the phase meter.
amplified by tuned 5MHz amplifier V1, applied through
The LOCK RANGE control, which can vary the output
amplifier frequency doubler V2 to frequency doubler V3
voltage by +50 volts, is adjusted for a zero phase
and frequency x 5 multiplier V4. The 20MHz nominal
indication, which sets the drift correction voltage to the
sideband frequency output of frequency doubler VS is
desired level. This drift correction voltage is combined
applied to the output of frequency doubler V7. The
with the helix
25MHz nominal output of frequency x 5 multiplier V4 is
applied to 25MHz isolation amplifier V8 and to
2-18