TM11 -6625 -2948 -14+P
NOTE
In order to produce oscillation over the frequency range of
the oscillator, a tracking arrangement is used to vary the dc
The
F control (1A3R28) provides a small
voltage on the repeller so that it is maintained at the
variation in the repeller voltage, which pro-
optimum value for a given plunger setting
duces a vernier frequency variation of at
least 1.5 MHz.
At a certain frequency value (8.15 GHz), the repeller volt-
age becomes excessively high and it is more practical to
Protective diode (A3A1CR4) is connected between the
change the repeller voltage to a new range. This can be done
cathode and repeller of klystron (1V1) to prevent the
without changing the frequency of the oscillation at a given
repeller from becoming more positive than the cathode
cavity setting by lowering the repeller voltage so that the
which would damage the klystron.
tube operates in a higher mode. In the higher mode the
bunched electrons require a longer time in cycles to be
returned to the resonator grids. It operates in the 2% and
4% modes. The switching arrangement is described in
The frequency control knob rotates the shaft which drives
the digital readout, the cam that positions the tuning
probes; the attenuator probe with a variable amount of
plunger, and the tracking potentiometer, each through the
insertion that determines the rf power level delivered to
appropriate gearing. The shaft extends through the tuning
the RF OUTPUT connector, and the fixed rf monitor probe
mechanism casting to the rear of the instrument where it
that supplies the power sample for automatic frequency
can be attached to an external motor drive, if required.
stabilization. Model SG-1145/URM incorporates a third
power monitor probe, with a variable amount of insertion,
that supplies power to the monitoring circuit for calibrating
the output attenuator.
Power from the klystron cavity is coupled through two
symmetrical pipes into two matched waveguide-beyond-
cutoff attenuators. The POWER SET control positions the
power set probe in its pipe. The power set probe couples
rf power from the klystron cavity to the crystal detector
The dc voltage applied to the repeller is controlled by track-
ing potentiometer (1A7R1). The movement of the arm
and the power monitor meter and also moves the hairline
of the attenuator dial. When the POWER SET control is
of 1A7R1 is mechanically ganged with the movement of
adjusted for a power monitor meter indication of CAL, the
the tuning plunger in the klystron cavity so that the repeller
voltage is maintained at the optimum value for the maxi-
power set probe is coupled to approximately 1 milliwatt
mum amplitude of oscillation. Repeller mode switch 1A7S1
power level. Should the energy level within the cavity
is operated by a cam driven by the tuning drive and changes
change when the cavity is tuned to a different frequency,
the power set probe must be reset to obtain the 1 milliwatt
the voltage applied to 1A7R1 so that a different mode can
level of power absorption which will bring the power
be used. The values of the resistors in the tracking circuit
monitor meter back to its reference CAL position. At the
are calculated for the proper frequency-vs-voltage character-
same time, the hairline is repositioned to a new 0 dBm
istic. Adjustment potentiometers are provided in the
reference. When the POWER SET adjustment is set for
t r a c k i n g circuit to compensate for variation in klystron
CAL, the attenuator probe is adjusted for 0 dBm output
repeller voltage characteristics. The maximum voltage
at the same time that the attenuator dial is adjusted for
across tracking potentiometer 1A7R1 is 600 v, since it is
0
dBm
under
the
hairline.
In
this
way,
as
frequency
is
connected from the -1250 volt beam supply to the -1850
varied, and the power monitor meter is set for CAL by
volt repeller supply. The cathode of klystron 1V1 is con-
placing the attenuator dial at 0 dBm under the hairline,
nected to the -1250 volt beam supply and therefore the
the output will be 0 dBm within the specification accuracy.
repeller voltage can vary from 0 to -600 volts.