TM 11-5895-846-14
(2) An isolated output from the input
fault sensing, equipment safety, and control. Most of its
directional coupler is detected and sent to the RF alarm
circuitry is in the form of removable modules.
module for use in monitoring and fault detection circuitry.
This signal inhibits RF amplifier fault indications in the
In operation, three-phase, 120/208 Vac primary power is
absence of an input signal. Three separate low-level
supplied to the line rectifier and filter from the power
outputs from the output directional coupler are used to
distribution panel. The START and BLOWER circuit
measure output RF power and reflected power from the
breakers apply ac line voltage to the fans and start
antenna transmission line and to provide a low-level
module. When these are on, the power supply start
signal to the test translator for use in loop testing. The
cycle begins. A resistor in series with the filter capacitors
forward or out-put RF signal output from the coupler is
limits the turn-on line surge current to less than the
also used in a low-power RF alarm network which warns
required operating current. Rectified line voltage is
an operator of a reduction in amplifier output power
applied to the low voltage, control and overload, pulse
below a preset level. The klystron is cooled by a three-
synthesizer, and HV overload modules.
The start
phase, ac, squirrel-cage blower mounted inside the RF
module supplies control voltages which power several of
amplifier. Heat sensors at the klystron and the RF load
the other modules. The pulse synthesizer module
(Z1) inhibit application of high voltage to the klystron if
provides the drive outputs for the low-voltage and all of
either of these units overheats.
the high-voltage switching modules. For an initial period
(3) The front panel of the PA provides all the
of one second, all drive outputs are inhibited to allow the
drawer's controls and indicators, which include the
pulse synthesizer to stabilize. After the one second
OUTPUT LEVEL adjustment knob, the elapsed-time
delay, the inhibit is removed from the circuits providing
meter (FIL HRS) for the klystron's filament hours, the
drive to the low-voltage module. A switching section of
LOW OUTPUT ALARM SET knob, the meter ZERO SET
the low-voltage module drives the filament module,
adjustment, and the meter select switch.
which produces the klystron filament potential. To
(4) The RF amplifier and high-voltage power
prevent a large surge current from being drawn by the
supply are separate units, but are not capable of
cold filament, a primary surge limiting resistor is used.
independent operation without special load terminations
After a period of thirty seconds, a filament surge timer
and power sources. Both contain monitoring networks to
circuit on the low-voltage module activates a filament
enable fault isolation to a replaceable module, but some
surge bypass relay and allows full filament voltage to be
RF amplifier fault isolation is done at the high-voltage
applied to the klystron.
A potentiometer allows
power supply. However, a 15-volt power supply for the
adjustment of the filament voltage. At this point, all of
the power supply circuits are active except the high
RF power monitor, output power, reflected power, and
voltage section, which is inhibited by a filament time-
tube operation can be monitored. Problems in the high-
delay circuit in the pulse synthesizer. After a four minute
power output network or transmission line to the antenna
period, during which the klystron filament is permitted to
that cause high reflected energy will cause a fault alarm.
reach the proper operating temperature, the filament
A disconnected waveguide coupler will inhibit the
timer removes the inhibit from the high-voltage drive
operation of the klystron. If RF power falls below a level
circuits, and the high-voltage switching modules are
set by the LOW OUTPUT ALARM SET, a fault will be
activated. To prevent a high transistor surge current
indicated by a front panel FAULT indicator. Other
from occurring during initial high voltage turn-on, a surge
problems associated with the power supplied to the
limiting resistor, in series with the high voltage capacitor,
klystron, such as klystron arcing, are checked at the
is used. Two hundred milliseconds after a high-voltage
high-voltage power supply.
turn on, a vacuum relay is activated to short-circuit the
g. High Voltage Power Supply. The high-voltage
turn-on surge-limiting resistor.
power supply contains the circuitry necessary to convert
line power to the power required by the klystron. It also
supplies the cooling fan power and provides circuitry for
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