TM 11-5895-1090-34/TO 31 R2-2TSC-152
d.
electric power monitor A7 (para 2-12) via variable
Diodes CR1 and CR2 are transient sup-
attenuator AT1. The level of the sampled output power
pressors. When SHF MONITOR switch S1 is placed in
fed to the thermoelectric power monitor is controlled by
the X10 position, diode CR1 applies +30 vdc to relay K1
AT1, which is a manually adjustable attenuator. The
on the transient suppressor board and diode CR2
main signal path output of directional coupler DC2 is fed
applies +30 vdc to relay K1 on the transient suppressor
through output filter FL1 to front panel SHF OUTPUT
board and diode CR2 applies +30 vdc to the common
connector J5 via cable assembly W2. The filter is a
terminal of channel select switch S3.
bandpass type which reduces both harmonics and
e. Relay K1 applies a short circuit between
receive-band noise.
terminals G and J of thermoelectric power monitor
assembly A7 when energized. The relay is energized
2-12.
Thermoelectric Power Monitor Assembly
when SHF MONITOR switch SI is placed in the X10
A7
position.
2-10.
Rf Low Power Alarm Assembly A5
Thermoelectric power monitor assembly A7 consists of
an integrated circuit thin-film thermoelectric (tft)
element, thermistor RT1, a filter, and an amplifier.
Rf low power alarm assembly A5 comprises two
Power to be monitored is selected by coaxial switch
comparators in U1 which have an adjustable threshold
A1S1 and can be from any of the four shf channels
set by potentiometer R3 on transient suppressor
(CH1-CH4) or shf output power. The coaxial switch is
assembly A4. The comparators also receive inputs from
controlled by the front panel channel select switch. Rf
diode detectors in shf drive assembly A2 and shf output
power to be monitored is absorbed by the thin-film
assembly A6. If the shf output level drops below the
thermoelectric element, producing a temperature rise in
level preset by A4R3, the output at pin 1 of comparator
the element.
This results in a thermoelectric
U1 goes positive, causing NPN transistor switch Q1 to
electromotive force (emf), proportional to the
turn on. This in turn energizes relay K1, causing the
temperature rise.
Thermistor RT1 keeps the
front panel FAULT lamp to light. If the shf input level
temperature rise in the thin-film thermoelectric small.
drops below the preset level, the output at pin 8 of com-
By so doing, the tft element acts as a true square-law
parator U1 goes positive, causing NPN transistor switch
(rms) device, producing a dc voltage directly
Q1 to turn on. This in turn energizes relay K2, thereby
proportional to the absorbed power. The dc voltage is
inhibiting the front panel FAULT lamp when rf drive is
applied through a filter (L1, L2, C1, C2) to an amplifier
not adequate. A truth table describing the status of the
which produces a constant voltage output to SHF
FAULT lamp is presented below:
MONITOR meter that is linearly proportional to the
Condition
Fault Lamp
incidental rf power. The SHF MONITOR meter has full-
scale markings of 15 milliwatts and 11.8 dbm. Three
power ranges (X10, X1, and XO.1) are selected by SHF
RF In + RD Out
OFF
MONITOR switch S1. The switch also has a CAL
RF In + Low
(calibrate) position which permits zeroing of the SHF
RF Out
ON
MONITOR meter by adjustment of CAL ZERO
No RF In
OFF
potentiometer R1. Full scale calibration of the SHF
2-11.
Shf Output Assembly A6
MONITOR meter for each channel is set by introducing
an external power-measuring standard and adjusting the
appropriate AT2 channel attenuator.
The SHF
MONITOR meter is calibrated to give accurate
Shf output assembly A6 consists of isolator HY1,
indication of power at front panel SHF CHANNEL
directional couplers DC1 and DC2, diode detector CRI,
COMBINER CH1--CH4 INPUT connectors when the
variable attenuator AT1, and output filter FLI. The
respective LEVEL ADJUST controls are set for
amplified shf signal from twt amplifier assembly A3 is
maximum level (minimum attenuation).
SHF
passed through isolator HY1 to a 10-db directional
MONITOR indication of output power is calibrated at
coupler (DC1) which samples the shf output signal.
SHF OUTPUT connector J5 by use of an external power
Diode detector CR1 detects this signal and provides an
monitor standard and adjustment of variable attenuator
output to rf low power alarm assembly A5 (para 2-10)
A6AT1.
that is proportional to the level of the shf output. The
main signal path output of directional coupler DCI is
applied to a second 10-db directional coupler (DC2)
which provides a sample of the shf output to thermo
2-5
