TM 11-5820-921-40-1
2-112. Inductor 1Al0L2 is
used to
compensate for the
phase delay through transformer
1A10T1. In
addition, inductor 1A10L2 is used as a high frequency adjustment to vary the phase of the voltage
developed across resistor 1A10R15 for zero balancing. Inductor 1A10L1 is the mid-frequency balance
control for the phase detector, while inductor 1A10L3 is the low frequency balance control for the
input (CATHODE) voltage sampling network and has a slight affect on the phase at low frequencies.
Inductor 1A10L1 has its greatest effect at 8 MHz due to the resonance of the all-pass network. Resistors
1Al0R6 and R8 are used to compensate diode detectors 1A10CR2 and CR3, making the detectors less
2-114. Subsequent paragraphs 2-115 through 2-124 describe the tune cycle control.
2-115. In the preceding
paragraphs, the
functioning of the
individual elements of the
servo system under
various control and command signal conditions was described. The operation of these elements
(e.g., ON-OFF switching, sequencing, interlocking) is controlled by the high level discrete component
logic circuits on Tune Control PWB Assembly 1A4, which also provides and accepts system interface
signaling to and from the receiver-transmitter and the antenna coupler. Table 2-5 will help in
understanding how the tune cycle control functions.
2-117. The tune cycle is initiated by a 30 millisecond ground pulse (TUNE START) on pin 16, of Tune
Control PWB Assembly 1A4, whenever the receiver-transmitter operating frequency is changed or the
system dc power is switched ON. The ground pulse on pin 16 (TUNE START) momentarily switches ON
the tune latch circuit (P/O 1A4U1 and 1A4U2) and the tune time latch circuit (P/O 1A4U6). The tune
latch circuit and the tune time latch circuit are latched ON for the duration of the Tune Cycle. This
prevents normal Receive-Transmit operation until the system has been correctly tuned. When pin 13 of
1A4U1 is grounded, a logic " 1" level (high) is applied to the base of transistor 1A4Q3, turning the
transistor ON and applying a ground to the TUNE line at pin 22 of 1A4. The TUNE (ground) signal is sent
to Servo Amplifier 1A5 as the SERVO ENABLE (ground) signal to activate the servo amplifier.
The TUNE (ground) signal is also sent to ALC Module Assembly 1A7 (pin 2) to energize Tune Relay
1A7A1K2, connecting dummy load resistor 1A7A1R1 in series and resistor 1A7A1R2 in parallel with
the power amplifier rf output.
CONDITION
2-119. When pin 13 of 1A4U1 is grounded, a logic "1" (high) is applied to pin 1 of 1A4U6 producing
a +10V (high) LMAX FORCE signal that is sent to Servo Amplifier 1A5 through pin 5 of connector
1A4P1. This forces torque motor 1A8A3B1 to drive coil 1A8A5L1 toward its maximum inductance
value. When the coil has been tuned to maximum inductance, the limit switch 1A8A3S1 stops the
motor and grounds the LMAX LIMIT signal line. (Grounding the LMAX LIMIT signal line (1A4P1-18)
applies a low logic level to pins 1 and 2 of NAND gate 1A4U5. If the tune cycle was initiated by
equipment turn-on, the tuning cycle will be interrupted at this point, until the time delay (60 seconds)
in the power supply has timed out. Interrupting the tune cycle until the warm-up time delay is
completed, insures that the tubes have had sufficient warm-up time to be ready to transmit, The TUNE
START signal (ground) is also sent to the antenna coupler to initiate a similar TUNE PRESET sequence
there.
2-120. AUTOMATIC TUNE CYCLE CONTROL
2-121. The final automatic tuning of the Power Amplifier is initiated (after frequency selection and/or
the warm-up delay have been completed) by depressing momentarily the PTT key on the handset. This
applies a momentary ground on the KEYLINE signal line, pin 12 of 1A4, and pins 8 and 9 of NAND
gate 1A4U5. This in turn switches (and latches) U5, U4, U2, and U6 into saturation, shorting to ground
the LMAX FORCE command signal line. The KEYLINE ground also forward bias the gate of
unijunction transistor 1A4Q5, latching it into conduction. In System Control PWB Assembly 1A3,