2-85. In the second column of AND gates, the AB logic " 1" input, at 1A6U3-8, is combined with the EF
logic "1" input, at 1A6U3-9, to produce the logic " 1" ABEF output, at 1A6U3-10. In the third column of
AND gates, the CD logic " 1" output from the first column is applied to 1A6U5-8 and combined with the
ABEF logic" 1" input, at 1A6U5-9, to produce the logic " 1" ABCDEF output, at 1A6U5-10. This biases
transistor 1 A6Q7 ON, applying ground to diode 1C6CR 11, which lights indicator 1A6DS7 to show that
BAND A is selected, and applies a ground on the BAND CODE A signal line, which corresponds to position
3 on band control selector switch wafer 1A8A4S 1-A. The preprogrammed bandswitching is completed in
less than one second after a frequency code signal change is received from the receiver-transmitter. The
eight band positions on band control selector switch 1A8S1 are not in an increasing frequency sequence.
The positions have been arranged to allow the shunt components of higher frequency bands to be connected
between the proper switch wafer contacts and ground with the shortest possible lead lengths (to minimize
lead inductances). In the lower frequency bands, lead inductance is not critical, because of the relatively
high inductance setting of coil 1A8A5L1 when the pi - network is tuned.
2-87. The BAND SWITCH INHIBIT circuit portion
of the preprogrammed band switching network
built-in protection which prevents the system from switching to transmit when a frequency band below
2 MHz is selected or when band switch motor 1A8A4B1 is driving to a new band switch position. As de-
scribed in paragraph 2-78, when transistor 1A6Q10 is biased ON, providing the +19 Vdc to the BAND
MOTOR (+) signal line, the +19 Vdc is also applied to the base of transistor 1A6Q 14, biasing it ON. This
applies a ground through 1A6Q 14 to the BAND SWITCH INHIBIT signal line, which is then applied to
System Control PWB 1A3 as a PA FAULT. Another way of generating a PA FAULT on the BAND
SWITCH INHIBIT signal line occurs when a frequency band below 2 MHz is selected on the receiver-trans-
mitter. When this happens, the six binary coded frequency lines will be coded for one of the two BAND X
frequency ranges as shown in table 2-1. Either one of these input signal combinations produces a logic " 1"
(high) level at the base of transistor 1A6Q 13. This biases 1A6Q13 ON, applying a ground through the
transistor to the BAND SWITCH INHIBIT signal line.
SERVO CONTROLLED ADJUSTMENT OF COIL 1A8A5L1
The servo system consists of the following major elements:
Torque motor 1A8A3B 1 and limit switches 1A8A3S1 and S2 (see figure 3-72).
TORQUE MOTOR 1A8A3B1 AND LIMIT SWITCHES 1A8A3S1 AND 1A8A3S2 (see figure 3-72)
Torque motor 1A8A3B 1 is connected through reduction gears to the shaft of variable series coil
1A8A5L1 and is used to position the rotor, with the attached contact finger, along the length of the coil
winding. As the shaft is rotated, the contact fingers are moved along the flat coil wire, providing an infinitely
fine adjustment of the coil inductance. The wiper contacts short out that portion of the coil winding that
is between the contact point and the output end of the coil (i.e., motor end). The direction and speed of
rotation of the torque motor (and the coil shaft) are controlled by the SERVO IN A (lA14J8, pin 8) and
SERVO IN B (1A14J8, pin 1) signals from Servo Amplifier 1A5 (see paragraphs 2-98 and 2-100). The
direction of rotation, looking from the motor end of the 1A8A3 assembly, is clockwise to decrease the
inductance of coil 1A8A5L1 and counterclockwise to increase the inductance of coil 1A8A5L1. The
1A8A3S1 and S2 limit switches are cam actuated, A gear is connected to the torque motor shaft in such a
way that torque motor 1A8A3B1 is stopped, by opening and then grounding the positive motor line, just
before the wiper contact reaches either end of the coil winding. Limit switch 1A8A3S1 stops the wiper at
the high inductance end of the coil and 1A8A3S2 stops the wiper at the low inductance end of the coil
(near the tubes).