Section IV. NONCONVENTIONAL CIRCUITS

TM 11-5820-873-34

A drive signal is received at either 2XA6-4 or 2XA6-5 for

phase correction. The drive signal is a ground supplied

CAUTION

by Control Logic Board 2A1. When no ground is present

If a drive signal (ground) is placed on

at either 2XA6-4 or 2XA6-5, both are at + 28 VDC. Thus

2XA6-4 and 2XA6-5 simultaneously,

the servo amp is cutoff from driving in either direction.

the transistors will be destroyed A

A drive signal (ground) at 2XA6-4 causes 2A6Q1 to

positive brake signal at 2XA6-12

conduct. Transistor 2A6Q1 then triggers 2A6Q2 and

anytime the motor is being driven

2A6Q4 on. When 2A6Q2 conducts, +28 VDC is applied

will also destroy transistors.

to 2M1-1. When 2A6Q4 conducts, a ground is provided

to 2M1-2. This causes 2M1 to rotate in one direction.

2-21. 3 dB Attenuator Detailed Functional Operation

Removing the ground level drive signal from 2XA6-4

(Fig FO-32)

cuts off 2A6Q1. The DC excitation to 2M1 is removed

The 3 dB Attenuator consists of 2K4, 2CR1, and a 3 dB

and rotation stops. A drive signal (ground) at 2XA6-5

pad containing 2C4, 2R3, 2R4, 2R5, 2R6, 2R7 and 2R8

causes 2A6Q6 to conduct. Transistor 2A6Q6 then

The 3 dB circuitry is used to prevent transmitting into a

triggers 2A6Q5 and 2A6Q3 on. When 2A6Q5 conducts,

possible open or short circuit. The accomplish this, a 3

+ 28 VDC is supplied to 2M1-2 When 2A6Q3 is

dB pad is switched in series with the transmission line.

conducting, ground is present at 2M1-1 The motor then

Switching is accomplished thru 2K4 Control Logic Board

rotates In the opposite direction Again, removing the

2A1 operates 2K4. The pad is switched in when coupler

ground level drive signal at 2XA6-5 this time, cuts off

tuning is initiated. When reflected power drops below

2A6Q6 Motor 2M1 stops rotating. A positive braking

threshold, the 3 dB pad is taken out of the RF path If

signal is applied at 2XA6-12 to prevent overshoot and

reflected power goes above threshold the pad will be

oscillation of 2M1. The positive brake signal causes

switched in series in the RF path again.

both 2A6Q3 and 2A6Q4 to conduct and place a ground

at 2M1-1 and 2M1-2.

Section IV. NONCONVENTIONAL CIRCUITS

2-22. Key Line

(Fig. FO-8)

amplifier bias circuit. Also, low voltage transmit (+ 12T)

Keying the radio set to transmit mode is accomplished

is switched in, low voltage receive (+ 12R) is grounded

by grounding the key line. For normal operation a

through 1A5R9 and the front panel meter is switched to

ground from the mic key, the cw key, or AUDIO

output monitor If the band channeling motor 1A5Bl is

connector 1A8J2-G will establish transmit mode. During

running, 1A5K1 is energized opening contacts 12 and 4

tuning, the Antenna Coupler Unit grounds the key line at

to prevent transmit operation.

1A8J4-P to switch the radio set to transmit mode for

tuning purposes.

b. CW Keying. For CW transmission the key line is

NOTE

ground in the following manner The mode switch must

The Antenna Coupler Unit must be

be set to CW When the CW key is depressed a ground

connected

ACCESSORY

is applied to the base of 1A3A3Q12 thru 1A1S13B

connector 1A8J4 or 1A8J4-p and

contacts 2 and 6. Transistor 1A3A3Q12 is turned on

1A8J4-n jumpered for keying to

and applies ground to terminal 1A3E26 through

occur.

1A3A3Q14. The key line then functions as described in

a. LSB, USB and AM Keying. In these modes the

paragraph 41a. above.

key line is grounded when the handset press to talk

switch is depressed. This ground is applied to terminal

c. Tuning Cycle Keying. When the mode switch is

1A3E26 on the key line. From there the key line routing

set to CPLR TUNE KW, a ground is to the key line

is to the Antenna Coupler Unit and through relay 2K1

through 1A1S13A-8 and 10. But in this case 2K1 is

closed contacts 11 and 3. Diode 1A8CR6 prevents the

energized by the ground and 2K1-11 and 3 open The

grounded key line from energizing 2K1 at this time. The

key line ground is then controlled by the Control Logic

key line then returns to the transceiver and goes through

Board (2A1) output on pin 7. From this point on, key

closed contacts 12 and 4 of lA5Kl to energize 1A5K2.

line operation is as described in paragraph 2-22a.

Energizing 1A5K2 also energizes 1A8K1 through 1A5K2

above Refer to Chapter III Section III for Control Logic

now closed contacts 1 and 5. With 1A5K2 and 1A8K1

Board 2A1 operation.

energized, all switching is complete for LSB, USB and

AM transmit. The RF power amplifier is switched to the

low pass filter and + 28 VDC is applied to the power

2-22