Phase Preamp

TM 11-5820-873-34

interval when C1 mm pulse exists. If this action were

a Phase Preamp. The Phase Preamp consists of

not taken, and phase were positive when 2C1 reached

differential amplifier 2A2U1, 2A2CR1, 2A2CR2 and

minimum, C1 Home FF would be set and 2A2Q6 and

related components. A + 10 VDC reference is applied

2A2Q7 would be turned on at the same time Diode

to 2A2U1-4.

The 2A2U1-5 input is a DC level

2A2CRll is connected to the 50 (-) line and removes the

proportionate to phase angle. The 2A2U1-10 output is

drive from 2A2Q7 when the reflected power falls below

referenced at a + 10 VDC level which is the null output

the threshold If the unit is homing and the 50 ohm

level. When phase angle goes negative, 2A2U1-10

threshold point occurs before a positive phase angle

generates a corresponding output level below +10 VDC.

occurs, the home drive will be terminated by 2A2CR11.

If phase angle is positive, 2A2U1-10 is at a

Variable capacitor 2C1 will overshoot and the resultant

corresponding level above +10 VDC Operational levels

positive phase angle will reset the C1 Home FF.

of 2A2U1-10 are between ground and +28 VDC.

However, the driven elements have come to rest and

b. Phase Level Changer. Components of this

slight servo action will correct the phase error to zero

function are 2A2Q1, 2A2Q2, 2A2Q3 and associated

e. C1 Drive Inhibit.

Gate 2A2U2C, 2A2Q5,

circuitry. An input, to the Phase Level Changer, above

2A2CR8 and associated resistors make up the C1 Drive

+10 VDC controls 2A2Q1 conduction Transistor 2A2Q1

Inhibit. The C1 home signal and a C1 Home FF reset,

output, in turn, controls 2A2Q3 which establishes a drive

logic 0, causes a logic 1 at 2A2U2C-8. The logic 1

signal to the Phase Servo Preamp positive drive. Also

triggers 2A2Q5 to short out the drive signal from the

2A2Q3 provides an output to the Phase Positive Logic

Phase Level Changer during the home cycle. This

Generator. If the Phase Level Changer input is below +

action is necessary to prevent driving 2A2Q6 while

10 VDC, 2A2Q2 conducts to provide a drive signal to

2A2Q7 is driving during the home cycle. Transistor

the Phase Servo Preamp negative drive.

2A2Q5 is also utilized to remove the drive from the

c Phase Positive Logic Generator. Transistor

phase servo during intervals when reflected power is

2A2Q4 functions as a logic level generator. When

below threshold. This is accomplished by the 50 (+)

triggered by the Phase Level Changer, it establishes a

signal triggers 2A2Q5 through 2A2CR8 and 2A2R21.

logic level 0. This logic 0 indicates a positive phase

f. Phase Servo Preamp.

The Phase Servo

angle to board 2A2 flip-flop functions.

Preamp contains 2A2CR6, 2A2CR9, 2A2CR10,

d. C1 Home Flip-Flop. The C1 Home flip-flop is

2A2CR11, 2A2Q6, 2A2Q7 and required resistors. A

comprised of 2A2U2A-B-C, 2A2Q5, 2A2CR3, 2A2CR4,

positive phase signal triggers 2A2Q6 to supply a drive

2A2CR5 and associated components When power is

signal at 2XA2-4 A negative phase signal triggers

first applied, this FF resets and 2A2U2A-3 is at logic 0.

2A2Q7 to provide a drive signal at 2XA2-5 Transistor

A C1 home signal, logic 0 at 2XA2-6, to 2A2U2A-2 sets

2A2Q6 is cutoff, when reflected power is below

the FF. The logic 1 at 2A2U2A-3 then triggers Phase

threshold, through 2A2CR9. Similarly, 2A2Q7 is cutoff

Servo Preamp 2A2Q7 to provide a drive signal at 2XA2-

through 2A2CR10 Cutoff 2A2Q7 is also accomplished

5. The same logic 1 is used by the C1 Drive Inhibit

through 2A2CR6 at C max or through 2A2CR11 by a 50

function. The C1 Home FF is reset (home cycle

(-) signal at 2XA210

terminated) by logic 0 on the collector of 2A2Q4 or logic

g. Amplitude Preamp. The Amplitude Preamp is

0 on the C min line. In other words, the capacitor will be

comprised of 2A2U3, 2A2CR20, 2A2CR21 and

driven toward maximum until a positive phase angle is

associated components A + 10 VDC reference is applied

detected or until the capacitor reaches maximum

to 2A2U3-4.

The 2A2U3-5 input is a DC level

capacity A positive phase angle resets the C1 Home FF

proportionate to impedance magnitude. The 2A2U3-10

by a logic 0 at 2A2U2B-5 C max resets the FF by

output is referenced at a + 10 VDC level which is the

applying a logic 0 to 2A2U2A3 thru 2A2CR7. The C

null output level. When impedance is above 50 ohms, a

max line also shorts out the output to 2A2Q7 through

negative voltage is applied to 2A2U3-5 Conversely,

2A2CR6. This action is required because the phase

impedance below 50 ohms means a positive input to

may still be negative when 2C1 reaches maximum

2A2U3-5. With a positive at 2A2U3-5, the output of

capacitance and, although the C1 home function is

2A2U3-10 goes to a corresponding level above + 10

terminated the negative phase would try to drive the

VDC. With a negative input to 2A2U3-5, 2A2U3-10

capacitor beyond the end stop. Diode 2A2CR3 shorts

provides a corresponding output below + 10 VDC.

out the positive phase drive to 2A2Q6 during the interval

Operational levels of 2A2U3-10 are between +28 VDC

of the C1 home signal. This prevents the initial turn on

and ground.

of the transmitter from generating a positive phase

angle and causing 2A2Q7 and 2A2Q6 to be turned on

h. Amplitude Level Changer. The Amplitude Level

simultaneously. Diode 2A2CR4 resets the C1 Home FF

Changer includes 2A2Q10, 2A2Q11, 2A2Q12 and

when the capacitor reaches minimum capacitance and

forces the capacitor toward maximum. Diode 2A2CR5

shorts out the positive phase drive during the time

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