Power Probe A1A6 - TM-11-5825-271-340014

TM 11-5825-271-34

(e.g, voice modulation), does not produce the dc voltage.

2-19. Power Probe A1A6

Therefore, synchronous detector Q4/Q5 prevents the

(fig. FO-9)

external voice input from interfering with the modulation

a. Transformer T1 (winding B) and T2 form the

monitoring circuits.

voltage and current arms of a forward/reflected power

(2) Comparator U1-A compares the dc voltage

bridge from which dc voltages are obtained. The

from synchronous detector Q4/Q5 with a reference

voltages (proportional to forward power, reflected power,

voltage established by the ratio of R11 and R12. When

rf voltage, and rf current) are used for metering,

the input at pin 5 of U1-A is more positive than the

shutdown control and current limiting A dc voltage

reference voltage at pin 4 of U1-A, the output from U1-A

developed at the collector of Q1 is used to compensate

at pin 2 is high. Conversely, when pin 5 of U1-A is less

for the pedestal of the detector diodes (CR1 through

positive than the voltage at pin 4 of U1-A, the output from

CR4) and improves the measurement accuracy at low-

U1-A (pin 2) Is low. The reference voltage at pin 4 of

power levels.

U1-A is chosen such that during keying the output from

b. Diode CR1 detects the rf carrier level. Filter

U1-A makes a low-to-high transition each time keying is

L1/C2 transforms the detected signal to an audio signal

gated on. The output from the modulation detector and

superimposed upon a dc voltage proportional to the rf

threshold comparator circuit is applied to the normal and

carrier level The voltage at P1-12 is used by the monitor

special shutdown circuits.

assembly A1A7 to control the shutdown function

b. Carrier Threshold Comparator. The signal from

c. Secondary winding A of transformer T1 subtracts

the wiper of the CARR THRESHOLD potentiometer R3

the voltage components from the signals at the junction

is filtered by R39 and C13 to remove the audio

of R3 and CR4 to produce, at the cathode of CR2, a dc

component. The resulting dc level, proportional to the

voltage proportional to the rf current The current limit

carrier level, is compared with a reference voltage

signal, at P1-2, is applied to the mark/space modulator in

determined by the ratio of R36 and R37. During normal

the exciter assembly A1A2 The dc outputs at P1-6 and

operation, the dc voltage at pin 9 of U1-C is more

P1-4, derived through CR4 and CR3, are indicative of the

positive than the reference voltage at pin 8 of U1-C

forward and reflected power respectively

Therefore, the output from U1-C (pin 14) remains high as

long as the carrier level is greater than the threshold

2-20. Monitor Assembly A1A7

setting of R3. If a malfunction or some abnormal

(fig. FO-10)

operating condition causes the carrier level to drop by 3

a. Modulation Detector and Threshold Comparator.

dB or more, the output from comparator U1-C changes

The input signal from the power probe A1A6 is received

state, i e, pin 14 of U1-C goes low from its normally high

at P1-12 through potentiometer R2 The input signal is a

state. The output from U1-C (pin 14) is fed to the normal

dc voltage proportional to the carrier level and contains

shutdown circuit

an ac component indicative of the modulation level. The

c. Normal Shutdown Control.

The normal

signal from the wiper of R2 is buffered by emitter-follower

shutdown control circuit is controlled by both the carrier

Q1 and applied to two transistors, Q2 and Q3 Transistor

and modulation threshold comparators. Associated with

Q3 and capacitor C4 couple the ac component (audio) to

the circuit are a NORM/BYP (operate/test) switch S1 and

the AUDIO MON jack J2 on the control panel through

a NORM (within limits) indicator DS1.

P1-15, while transistor Q2 couples it to a synchronous

(1) When the modulation is within limits and

detector formed by Q4 and Q5 When the modulation

keying is present, the output from U1-A is high during

threshold level is correctly set at - 3 dB by R2 and the

keying (mark) and low during a space. Provided the

modulation depth is at its normal level, the amplitude of

output from U1-C is high (carrier level within limits), the

the signal at the collector of Q2 is approximately 2V p-p.

positive-going transitions from U1-A cause Q6 to

(1) The 1020 Hz tone input at P1-9 causes Q5

momentarily switch on. If a keying failure occurs, or if

to switch on and off at a 1020 Hz rage Transistor Q4,

the modulation level falls below the preset level, the

which also switches on and off at 1020 Hz, acts as a

transitions at the base of Q6 are no longer present,

gated dc restorer to the signal from C3. When the

causing it to remain switched off. Similarly, if the carrier

detected modulation signal is at the same frequency and

level falls below the present threshold, the output from

in phase with the 1020 Hz tone input, a positive dc

U1-C goes low and Q6 remains switched off,

voltage is obtained at the junction of C3/R9. Any

disregarding the positive-going transitions from U1-A.

component of the modulation signal that is not the same

(2) Whenever Q6 is switched on, capacitor C9

frequency, or out of phase with the 1020 Hz,

is discharged. When Q6 is off, C9 is constantly charged

through R17. The voltage across C9 is compared with

2-9