KEYER MODULE A9.

TO 31R2-2GRC171-2

TM 11-5820-815-14

NAVELEX 0967-LP-544-5010

temperatures, the negative voltage developed across

A8RT1 and applied to the noninverting input of U7B is

and a transmitter keyer circuit. The squelch operated

more negative than the voltage developed across

relay circuit provides a set of spdt relay contacts at the

resistor R79 and applied to the inverting input of U7B.

receiver-transmitter input/output connector J22 for use

This causes the output of U7B to be negative. As the

external to the AN/GRC-171. The squelch relay is

temperature increases, the resistance of A8RT1

activated whenever the receiver is not muted by squelch

decreases causing the voltage across it to decrease

or when squelch is turned off. Keying the transmitter

also. When the heat-sink temperature at the rf amplifier

inhibits the squelch relay from being activated.

transistors exceeds about 100 degrees Celsius, the

voltage across A8RT1 becomes less negative than the

4-294. The keyer circuit provides interface between the

voltage applied to the inverting input of U7B. This

transmitter key line and external audio loop, current loop,

causes the output of U7B to go positive (approximately

or voltage loop type push-to-talk or keying circuits. For

10 V dc). To prevent the detector from tripping more

audio loop keying, the transmitter can be keyed by a

than once at threshold, resistive divider R75-R76 applies

300- to 3000-Hz tone at a level of -10 to 0 dB mW. An

a positive voltage through resistor R77 to the

optional jumper on keyer module A9 provides for voice

noninverting input of U7B. This provides hysteresis so

operated keying (VOX) through the audio loop. For

that the temperature has to decrease by a certain

current loop keying, the transmitter can be keyed by a

amount before the voltage across A8RT1 becomes more

20- to 60-milliampere dc current loop. For voltage loop

negative than the voltage applied to the inverting input of

keying, the transmitter can be keyed by external push-to-

U7B.

talk or keying circuits that employ 6-, or optional 26-, 28-,

or 100-V dc keying voltages. Strapping options on keyer

4-289. When an antenna vswr fault, or pa/antenna

module A9 allow for selection of one of the voltage

power fault, or a heat-sink temperature of over 100

levels.

degrees Celsius is detected, the voltage at the cathodes

of diodes CR2 and CR3 goes to a positive level. This

4-295. SQUELCH OPERATED RELAY CIRCUIT. Refer

causes the output of the pa power turndown switch, U2A,

to figures 4-7 and FO-32. Squelch comparator A9U1

to be low (ground) to reduce the power output from the rf

compares the voltage applied to the squelch on/ off line

power amplifier module. Otherwise, for no fault, the

to a bias voltage (about -0.26 V dc) developed across

voltage at the cathodes of CR2 and CR3 is about 0 V dc.

resistor A9R2 of voltage divider A9R1-A9R2. The

This causes the output of U2A to be high (open) for

voltage applied to the squelch on/off input is dependent

normal power output.

upon the squelch mode of the receiver which can be one

of the following: squelch off, squelch on and the rf input

4-290. Refer to paragraph 4-272 for a description of the

signal level to the receiver below the squelch threshold,

envelope feedback control switch, U2F-U2D.

or squelch on and the rf input signal above the squelch

threshold. With squelch off (ground applied to the

4-291. The one-shot, U3B, stretches a momentary

squelch on/off input), the bias applied to the inverting

antenna vswr fault or pa/antenna power fault into

input of A9U1 causes the output of A9U1 to be positive

approximately a 300-millisecond pulse.

When a

(about +3.2 V dc). The positive voltage turns squelch

momentary fault is detected, the output of U2A goes to

relay driver transistor A9Q1 on to energize squelch relay

ground. This allows capacitor C5 to discharge to ground

A9K1.

through U2A and develop a negative voltage across

resistor R25. When applied to the inverting input of U3B,

4-296. With the squelch turned on and an rf receive

the negative voltage causes the output of U3B to go high

signal level above the squelch threshold as set by

(about 10 V dc) and develop a positive voltage (about 2.3

squelch potentiometer A10A1R4, the output of squelch

V dc) across resistor R29 of voltage divider R28-R29.

control A4U5B is a positive dc voltage of approximately

Diode CR1 applies the positive voltage to the input of

10 V dc. (Refer to paragraph 4-175 for a discussion of

U2A to hold the output of U2A at ground. At the same

the squelch control circuit.) This positive voltage is

time, capacitor C4 begins to charge toward the voltage

applied through A4R78 and A9R3 to the noninverting

across R29. The positive voltage developed across

input to A9U1 causing the output of A9U1 to be positive

resistor R23 as C4 charges holds the output of U3B high

to energize relay A9K1. Diode A9CR1 limits the positive

as long as the voltage exceeds an approximate +0.54-V

voltage applied to the input of A9U1 to about 0.7 V dc.

dc bias voltage developed across resistor R25 of voltage

divider R26-R25. The RC time constant of C4 and R23

4-297. Under the above conditions with relay A9K1

determines the length of time the output of U3B is held

energized, keying the transmitter applies a ground (key 1

high

input) through diode A9CR4 to the base of A9Q1. The

ground turns A9Q1 off to deenergize A1K1 whenever the

4-292. KEYER MODULE A9.

transmitter is keyed. Diode A9CR5 biases the emitter of

A9Q1 one diode drop above ground to ensure A9Q1 will

4-293. GENERAL. Refer to figure FO-32. The keyer

turn off when a ground is applied to key 1 input.

module is composed of a squelch operated relay circuit

4-50