Transmit Operation

TM 11-5820-882-23/TM 06827A-23/2

fication to approximately 1 vrms. The output of the

MHz), it is 12.000 MHz above the rf input frequencies;

driver stage is approximately 100 mw. This stage has a

for the high-band (54 to 80 MHz), it is 12.000 MHz

tuned circuit which tunes the output of the transmiter.

below the rf input frequencies.

Tuning is accomplished by using the built-in tone tuner

b. Filter/I-f Module (1A3). The filter/i-f module

and adjusting C1 on the module. The tone tuner cir-

contains a 12 MHz crystal filter, 12 MHz if amplifier,

cuitry is located in the i-f/a-f module and converts the

18.5 MHz crystal oscillator, and a 6.5 mixer/amplifier

variation in the collector currents of the transmitter

(2nd mixer), The output of the second mixer (6.5 MHz)

stages to a tone frequency when the tone tuner button

is the difference of the 12.0 MHz input and 18.5 MHz

(located on the side of the frame assembly) is depressed.

input from the crystal oscillator.

The final output (approximately 1.5 watts) is routed

c. I-f/A-f Module (1A2). The i-f/a-f module

through one of four band-selected low-pass harmonic

contains a 6.5 MHz i-f amplifier/discriminator, squelch

filters to the antenna coupler (1A5).

circuits, audio amplifier, and a low-pass filter. Other

c.Antenna Coupler Module (1A5). The antenna

functions contained within the module are a tone tuner

circuit and battery saver switch. The input signal to the

coupler module contains the rf transmit/receive diode

if/a-f module is the 6.5 MHz frequency modulated sig-

switching circuits and the antenna matching circuit. Pin

nal from the filter/i-f module. The signal is detected

diodes in the module provide transmit/receive switching

and routed through the low-pass filter to the audio

functions to the antenna matching network. These di-

amplifier. When a handset of other audio accessory is

odes also isolate the transmit/receive circuitry to pre-

connected to the AUDIO connector of the radio set, the

vent the transmitted signal from entering the receiver in-

speaker mute circuit electronically switches off the

put. The antenna matching network provides an imped-

audio signal to the speaker and routes it to the handset.

ance match between the antenna and transmitter circuits

The squelch threshold is adjusted by a potentiometer

(between 50 ohms and 100 ohms). The matching range is

located in the module. The squelch circuit is normally

determined by the position (1 through 4) of the rotary

on when the radio set is turned on. However, squelch

switch located on the module (set the same as the A

can be disabled by turning the function switch to the

switch on the synthesizer). Optimum tuning is ac-

SQUELCH DIS position.

complished by using the field strength meter on the test

set and adjusting L1 on the coupler module (tune for

3-17. Transmit Operation

maximum indication).

The transmitter is packaged in three modules. These

3-8. Frequency Synthesizer (1A7 and

modules are:

a. Modulator/Mixer Module (1A8). The modulator/

1A8)

mixer module contains a speech amplifier and filter, 150

The radio set frequency synthesizer consists of the vco

Hz (squelch tone) buffer, 12 MHz deviation oscillator rf

module (1A7) and the synthesizer module ( 1A9). The

mixer, and two bandswitched, varactor-tuned rf pream-

functon of the frequency synthesizer is to generate the

plifiers. The speech amplifier increases the level of the

required mixer injection frequency and tuning voltage

microphone signal sufficiently for clipping action. The

for the converter and modulator modules when a given

output of the amplifier passes through a low-pass filter

operating frequency is selected. The frequency syn-

before it is superimposed upon a 12 MHz deviation os-

thesizer also determines which band (low or high) is ac-

cillator. The 150 Hz squelch tone from the synthesizer

tive depending upon selection of the operating frequen-

is also routed to the deviation oscillator after passing

cy.

through a buffer and the speech filter network. The fre-

The frequency range of the synthesizer is from

quency modulated output of the oscillator is combined

42.000 MHz to 67.950 MHz which corresponds with a

in a varactor-tuned mixer stage with the frequency syn-

generated tuning voltage range from 2.0 vdc to 11.0 vdc

thesizer output signals to create the desired rf output

respectively. The frequency synthesizer is programmable

frequency. The rf output is amplified by two bandswit-

in 50 kHz steps with the frequency select (A, B. and D)

ched, varactor-tuned rf preamplifiers. For frequencies

switches on the synthesizer module and the CHAN (C)

in the low-band (30 to 54 MHz), the output frequency is

switch on the panel of the radio set.

12.000 MHz below the synthesizer frequency; and for

the high-band (54 to 80 MHz), the output frequency is

b. The frequency range of the synthesizer is

12.000 MHz above the synthesizer frequency.

generated twice to provide low-band radio set operation

from 30,000 MHz to 53.950 MHz (positions 1 and 2 of

b. Transmitter Module (1A4).. The transmitter

the A switch), and high-band radio set operation from

module contains an rf preamplifier, driver, final power

54.000 MHz to 79.950 MHz (positions 3 and 4 of the A

amplifier and low-pass band filters. The output from

the modulator is applied to the preamplifier for ampli-

3-18