Figure 3-7. Power Amplifier Block Diagram

TM 11-5820-919-12

from

the second converter With USB selected, the upper if

circurits via trhe age autonatic again control signal.

product is passed [80 MHz 5 MHz Xmt Audio] the first

converter then mixed the bandpass filter if. with a

3-35 POWER AMPLIFIER (Figure 3-7)

The power

specific frequency between 77 and 105 MHz (75 MHz +

amplifier boosts the

0.30-watt output from the

Xmt RF frequency) The specific mixing frequency is

modulator/demodulator to provide 20-watt (normal) rf

determined At the control panel, made in the synthesizer

power at the antenna. The Xmt RF is preamplified to 2

and precalculated to produce the desired Xmt RF. For

watts in t he output stage. It is then a amplified to about

example, with 5 MHz and US B selected at the control

27 watts in t he output stage. (About 7 watts is lost in the

panel, the LO is 80 MHz and the Xmt RF is {80 MHz

filter and antenna tuner. ) The DC-DC converter

70MHz Xmt Audio ] or 5 MHz + Xmt Audio.

provides the +30.5v Regulated voltage for the output

stage. The tuner dc source generates +16v Regulated

for use by the antenna tuner during impedance matching

3-34. In receive operation, the flow direction is reverse.

. This is triggered by the Tune In Progress signal from t

The same circuits are used. Except t hat certain

he antenna tuner. The tuner dc source compensates for

amplifiers are switched into and out of the system. The

changes in battery v outage and temperature. The power

Rev RF mixes with three 77 105 MHz LO in the first

monitor circuits use the vswr signal from the harmonic

converter to create upper and lower if products...The

filer to protect the power amplifier. If the antenna is

upper if product is filtered out at filter FL1. The l owe

badly matched to the radio set power reflects back at the

product (75 MHz if) is passed to the second converter

power reflects back at the power amplifier. This could

where it mixes with either 70 (USB) or 80 MHz (LSB.

cause damage. When a poor match occurs, the power

The 5 MHz if, product is passed through filter FL2 while

monitor disables the driver tuning (Tune Check Enable)

the upper if. Product is filtered out. The 5-MHz if, is

and sends ALC Feedback signal

to the

mixed with 5 MHz in the third converter to create the

modulator/demodulator. The ALC controls the rf power

Rev Audio. The level of the receive signal is c controlled

output level of the receiver/exciter in transmit operation.

at the second and third converters bay the hybrid audio

Figure 3-7. Power Amplifier Block Diagram

3-10