4-1-4 S-METER CIRCUIT (PLL UNIT)
Aportion of signals passed from FI202 is amplified at S-
meter amplifier Q205 and Q206, and is detected at
voltage doubler rectifiers D201 and D202. These
signals are then applied to meter comparator IC105A
on the MAIN UNIT.
4-1-5 AF CIRCUIT (MAIN UNIT)
AF signals output from pin 9on IC201 are applied to the
MAIN UNIT, and pass through ade-emphasis circuit
consisting of R127 and Cl 17. These signals are then
amplified at AF controller Q105. This de-emphasis cir-
cuit is an integrator circuit with frequency
characteristics of 6dB/oct.
The AF amplifier circuit consists of Q1 16~Q122. The
input section (Q1 16and Q1 17) functions as adifferen-
tial amplifier to ensure stable operations and asuitable
frequency response by the negative feedback network
of R152 and R149. The AF power amplifier circuit is a
complementary SEPP circuit with aDarlington connec-
tion of Q1 19~Q1 22. This circuit drives the speaker.
When the power source voltage is more than 10V,
D106 and voltage regulator Q106 limit output voltage
and output power, stabilizing the bias.
Astandby current suppressor (Q1 32) is installed to sup-
press the current and residual noise while the squelch is
closed.
4-1-6 SQUELCH CIRCUIT (MAIN UNIT)
Noise components from pin 9of IC201 are fed to active
filter IC101B through SQUELCH CONTROL R126.
This active filter is ahigh-pass filter, and amplifies ap-
proximately 20kHz noise components. The noise com-
ponents are then rectified by D103 and converted to
DC voltage at R1 19, R1 20, Cl 11,and Cl 12. The DC
voltage passes through inverters IC103B and IC103A
to obtain aTTL level from alinear level.
AF controller 0105 is turned OFF by the "HIGH"
voltage level from pin 2of IC103A. Output signals from
pin 2of IC103A are also fed to MPU IC401 in the
LOGIC UNIT through D104 as asquelch signal.
When no RF signal is received, noise rectified output
voltages from D103 are "HIGH". Pin 2of IC103A thus
becomes "HIGH" and 0105 turns OFF. AF output is
then cut OFF.
In transmit mode, T-l- 5signals are applied to pin 9of
IC103B via D105 to turn 0105 OFF.
4-1-7 1St LO CIRCUIT (VCO AND PLL UNITS)
450MHz band LO signals from the VCO UNIT are buffer
amplified at 0208 and fed to transmit/receive swit-
ching circuit D208 in the PLL UNIT. The signals are then
applied to the base of 1st mixer Q203 as 1st LO signals.
4-2 TRANSMITTER CIRCUITS
4-2-1 MICROPHONE AMPLIFIER CIRCUIT
(MAIN UNIT)
AF signals from the INTERNAL MICROPHONE or from
EXTERNAL MIC JACK J202 are amplified at alimiter
amplifier consisting of Q101~Q104.
This limiter amplifier is formed by anegative feedback
circuit with frequency characteristics set at 6dB/oct.
from 300Hz to 3kHz. This causes the limiter amplifier
to function as apre-emphasis circuit. Output from the
limiter amplifier is similar to arectangular waveform
and includes harmonic components.
Harmonic components higher than 3kHz are attenuated
by splatter filter IC101A.
AF signals from IC101A pass through modulation ad-
justing trimmer pot R226 in the PLL UNIT and are then
applied to the anode of D703 in the VCO UNIT for per-
forming frequency modulation.
4-2-2 BUFFER AMPLIFIER CIRCUIT (PLL UNIT)
430 or 440MHz band signals output from the VCO
UNIT are buffer amplified by 0208 and pass through
transmit/receive switching circuit D209. They are then
amplified at predriver 021 1,and driver 021 2, thus ob-
taining awideband of 150mW.
4-2
