4 - 2
4-1-5 AF AMPLIFIER CIRCUIT
The AF amplifier circuit amplifies the detected signals to
drive a speaker. The AF circuit includes an AF mute circuit
for the squelch.
AF signals from IC1 (pin 9) are passed through the analog
switch (IC12, pins 10, 11), and are applied to the de-empha-
sis circuit (R118, C182). The de-emphasis circuit is an inte-
grated circuit with frequency characteristic of –6 dB/octave.
The integrated signals are applied to the active filters (Q24,
Q25). Q24 functions as a high-pass filter to suppress
unwanted lower noise signals and Q25 functions as a low-
pass filter to suppress higher noise signals.
The filtered signals are passed through the [VOLUME] con-
trol, and are then applied to the AF power amplifier (IC14,
pin 1). The output signal from IC14 (pin 4) drives the inter-
nal (external) speaker.
4-1-6 SQUELCH CIRCUIT
A squelch circuit cuts out AF signals when no RF signals are
received. By detecting noise components in the AF signals,
the squelch circuit switches the AF mute switch.
A portion of the AF signals from the FM IF IC (IC1, pin 9)
pass through the squelch adjustment pot (R33), and are
then applied to the active filter section (IC1, pin 8). The
active filter section amplifies and filters noise components.
The filtered signals are applied to the noise detector section
and output from pin 14 as the “SQLI” signal. The “SQLI” sig-
nal is amplified at the DC amplifier (IC20) and applied to the
CPU (IC16, pin 39) as the “SQL” signal. The CPU analyzes
the noise condition and outputs the “RMUTM”, “RMUTS”
signals to toggle the AF mute switches (Q26, Q27).
4-2 TRANSMITTER CIRCUITS
4-2-1 MICROPHONE AMPLIFIER CIRCUIT
The microphone amplifier circuit amplifies audio signals with
+6 dB/octave pre-emphasis from the microphone to a level
needed at the modulation circuit.
The AF signals from the microphone are amplified at the
microphone amplifier (IC11a) via the analog switch (IC10,
pins 11, 10). A capacitor (C214) and resistor (R147) are con-
nected to the amplifier to obtain the pre-emphasis charac-
teristics.
The amplified signals are applied to the IDC amplifier
(IC13a, pin 2) via the analog switch (IC12, pins 9, 8 and pins
4, 3) and are passed through the splatter filter (IC13b) to
suppress unwanted 3 kHz or higher signals. The filtered sig-
nals are then applied to the modulation circuit.
4-2-2 MODULATION CIRCUIT
The modulation circuit modulates the VCO oscillating signal
(RF signal) using the microphone audio signals.
Audio signals from the splatter filter (IC13b) pass through
the frequency deviation adjustment pot (R172) and are then
applied to the modulation circuit (D8) to change the reac-
tance of D8, and modulate the oscillated signal at the TX-
VCO (Q7).
4-2-3 DRIVE AMPLIFIER CIRCUIT
The drive amplifier circuit amplifies the VCO oscillating sig-
nal to a level needed at the power amplifier.
The VCO output is buffer-amplified by Q9 and Q10, and is
then applied to the Tx/Rx switch (D12). The transmit signal
from the Tx/Rx switch is amplified to the pre-drive (Q11) and
drive (Q12) amplifiers to obtain an approximate 200 mW sig-
nal level. The amplified signal is then applied to the RF
power amplifier (IC3).
4-2-4 POWER AMPLIFIER CIRCUIT
The power amplifier circuit amplifies the driver signal to an
output power level.
IC3 is a power module which has amplification output capa-
bilities of about 35 W with 300 mW input. The output from
IC3 (pin 4) is passed through the antenna switching circuit
(D16) and is then applied to the antenna connector via the
low-pass filter.
4-2-5 APC CIRCUIT
The APC circuit stabilizes transmit output power.
The RF output signal from the power amplifier (IC3) is
detected at the power detector circuit (D14, D15, L21) and
is then applied to one of the differential amplifier inputs
(Q16, pin 5) via the High/Low control circuit (R84, Q17). The
applied voltage controls the differential amplifier output
(Q16, pin 2) and the bias voltage control (Q14). Thus the
APC circuit maintains a constant output power.
• APC circuit
T8
D14
D15
L21
/TMUT
VCC
HI/LO
"TXDET" signal
to the CPU
Q14
Q16
Q15
Q17
R84
Q12
Drive
amp.
RF signal
from PLL
to antenna
RF detector
circuit
APC control circuit
Power module
IC3
Q18
