Table of Contents
Advertisement
2-2 TRANSMITTER CIRCUITS
2-2-1 MICROPHON AMPLIFIER CIRCUIIT
(LOGIC UNIT)
The microphone amplifier circuit (IC16) amplifies the audio
signals from the microphone. The amplified signal is mixed
with the "LI" signal from IC16 (on the LOGIC unit) and
"MOD–MUTE" signal from Q12 and Q13 (on the LOGIC
unit) at the mixer amplifier (IC17). The mixed signal passes
through the high-pass filter (IC18) and low-pass filter (IC18)
via the pre-emphasis circuit (IC17), within +6 dB/octave pre-
emphasis characteristics (300 Hz–3 kHz), to a level needed
for the modulation circuit.
The filtered signal is applied to the mixer amplifier, and is
then mixed with the "DI" signal from IC19. The mixed signal
is applied to the limiter amplifier (TX unit; IC5, pin 3).
2-2-2 MODULATION CIRCUIT (TX UNIT)
The modulation circuit modulates the VCO oscillating signal
(RF signal) using the microphone AF signals.
The "MOD" signal from pin 7, J1 is applied to the limiter
amplifier (IC5, pin 3) via the pin 1, J5. The amplified signal
passes through the modulating controller (Q13) and low-
pass filter (IC5). The filtered signal is adjusted to input level
by the R50, and is then applied to the VCO circuit (D2, D3,
Q2).
2-2-3 YGR-AMPLIFIER CIRCUIT (TX UNIT)
The YGR-amplifier circuit includes the buffer-amplifier (Q4),
pre-driver (Q5) and YGR-amplifier (Q6). The buffer-ampli-
fied signal from the VCO circuit is amplified at the YGR-
amplifier circuit. The YGR-amplified signal is applied to the
power amplifier (PA unit; IC1, pin 1).
The "APCV" signal from the APC control circuit (PA unit) is
applied to the YGR-amplifier (Q6) to stable RF output power.
• MICROPHONE AMPLIFIER CIRCUITS
2
MIC
6
"LI" signal from J9,
pin 33 and J10, pin 2
"DISC" signal from Q13
R65
R71
1
6
MIC
C55 R68
IC16
IC17
7
R70
3
+
2
–
R55
R72
C58
2-2-4 RF POWER AMPLIFIER CIRCUIT (PA UNIT)
IC1 is a power module which provides a stable 45 W of out-
put power.
The amplified signal from the TX unit passes through the
low-pass filter (C16, C17, L6), and is then applied to power
amplifier (IC1). The amplified signal is applied to the RF
detector circuit (D1, D2), and passes through the low-pass
filter (L1–L4, C1, C2, C5, C6, C9, C10). Then, the filtered
signal is applied to the TX antenna connector via the RF
detector circuit (D1 and D2) to control APC circuit.
2-2-5 APC CIRCUIT (PA UNIT)
This circuit controls a current of the power module's first
stage and a current of the driver amplifier to obtain stable RF
output power.
The APC mismatch detector circuit consists of C3, C7, D1,
D2, L3. When the antenna impedance is matched at 50 Ω,
the detected voltage by D1 and D2 is at its minimum. The
detected voltage is applied to a differential amplifier (IC3, pin
3). The APC reference voltage is applied to pin 1,of IC3.
When the antenna impedanceis mismatched, the voltage of
IC3 (pin 3) exceeds the reference voltage of IC3 (pin 1). The
output level from IC3 (pin 4) decreases. Q1 amplifies the
current from the differential amplifier (IC3) which controls
Q2. Q2 changes the supply voltage to IC1.
This decreases the output power from the power amplifier
(IC1) until the input voltage of IC3 (pin 6) reaches the same
level as pin 5 of IC2.
–
7
+
IC18
HPF
1
"DI" signal from J9, pin 6
and J10, pin 7
R73
2 - 2
6
7
LPF
IC19
To IC5,
pin 3 (TX unit)
2
1
Advertisement
Table of Contents
