Transmitter Circuit; Microphone And Modultion Level Adjustment Circuit; Drive And Final Power Amplifier And Automatic Power Control Circuit - Kenwood TK-8180 Service Manual

2-5. Squelch Circuit
The output signal from IC172 enters FM IC again, then
passed through a band-pass filter.
The noise component output from IC172 is amplified by
Q175 and rectified by D173 to produce a DC Voltage corre-
sponding to the noise level. The DC voltage is sent to the
analog port of the CPU (IC404).
IC172 outputs a DC voltage (RSSI) corresponding to the
input of the IF amplifier.

3. Transmitter Circuit

The transmitter circuit consists of the following circuits : 3-
1 microphone circuit, 3-2 modulation level adjustment circuit,
3-3 driver and final power amplifier circuit, and 3-4 automatic
power control circuit.
3-1. Microphone Circuit
The audio signal from the microphone goes into TX-RX
unit (X57-699) from the display unit (X54-348) and passes
through the mute switch (Q416). The audio signal is ampli-
fied by the microphone amplifier (IC414) and is input into the
TXIN terminal of the audio processor (IC415) after passing
through the multiplexer (IC413).
The input audio signal is output from the MOD terminal of
the audio processor (IC415) and is amplified by the audio fre-
quency amplifier (IC412) after passing through the electric
volume (IC410).
DISPLAY UNIT
(X54-348) TX-RX UNIT (X57-699)
MIC
J901
Mojular
jack
Q307
MOD TX VCO
VCXO
MB
16.8MHz
X301
Fig. 3

Drive and Final power amplifier and automatic power control circuit

CIRCUIT DESCRIPTION
Q416 IC414 IC413
Multi-
SW AMP
plexer
SW Q417
D-SUB
MI2
Fig. 2

Microphone and modultion level adjustment circuit

Q311 Q313 Q1
Buff Drive Drive
AMP AMP AMP
PC
MP
3-2. Modulation Level Adjustment Circuit
The audio signal amplified by the audio frequency ampli-
fier (IC412) is added to the low speed data LSD passed
through the low pass filter (IC409). The combined signals is
supplied to the VCO (voltage controlled oscillator) and the
VCXO (voltage controlled crystal oscillator) X301, respec-
tively.
3-3. Driver and Final Power Amplifier Circuit
The transmit signal obtained from the TX VCO buffer am-
plifier Q311, is amplified to approximately +17dBm by the
driver amplifiers Q313, Q1 and Q2. This amplified signal is
passed to the power amplifier module (power module) IC1,
which consists of a MOS-FET amplifier and is capable of
transmission output power.
3-4. Automatic Power Control Circuit
The automatic transmission power control (APC) circuit
stabilizes the transmitter output power at a predetermined
level by detecting the power module output with a diodes
D6, D7 and D8. Diodes D6, D7 and D8 apply a voltage to DC
amplifier IC72 (A/2). IC72 (B/2) compares the APC control
voltage (PC) generated by microprocessor IC404 and DC am-
plifier IC71 (A/2, B/2) with the detection output voltage
from IC72 (A/2) to control the Vgg pin of IC1, and stabilizes
transmission output.
The APC circuit is configured to protect over-current of the
power module due to fluctuations of the load at the antenna
end and to stabilize transmission output at voltage and tem-
perature variations.
IC415
AQUA-L
TXIN MOD
D-SUB
DI
IC409
LPF
LSDO
Q2 IC1
Drive Final D2,D3,
AMP AMP D11
SW
Gate
D6
bias
DET
DC DC
AMP AMP
IC71 IC72
TK-8180
IC410 IC412
MOD
AMP
(for VCO)
DAC IC408
DC
MB
AMP
(for VCXO)
ANT
D7 D8
DET DET
17