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Transmitter circuit, Tk-8180, Circuit description – Kenwood TK-8180 User Manual

Page 17

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TK-8180

17

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).

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.

AMP

SW

SW

IC414

Q416

Q417

AMP

DC

AMP

IC408

LPF

IC409

IC410

IC412

IC415

D-SUB

MI2

AQUA-L

MOD

D-SUB

DI

DAC

MB
(for VCXO)

MOD
(for VCO)

MIC

J901
Mojular
jack

DISPLAY UNIT
(X54-348)

TX-RX UNIT (X57-699)

IC413

Multi-

plexer

TXIN

LSDO

TX VCO

VCXO

16.8MHz

Q307

Q313
Drive

AMP

Q311

Buff

AMP

Q1

Drive

AMP

Q2

Drive

AMP

IC1

Final
AMP

X301

MOD

MB

DC

AMP

DC

AMP

PC

MP

SW

D2,D3,

D11

DET

DET

D6

D7

DET

D8

ANT

Gate

bias

IC71

IC72

CIRCUIT DESCRIPTION

Fig. 2

Microphone and modultion level adjustment circuit

Fig. 3

Drive and Final power amplifier and automatic power control circuit