Kenwood TK-3202 User Manual download pdf (Page 10)

TK-3202/3206

CIRCUIT DESCRIPTION

Fig. 6 Microphone amplifier

Fig. 7 Drive and final amplifier and APC circuit

4. Transmitter System

1) Microphone Amplifier

The signal from the microphone passes through IC301.

When encoding DTMF, it is turned OFF for muting the

microphone input signal by IC301.

The signal passes through the Audio processor (IC301) for

the maximum deviation adjustment, and goes to the VCO

modulation input.

2) Drive and Final Amplifier

The signal from the T/R switch (D101 is on) is amplified by

the pre-drive (Q101) and drive amplifier (Q102) to 50mW.

The output of the drive amplifier is amplified by the RF power

amplifier (Q103) to 4.0W (1W when the power is low). The

RF power amplifier consists of two MOS FET stages. The

output of the RF power amplifier is then passed through

the harmonic filter (LPF) and antenna switch (D103 and

D122) and applied to the antenna terminal.

From

T/R SW

(D101)

DRIVE

AMP

POWER AMP

LPF

ANT

D103

D122

VGVGVD

Q102 Q103

Pre-DRIVE

AMP

Q101

VDD

AMP

Q100

R127

R128

R129

IC101

(1/2)

IC101

(2/2)

PCTV

(IC405)

IC301

IC405

LPF

DTMF

QTTCXO

QTVCO

CPU

AGC

VCO

MIC

TCXO

LPF

AQUA

3) APC Circuit

The APC circuit always monitors the current flowing through

the RF power amplifier (Q103) and keeps a constant current.

The voltage drop at R127, R128 and R129 is caused by the

current flowing through the RF power amplifier and this

voltage is applied to the differential amplifier IC101(1/2).

IC101(2/2) compares the output voltage of IC101(1/2) with

the reference voltage from IC405. The output of IC101(2/2)

controls the VG of the RF power amplifier, Drive amplifier

and Pre-Drive amplifier to make both voltages the same.

The change of power high/low is carried out by the change

of the reference voltage.

4) Encode Signalling

(1) QT/DQT

QT,DQT data of the QTTCXO Line is output from pin 28 of

the CPU. The signal passes through a low-pass CR filter

and goes to the TCXO(X1).

The QT,DQT data of the QTVCO Line is output from pin 24

of the CPU. The signal passes through a low pass CR filter,

mixes with the audio signal, and goes to the VCO modulation

input. TX deviation is adjusted by the CPU.

(2) DTMF

High-speed data is output from pin 2 of the CPU. The signal

passes through a low-pass CR filter, and provides a TX and

SP out tone, and is then applied to the audio processor

(IC301). The signal is mixed with the audio signal and goes

to the VCO.

TX deviation is adjusted by the CPU.

(3) MSK (Fleet Sync)

Fleet Sync utilizes 1200bps and 2400bps MSK signal is

output from pin 6 of IC301. And is routed to the VCO.

When encoding MSK, the microphone input signal is muted.

5. Power Supply

There are four 5V power supplies for the microprocessor:

5M,5C,5R, and 5T. 5M for microprocessor is always output

while the power is on. 5M is always output, but turns off when

the power is turned off to prevent malfunction of the

microprocessor.

5C is a common 5V and is output when SAVE is not set to

OFF.

5R is 5V for reception and output during reception.

5T is 5V for transmission and output during transmission.

6. Control Circuit

The control circuit consists of a microprocessor (IC405) and

its peripheral circuits. It controls the TX-RX unit. IC405 mainly

performs the following:

(1) Switching between transmission and reception by the

PTT signal input.

(2) Reading system, group, frequency, and program data

from the memory circuit.

(3) Sending frequency program data to the PLL.

(4) Controlling squelch on/off by the DC voltage from the

squelch circuit.

(5) Controlling the audio mute circuit by the decode data

input.

(6) Transmitting tone and encode data.

1) Frequency Shift Circuit

The microprocessor (IC405) operates at a clock of

7.3728MHz. This oscillator has a circuit that shifts the

frequency by BEAT SHIFT SW (Q407, Q408).

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Kenwood TK-3202 User Manual Page 10

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