Kenwood TH-K2AT, K2E, K2ET ■Microphone Amplifier Circuit, Fig. 5 Microphone amplifier circuit, ■Modulation Circuit, ■Drive and Final Circuit, ■Transmission/Reception Switching Circuit

TH-K2AT/K2E/K2ET

CIRCUIT DESCRIPTION

Transmitter System

■Microphone Amplifier Circuit

The audio signal from the microphone passes through a high-pass filter (IC5) and enters a microphone amplifier (IC16).

The signal passes through a pre-emphasis circuit, limiter amplifier and splatter filter inside the microphone amplifier. The splatter filter will remove distortion outside the audio band.

IC16

MIC AMP

MIC	IC5				Limiter
	HPF	6						1	VCO
				Pre-		Splatter
			emphasis				filter

Fig. 5 Microphone amplifier circuit

■Modulation Circuit

The audio signal amplified by the microphone amplifier (IC16) passes through a semi-fixed volume (VR5) for modulation adjustment, and goes to the VCO modulation varicap (D6) for variable reactance phase modulation.

■Drive and Final Circuit

The output signal from VCO (Q1) passes through an RF amplifier (Q2, Q5, Q9) and drive amplifier (Q10, Q11), and is amplified by a power amplifier (Q12).

■Transmission/Reception Switching Circuit

The signal amplified by the power amplifier (Q12) passes through a transmission/reception switching circuit and a low- pass filter, and is fed to the antenna.

			Q12
Q11
Q10
			Q58
		VGG		VDD
Q15
5T
					IC2
				APC AMP
			1	AOUT	V+	8
R70	R71	R72	2	A–IN	BOUT	7
B			3	A+IN	B–IN	6
			4	GND	B+IN	5

Q13

B

The transmission/reception switching circuit consists of D10, L19, D12 and D13. These diodes are turned ON in transmit mode and OFF in receive mode to switch signals.

Q2

Q9

MIC IC5

IC16

Q1 RF AMP

RF AMP

HPF

MIC

VCO

AMP

Q5

VR5

MAX DEV

RF AMP

ANT

Q11

D10,L19

LPF

DRIVE AMP

D12,D13

ANT

SW

Q10

Q12

DRIVE AMP

POWER AMP

Fig. 6 Modulation, Drive, Final and

Transmission/reception switching circuit

■APC Circuit

The APC (Automatic Power Control) circuit is used to obtain a stable transmission power and controls transmission output by detecting the drain current of Q11 and Q12.

The transmission output can be changed in three levels: High, Mid, and Low.

The reference voltage is output from the BPF/APC terminal (pin 6) of the MPU (IC8) and the detection voltage generated by R70, R71 and R72 are fed to the APC differential amplifier (IC2).

The voltage in proportion to the difference between reference voltage and detection voltage is output from the BOUT terminal (pin 7) of IC2 as an APC voltage.

ANT

LPF

D10

L19

RX

D12 D13

Q55

Q14	TH1	–t
	+

		51
	7	THERM
		KAPC
6		BPF/APC	16
		FINAL
		IC8
		MPU

8

Fig. 7 APC and Temperature protection circuit