TH-K2AT/K2E/K2ET
8
CIRCUIT DESCRIPTION
Transmitter System
■
M icrophone 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 w ill remove distortion outside the audio band.
■
M odulation Circuit
The audio signal amplified by the microphone amplifier
(IC16) passes t hrough a sem i-f ixed volum e (VR5) f or
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 pow er amplifier (Q12).
■
Transmission/ Reception Sw itching Circuit
The signal amplified by the pow er amplifier (Q12) passes
through a transmission/reception sw itching circuit and a low -
pass filter, and is fed to the antenna.
M IC
IC5
HPF
IC16
M IC AM P
Pre-
em phasis
Splatter
filter
VCO
Lim iter
6
1
Fig. 5 M icrophone amplifier circuit
M IC
HPF
M IC
AM P
IC16
ANT
SW
D10,L19
D12,D13
VCO
Q1
LPF
IC5
VR5
M AX DEV
Q2
RF AM P
Q5
RF AM P
Q9
RF AM P
Q10
DRIVE AM P
Q11
DRIVE AM P
Q12
POWER AM P
ANT
Fig. 6 M odulation, Drive, Final and
Transmission/ reception sw itching circuit
■
APC Circuit
The APC (Automatic Pow er Control) circuit is used to obtain
a stable transmission pow er and controls transmission output
by detecting the drain current of Q11 and Q12.
The transmission output can be changed in three levels:
High, M id, and Low .
The reference voltage is output from the BPF/APC terminal
(pin 6) of the M PU (IC8) and the detection voltage generated by
R70, R71 and R72 are fed to the APC differential amplifier (IC2).
The volt age in proport ion t o t he dif f erence bet w een
reference voltage and detection voltage is output from the
BOUT terminal (pin 7) of IC2 as an APC voltage.
Q10
Q15
Q11
Q12
VGG
Q58
VDD
LPF
ANT
D12
D13
RX
5T
B
1
AOUT
IC2
APC AM P
2
A–IN
3
A+IN
4
8
7
6
5
GND
V+
BOUT
B–IN
B+IN
R
72
R
71
R
70
Q14
B
Q13
+
TH1
–t
Q55
7
KAPC
51
6
BPF/APC
THERM
16
FINAL
IC8
M PU
D10
L19
Fig. 7 APC and Temperature protection circuit
The transmission/reception sw itching circuit consists of D10,
L19, D12 and D13. These diodes are turned ON in transmit
mode and OFF in receive mode to sw itch signals.
