4.3.2 Transmitter Circuit
1) Microphone Amplifier Circuit
Voice signal from the microphone goes through pre-emphasis circuit consisting of C109,
R110 and operational amplifier IC103 - 1/2. The level of the signal is limited by the D101
and adjusted in the RV101 and amplified in the IC103 - 2/2. Then it goes through the
active 4-stage LPF consisting of IC102 etc., and modulated in the VCO unit ( VCO1).
2) High Frequency Power Amplifier Circuit
RF signal from the VCO unit (VCO1) goes through the 10dB attenuator consisting of R27 -
29 and will be amplified by Q6. Output from Q6 will amplify drive power necessary for the
FET power module (IC1) in the Q5. FET power module (IC1) will be amplified and the RF
signal will be output to the antenna switching circuit. RF output from the FET power
module (IC1) can be changed by changing the voltage of IC1 pin 2.
3) APC Circuit
Diode D3 is monitoring a part of the FET power module’s (IC1) output. The monitoring
signal will be output to IC101 via switching transistor Q1 and displays the “TX ON” on the
LCD. Voltage of monitoring signal will be compared and amplified between the set
standard voltage and IC2. Then the output voltage goes through buffer amplifier transistor
Q4 and will be connected to the pin 2 of FET power module (IC1) and make it a APC
control loop. Output power can be changed by controlling transistors Q2, Q3, and Q7 with
the CPU IC101 to change the set standard voltage.
4.3.3 Receiver Circuit
1) Antenna Switching Circuit
Signal received at the antenna connector J201 goes to high frequency amplifier circuit via
the 3 stage low pass filter consisting of coils L1-3.
2) High Frequency Amplifier Circuit
RF signal goes to the 1
st
mixer circuit through 2-stage BPF (consisting of coil L9, 10 and
L11, 12), and will be high frequency amplified by Q8 and then 2-stage BPF (consisting of
L14, 15 and L16, 17). The 1
st
image spurious frequency will be rejected to the adequate
level in the 4-stage BPF inside the high frequency amplifier circuit.
3) 1
st
Mixer Intermediate Frequency Amplifier Circuit
A single balanced mixer type consisting of transformer T1 and diode D5 is used in this
radio. The 1
st
IF signal from the mixer circuit goes to the 2
nd
mixer circuit through 2-stage
crystal filter (F1 and F2) and amplified in Q15 of the 1
st
IF amplifier circuit.
4) 2
nd
Intermediate Frequency Circuit
The 1
st
IF signal is added to IC201 and converted to 2
nd
IF signal. The 2
nd
IF signal goes
through FIL201 and amplified in the IC201 and then through FIL202 and the re-modulated
AF signal is output from IC201.
5) Low Frequency Circuit
