3.4.3 APC Circuit
Diode D4 is monitoring a part of the power module’s(IC5) output. The monitoring
signal will be output to IC5 via switching transistor Q8 and display the “TX ON” and
the LCD.
The output voltage from IC5 controls the RF power to keep the RF output at a
constant level.
3.4.4 DSC Signal Treatment
In DSC mode at CH70,a sequence signal from CPU is input to MODEM IC(IC11) and
converted to an analog signal. As a MODEM TX signal,this signal switches the analog
switch(Q20) from microphone input position to DSC position. Then DSC signal is sent
out to the transmitter microphone amplifier.
If NMEA information are input to P501 connector through GPS or other devices
connected to it,these information are taken into CPU through photo-coupler of Q22
and can be transmitted with DSC to provide information such as position and time.
3.5 RECEIVER CIRCUIT
3.5.1 Antenna Switching Circuit
A signal received at the antenna connector J501 goes to high frequency amplifier circuit via
4-stage low pass filter consisting of coils L1-L3 and L21.
3.5.2 High Frequency Amplifier Circuit
RF signal goes to the 1
st
mixer circuit through 2-stage BPF(consisting of coil L5,6) and will be
high frequency amplified by Q1 and then 3-stage BPF(consisting of L8,L10,and T3) . The 1
st
image spurious frequency will be rejected to the adequate level in the 5-stage BPF inside the
high frequency amplifier circuit.
3.5.3 1
st
Intermediate Frequency Amplifier Circuit.
A double balanced mixer(DBM) of IC1 is used for 1
st
mixer of Receiver.
RF signal from RF Amplifier circuit input to IC1 pin 6. Receiver local frequency input from PLL
IC(IC2) pin 20 to IC1 pin3 and then converts the frequency.
The converted 1
st
IF signal(the frequency of 1
st
IF is 21.7MHz) goes through 1-stage crystal
filter(F1) and is amplified in transistor(Q2)
