2) Transmitter System
1. Modulation Circuit
3) PLL Circuit
The microphone amplifier IC1 (IDC, LPF) consists of two operational amplifi-
ers. The signal from the microphone is led to pre-emphasis circuit consisting
of C36 and R47 and then to the limiter circuit. The limiter circuit uses the
saturation of the OP amplifier. The amplified signal is input to the low-pass
filter IC1A. The output signal from the microphone amplifier is passed
through variable resistors VR2 for modulatlon adjustment and input to the
VCO unit. Sub tone deviation is determined by R24, R25 and VR2. The
radio does not have the adjustment variable resistor for sub tone deviation.
2. TX Amp. Circuit
The signal from VCO is ampriied by TX, RX wide band LO amplifier Q19.
The signal from Ql9 is passed through the transmission/reception selector,
and amplified byQ20 and Q15. The PA unit is driven at 200mW driving
power.
3. PA Circuit
IC5 is 50W powered amplifier module. The output power is controlled by
the voltage ofV1. The RF signal amplified 50W in PA is passed through D3
and three-stage transmission/reception low-pass filter, and input to the
antenna connector.
4. ALC Circuit
The power detection circuit consisting of D17 and D18 rectifies the output
signal voltage. The detected DC voltage is led to the VR1 (power adjust
trimmer), and amplified by Q3, Q9 and Ql3. Output power is controlled by
voltage of V1 in lC5 and collector voltage of Ql5. When the temperature
goes up unusually, the power down circuit consisting of R101 and TH2
works to prevent the device from the destruction.
The VCO unit is designed for the PLL circuit, putting the VCO on one side,
and PLL circuit on the other side.
Q301 in the VCO is grounded using the gate oscmator, and its frequency
covers 134MHz to 174MHz without transmission/reception shift circuit.
lC301 is pulse swallow system based PLL IC with the built-in prescaler,
which synthesizes 150MHzlband signal.
The loop filter consisting of Q302 and Q303 is the active type.
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