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19. EXPLANATION OF BLOCK DIAGRAM
19.1. Audio Frequency Circuit and Control Circuit
Circuit Operation:
Transmission
2 types of voice input are provided: built-in microphone and optional external microphone. The
signal input through the microphone is amplified at the compressor (IC11), then connected to
the next circuit. In the next stage (IC13) the amplified signal is passed through the splatter filter
which limits the amplitude and band width. At the same time, CTCSS signal is generated and
added to the voice signal, then output to RF block as a modulated signal. VOX amplifier
amplifies the signal in its own route differently from the transmission voice circuit. It detects
the voice and send the output to CPU It detects the voice and sends the output to CPU through
IC14. In the scramble mode the scramble circuit reverses the frequency in IC11. (Reverse
Frequency 3.4 kHz)
Reception
The receiving voice is output by the demodulated signal (AF signal) from the RF block and
squelch signal. AF signal is amplified in IC13 and also the CTCSS signal is divided. The
detection signal of CTCSS is used for the mute control of signals. The output from IC13 is
processed in IC11 further and returned by the expander, then amplifies the power to drive the
speaker. (IC12: MAIN-SP/IC10: SUB-SP)
Control
The operation is controlled by CPU (IC17), LCD panel and control switch. Until running down
the battery, IC (IC8) and CPU (IC17) can work with little consumption current. (some
A) All of
other circuits are shut down by power supply IC (IC9) while the power is OFF, and they are
supplied the power from IC9 according to the control signal from CPU while the power ON. /
The vibrator motor is driven through the transistor (Q16) according to the port output of CPU. /
TX LED (red) is lighted by the power supply control (Q13) of transmission circuit on
transmitting. RX LED (green) is lighted by the output of Q19 on receiving.
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