Kenwood TM-V7A Service Manual page 16

TM-V7A/E
16
CIRCUIT DESCRIPTION
Mic Amp Circuit
The audio signals from the microphone are impedance
matched and enter AK2343 (IC507). AK2343 comprises a
2-stage amp, mute circuit, band pass filter circuit, limiter
circuit, and splatter filter circuit. It provides the audio signal
amplification. and preemphasis characteristic. The mute
circuit is used while transmitting DTMF signals and the like
from the microprocessor and during data transmission from
the packet terminal. The modulation circuits are directly
connected with the VCO variable-capacity diode for both
the 144MHz band and the 430MHz band and apply
frequency modulation.
Fig.14 Mic amp circuit (1C507:AK2343)
Microphone Key Input
The microphone UP/DOWN and function keys are con-
nected to the microprocessor analog input. The voltage
when a key is ON operates the corresponding function.
Also, the key input interrupt circuit is for switching the power
ON/OFF with the microphone. When the DOWN, MR, and
PF keys are pressed, an interrupt is generated and the mi-
croprocessor is awoken from stop mode. However, with the
TM-V7A/E, the power key is on the microphone, so the set
is designed to switch on the main unit power only when the
PF key is pressed and other interrupts are ignored.
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Fig.15 Microphone key input circuit