Multitone RPR 563GS, Technical Manual

Page: 39 / 87

RPR 563GS/KGS
TM1187A Issue C Page 3 - 9
Receiver Audio Stages
34. Receiver audio (RXAUDIO) from the Radio Board is applied to SK101 pin 3 and fed
through the squelch gate transistor TR119 which is controlled by the decoder squelch
output. If valid audio is received then the transistor conducts and the signal is passed
to pin 7 of pre-amplifier IC106. Output from IC106 pin 1 is passed to D106, TR124 and
TR117 which form an AGC circuit, and to IC107 which amplifies the signal to drive
loudspeaker LS101. Amplifiers IC106 and IC107 operate only when SPEECH3V is
present.
35. Control of loudspeaker volume is achieved by an electronically-controlled potentiometer
comprising R171, and transistor-switched resistors R135, R137, R139 and R141.
Transistors TR111-TR114 which provide the potentiometer switching, are controlled by
microprocessor IC101.
Microphone Audio Stages
36. Audio from the microphone is fed via C137 to IC106 at pin 6. It is then amplified and
fast AGC-limited by IC106, D105, TR120 and TR121 to give a maximum level of 1.2V
peak-to-peak. Microphone audio is then output at SK101 pin 8 to the Radio Board.
Decoder
37. The decoder circuits comprise Gate Array IC105, microprocessor IC101, EEPROM
IC102 and associated components.
38. Microprocessor IC101 carries out the decoding and control functions of the transceiver.
Its functions include:
a) DTMF tone generation from a built-in encoder. Output is presented at pin 47.
b) Scans the keypad to determine which key has been pressed.
c) Drives the display module.
d) Switches the LCD and keypad backlighting on and off.
e) Controls the /TxKEY and /SQUELCH lines.
39. The LCD module is controlled directly from IC101. The icon is driven from IC101 via
TR115, C119 and C118. Power to the display is provided via TR108 which is gated by
IC101. Backlighting for the display and keypad is controlled by TR107 gated by IC101.