Multitone RPR 561, Technical Manual

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IC102
EEPROM
KEYPAD
LS101
IC107
AMPLIFIER
IC106
PRE-AMP
TR117,124
AGC
TR111-114
VOLUME
SWITCH
SQUELCH
GATE
TR119
TONE.Rx
TxDTMF
BEEP
µP
IC101
IC105
GATE
ARRAY
S103
LCD101
MODULE
LCD
ARDATA
RxAUDIO
DATA
`A'
`A'
D0-D3
BEC
S101
CANCEL
TAG10790-1
SQUELCH
IC106
PRE-AMP
MIC+
TR120,121
AGC
TR126
PRE-AMP
TR122
SP.EN
MIC.SIG
SPEECH3V
RPR 561
TM1200 Issue 1 Page 3 - 10
Figure 5: Decoder Board - Block Diagram
Receiver Audio Stages
39. 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.
40. 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.