Motorola GM950E Service Manual page 46

Transmit Audio Circuits
The FLAT TX AUDIO signal from accessory connector U0400-5 is buffered by op-amp U0106-1 and
fed to the AFIC U0103-13 through gate U0107-1. Gate U0107-1 is controlled by the µP port PC7
(U0101-42) and selects between FLAT TX AUDIO or signalling signal created by the µP.
EXT MIC
FLAT TX
AUDIO
4.2 External Mic Path
The external microphone signal enters the radio on accessory connector J0400 pin 2 and connects
to the standard microphone input through R0421.
4.3 PTT Sensing and TX Audio Processing
Mic PTT is sensed by the µP U0101 pin 22. An external PTT can be generated by grounding pin 3
on the accessory connector if this input is programmed for PTT.
The MIC signal is routed to the AFIC (U0103) through R0146 and R0145 (4 channel radio) or
through op-amp buffer U0106-2 and option board connector J0103-3,1 (128 channel radio). R0145,
C0145, the ampliÞer inside the AFIC (pins 9,10) and gain setting resistor R0147 pre-emphasise the
MIC audio signal. After further limiting and Þltering the modulation signal emerges from the AFIC at
U0103-19/20. Both signals are weighted by resistors R0181, R0182 and add up to signal MOD IN.
4-8
J0101
J0103-3
9
MIC
CONTROL HEAD
CONNECTOR
J0400
2
5
ACCESSORY
CONNECTOR
Figure 4-1 Transmit Audio Paths
J0103-1
OUT
IN
OPTION
BOARD
10
FILTERS AND
PREEMPHASIS
ASFIC LIMITER
U0201
13
TX IN
SPLATTER
FILTER
21
TX OUT
4-BIT
14
DEVIATION
ATTENUATOR
5-BIT
15
DEVIATION
ATTENUATOR
19
TO
MOD IN
RF
SECTION
(SYNTHESIZER)
20
GEPD 5427
Theory of Operation