Figure 7-2. Transmit Audio Paths - Motorola MCS 2000 Service Instructions Manual

7-18
.
J405
9
MIC
CONTROL HEAD
CONNECTOR
J403
13
23
EXT MIC
24
AUX TX
ACCESSORY
CONNECTOR
J401
14
AUX TX
INTERNAL OPTION
CONNECTOR
J408
14
AUX TX
INTERNAL OPTION
CONNECTOR
Inside the ASFIC, the mic audio is filtered to eliminate components outside the 300-3000 Hz voice
band, and pre-emphasized if pre-emphasis is enabled. The capacitor between ASFIC pre-emphasis
out U0200-C8 and ASFIC limiter in U0200-E8 AC couples the signal between ASFIC blocks and
prevents the DC bias at the ASFIC output U0200-H8 from shifting when the ASFIC transmit circuits
are powered up. The signal is then limited to prevent the transmitter from over deviating. The limited
mic audio is then routed through a summer, used to add in signalling data, and then to a splatter filter
to eliminate high frequency spectral components that could be generated by the limiter. The audio is
then routed to two attenuators, which are tuned in the factory or the field to set the proper amount of
FM deviation. The TX audio emerges from the ASFIC at U0200-H8 AUDIO MOD, at which point it is
routed to the RF section.
Auxiliary TX Audio Paths
There are three auxiliary transmit audio inputs that are routed to the auxiliary transmit path in the
ASFIC. These are AUX TX IN1, AUX TX IN2, and AUX TX IN3. The 3 paths, only one of which can
be active at a time, are buffered by U0202.
December 6, 2004
Controller Section Theory of Operation: Audio and Signalling Circuits
D3
HPF
A6
MIC AMP OUT
B8
MIC IN
ASFIC
EXT MIC IN
A7
U0200
LS SUMMER
SPLATTER
FILTER
AUX TX IN
D7
HS SUMMER
LIMITER
PRE EMP OUT
C8

Figure 7-2. Transmit Audio Paths

COMP BUF IN
HEARCLEAR - I
IC
U0250
COMP OUT
F3
C7
TX IN
FILTERS AND
PREEMPHASIS
H8
VCO ATN AUDIO MOD
ATTENUATOR
LIM IN
E8
TO
RF
SECTION
(VCO)
68P81083C20-D