Motorola GM950E User Manual

Receive Audio Circuits
6.3-12 Theory of Operation
6.0 Receive Audio Circuits
Refer to Figure 6.3-3 for reference for the following sections.
Figure 6.3-3 Receive Audio Paths.
6.1 Squelch Detect
The IF IC controls the squelch characteristics of the radio. With a few external parts (R5222, C5229,
C5230, R5223) the squelch tail, hysteresis, attack and delay are optimized for the radio. To set the
squelch threshold the signal from IF IC pin 23 (line SQ ATT IN) is routed to the squelch attenuator
input of the AFIC (U0103-16). The attenuated signal (line SQ ATT OUT) from the AFIC (U0103-18)
enters the IF IC at pin 20 and is used to create a squelch indicator signal available at pin 15 (line
CSQ DET).
The microprocessor controlled ADAPT signal at pin 22 activates the fast squelch indicator signal at
IF IC pin 18 (FAST SQ). Both squelch indicator signals CSQ DET (pin 15) and FAST SQ (pin 18) are
combined, weighted by resistors R0111 / R0112 and fed to one of the microprocessor´s ADCs
(U0101-15) for interpretation. From the voltage weighted by the resistors the µP determines whether
CSQ DET, FAST SQ or both are active.
J0400
11
16
1
FLT RX AUDIO
EXTERNAL
SPEAKER
INTERNAL
SPEAKER
ACCESSORY
CONNECTOR
CONTROL
HEAD
CONNECTOR
HANDSET
AUDIO
14
1
2
J0101
INT
SPKR-
SPKR +
SPKR -
1
9
ATTEN.
J0103-2
6
8
7
J0103-4
J0103-5
DET AUDIO
(DISCRIMINATOR
AUDIO)
GEPD 5429-1
16
23
22
INT
SPKR+
4
6
AUX
RX IN
PL IN
SQ IN
AFIC
U0103
AUDIO
PA
U0401
IN 2
OPTION
BOARD
IN 1
OUT
VOLUME
ATTEN.
FILTER AND
DEEMPHASIS
18
28
MICRO CONTROLLER
U0101
15
CSQ DET
CSQ DET
FAST SQ
15
18
23
20
IF IC
DET AUDIO
SQ LIM OUT
SQ RECT IN
SQUELCH ATTENUATOR
SQ OUT
UNAT
RX OUT
RX AUD OUT
RX IN
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Motorola GM950E Specifications

General

Brand	Motorola
Model	GM950E
Category	Radio
Language	English