Receive Audio Circuits; Squelch Detect - Motorola GM1200E Service Manual

Receive Audio Circuits

6.0 Receive Audio Circuits
Refer to Figure 3-3 for reference for the following sections.
OPTION
BOARD
FROM
RF
SECTION
(IF IC)
6.1

Squelch Detect

The radio's RF circuits are constantly producing an output at the discriminator U5201-28 (UHF) /
U5201-28 (VHF) / U2201-28 (MB). This signal (DET AUDIO) is routed to the ASFIC's squelch detect
circuitry input SQ IN (U0201-H7). All of the squelch detect circuitry is contained within the ASFIC.
Therefore from a user's point of view, DET AUDIO enters the ASFIC, and the ASFIC produces two
CMOS logic outputs based on the result. They are CH ACT (U0201-H2) and SQ DET (U0201-H1).
The squelch signal entering the ASFIC is amplified, filtered, attenuated, and rectified. It is then sent
to a comparator to produce an active high signal on CH ACT. A squelch tail circuit is used to produce
SQ DET (U0201-H1) from CH ACT. The state of CH ACT and SQ DET is high (logic 1) when carrier
is detected, otherwise low (logic 0).
3.1-14
B2
UNIV IO
UNAT RX OUT
H5
J0103-4
IN 2
J5
EXP AUDIO IN
J0103-2
H6
RX IN
OUT
IN 1
J0103-5
J6 AUX RX IN
J7 PL IN
DET AUDIO
(DISCRIMINATOR AUDIO)
Version before 0102726B09 PIN no is 25
*
Version 0102726B09/10 PIN no is 40
Figure 3-3 Receive Audio Paths.
1
AUDIO
4 SPKR +
PA
SPKR -
U0401
6
9
INT
SPKR+
ATTEN.
J4
RX AUD OUT
VOLUME
ASFIC
ATTEN.
U0201
FILTER AND
DEEMPHASIS
PL FILTER
LIMITER
LIMITER, RECTIFIER SQUELCH
FILTER, COMPARATOR CIRCUIT
SQ DET
SQ IN CH ACT
H2
H7
*
MICRO
CONTROLLER
U0101
ACCESSORY
CONNECTOR
11
FLT RX AUDIO
J0400
16
EXTERNAL
1
SPEAKER
INT
SPKR-
CONTROL
HEAD
CONNECTOR
2
INTERNAL
1
SPEAKER
J0101
14
HANDSET
AUDIO
PL
A4
LIM
H1
43
10
GEPD 5428-2
GEPD5428-2
Introduction/Theory of Operation