Receive Audio Circuits; Squelch Detect - Motorola GM-950 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).
5C.3-14
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
Theory of Operation