Motorola MSF 5000 Instruction Manual page 52

Chapter 1 Description
MSF
5000
Instruction Manual
SSCB
Functional Description
1-14
The output signal of
the
audio gate circuits is routed
to the
Private Line
(PL)
low-pass filter circuits which filters out unwanted low frequency audio
components.
The filtered signal is input
to
EEPOT
5 (RX
level adjust)
to adjust the
level of
receive audio for use throughout the station.
The output is the final output of the receive audio processing circuitry (RX1
AUDIO). If
the station is properly aligned, during normal operation, an
RF
signal
at 60% deviation
of
a
1
kHz
tone
applied
to the receiver should result
in
an RX1
AUDIO level of
about 350mV rms at TP1 of the SSCB.
Transmit Audio Processing
The transmit audio processing circuitry performs various functions on the
transmit audio signal before
it
is sent to the modulator.
This circuitry
contains
several inputs that originate from the
SSCB audio routing
circuitry. Refer to
Figure
1-6
for
a
block diagram of
the transmit audio processing circuitry.
For
900
MHz
stations, the transmit audio signal is compressed, gated, and routed
through
a
pre-emphasis and limiter circuit, summed (SUMMED
TX
AUDIO),
and
filtered
by
a
low-pass splatter
filter.
The output of
the splatter
filter is routed
to the
maximum deviation adjust circuit.
The PL ENCODE AUDIO from
the PL/connect tone encoder is also sent to the
maximum deviation adjust circuit.
This
circuit contains
EEPOT
4
(maximum
deviation level), adjusted
to
limit maximum transmit deviation to reduce
over-deviation. The adjusted level must
be set
while incorporating
PL/DPL
codes, failsoft codeword, connect tone,
etc.
The
FCC
and system design
requirements must also be considered.
Other audio signals are also
input
to the
final output stage of the transmit audio
processing circuitry. Refer to the
Audio Routing
section for additional information
on these signals.
The final output of the transmit audio processing circuitry is
TX
MOD AUDIO.
This signal
is sent directly to the modulator
within
the transmitter before
transmitted and amplified.
Tone Generating
The SSCB
generates
various
tones
for different purposes. The
tones are:
©
Transmit audio alarm
tones
-
audible alarms sent over the air during
a
specific failure (refer to Chapter
2
- Operation)
0
PL/DPL-
Private
Line/Digital
Private Line for
use
in
conventional stations
©
Failsoft codeword
-
connect tone used
in Trunked
systems and is sent when
the station enters the
Failsoft
mode
©
Connect tone
-
used
in Trunked
systems
68P81092E02
3/19/94
Connect