Table of Contents
Advertisement
Chapter
1
Description
MSF
5000
Instruction Manual
TTRC
Audio Board
TRC
Decode Audio
Activity
Detector
The main function of
the
activity
detector is to support
LLGT
detection.
The input
to the
activity
detector
is
ALC
audio (TP5) which first
passes through a bandpass
filter.
The bandpass filter is followed by
a
comparator combination.
If
the
signal
entering
the
activity
detector is greater than or equal to -15 dBm at approximately
1900
Hz,
the
ALC
output is considered activity
by
the circuit.
This voltage level is
read
by
the microprocessor on the
TTRC
Logic
board to detect the presence of the
LLGT
audio activity.
Transmit Notch Filter
Audio
from the
TX
audio level adjust circuit is also
sent to the transmit notch filter
hybrid.
Only
one
of
the
two
filters on the
hybrid
is being used
in
the
transmit
audio path,
the second
filter is in
the receive
audio path. This filter notches out
the
Guard Tone
(GT)
frequency
area
of
the
voice spectrum
before
it is
transmitted.
The transmit notch filter may
be removed from the transmit audio path for special
applications, such
as
simulcast,
by placing
JU4204 for transmit audio and JU4203
for
wireline transmit audio in
the alternate position.
For
other applications,
transmit audio can be summed into inverting amplifier (Line
2
Sum
or
Line
4
Sum)
via
the transmit notch filter and a line
shaping
filter.
Jumpers JU4228 (Line
2
output level), and JU4229 (Line
4
output level)
are used to
center
EEPOT
C
and
D
around
0 or -10
dBm depending on their position. The
notch filter can also be removed from this path
by placing
JU4203 in
the alternate
position.
The
TRC
decode audio is directed to the
ALC
circuit. The output of
the
ALC
circuit is
sent to the tone processing circuit, the interface for tone
decoding
between the analog decode audio section and
the microprocessor.
The
TRC
decode audio circuit is responsible for bandpass filtering and
limiting
the
audio
signal
before
passing it
to the microprocessor on the
TTRC
Logic
board for tone
detection.
Figure
1-12
shows
a
block diagram of
the
TRC
decode audio circuitry.
TP3
TRC
DECODE
DECODE
AUDIO
AUDIO
TONE
»
PROCESSING
CIRCUITRY
MSFI065
020794JNM
Figure 1-12
TRC
Decode Audio Circultry
1-30
68P81092E02
3/19/94
Chapter
1
Description
MSF
5000
Instruction Manual
TTRC
Audio Board
TRC
Decode Audio
Activity
Detector
The main function of
the
activity
detector is to support
LLGT
detection.
The input
to the
activity
detector
is
ALC
audio (TP5) which first
passes through a bandpass
filter.
The bandpass filter is followed by
a
comparator combination.
If
the
signal
entering
the
activity
detector is greater than or equal to -15 dBm at approximately
1900
Hz,
the
ALC
output is considered activity
by
the circuit.
This voltage level is
read
by
the microprocessor on the
TTRC
Logic
board to detect the presence of the
LLGT
audio activity.
Transmit Notch Filter
Audio
from the
TX
audio level adjust circuit is also
sent to the transmit notch filter
hybrid.
Only
one
of
the
two
filters on the
hybrid
is being used
in
the
transmit
audio path,
the second
filter is in
the receive
audio path. This filter notches out
the
Guard Tone
(GT)
frequency
area
of
the
voice spectrum
before
it is
transmitted.
The transmit notch filter may
be removed from the transmit audio path for special
applications, such
as
simulcast,
by placing
JU4204 for transmit audio and JU4203
for
wireline transmit audio in
the alternate position.
For
other applications,
transmit audio can be summed into inverting amplifier (Line
2
Sum
or
Line
4
Sum)
via
the transmit notch filter and a line
shaping
filter.
Jumpers JU4228 (Line
2
output level), and JU4229 (Line
4
output level)
are used to
center
EEPOT
C
and
D
around
0 or -10
dBm depending on their position. The
notch filter can also be removed from this path
by placing
JU4203 in
the alternate
position.
The
TRC
decode audio is directed to the
ALC
circuit. The output of
the
ALC
circuit is
sent to the tone processing circuit, the interface for tone
decoding
between the analog decode audio section and
the microprocessor.
The
TRC
decode audio circuit is responsible for bandpass filtering and
limiting
the
audio
signal
before
passing it
to the microprocessor on the
TTRC
Logic
board for tone
detection.
Figure
1-12
shows
a
block diagram of
the
TRC
decode audio circuitry.
TP3
TRC
DECODE
DECODE
AUDIO
AUDIO
TONE
»
PROCESSING
CIRCUITRY
MSFI065
020794JNM
Figure 1-12
TRC
Decode Audio Circultry
1-30
68P81092E02
3/19/94
Advertisement
Table of Contents
