Ericsson EDACS Monogram Series, Руководство по обслуживанию

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AE/LZB119 1647 R1A
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Transmit Audio Paths
The microphone receives a dc bias through R315. Mic
audio is coupled into U804 pin 74 via J901 pin 3, U604.B,
and C303. In the ASP, Microphone. audio passes through
an audio switch (MIS) to the microphone amplifier. A
second switch in the Mic. amp circuit (MGS) sets the gain of
the Mic. amp. This switch is normally closed for low Mic.
gain. The audio from the Mic. amp is the pre-emphasized
and 300 Hz high-pass filtered. The Mic. audio then leaves
the ASP on U804 pin 70.
Pre-emphasized Mic. audio is coupled into U804 pin 57
by C304. The audio is passed through muting switch (AEN)
and then it feeds the limiter circuit. This limiters threshold
can be stepped up by the micro controller so peak deviation
of the Mic. audio can be increased when Channel Guard is
not present.
Limited Mic. audio then passes through the summing
amp in the ASP which sums the Mic. audio, tones, and data.
The output of the summing amp feeds a switch (PBY) that
switches the Mic. audio to the 3 kHz post limiter filter (for
limited Mic. audio) or directly to the transmit deviation level
control circuit in the ASP for data transmissions. The output
of the digital deviation control passes to the output on U804
pin 60.
The TX audio output feeds U301.A. This circuit
provides a gain of two for any voice, tone, or data that is to
be transmitted. C308 and R310 provide a low-pass
characteristic that begins to roll-off at approximately 10
kHz. U301.A also serves to invert transmit data before it is
applied to the modulating circuitry on the RF Board.
High-Speed Data Encoding
When the radio is transmitting high-speed data, the
serial data from the modem is applied to U804 pin 80.
Inside the ASP, this data passes through a Bessel filter and
then the output of the filter is sent to the TX summing
amplifier. The output of the summing amp feeds an audio
switch (PBY) to allow 3 kHz post limiter filter bypassing
during data transmissions. The data then passes through the
digital deviation control and through an audio switch (TXO)
output U804 pin 60 to feed U301.A and modulating
circuitry.
During high-speed data transmissions, the modem input
from the receive data limiter requires muting to prevent the
modem from being disturbed by excessive receiver noise.
Micro controller U701 pin 7 switches low during transmit to
clamp the line to ground.
CG Tones And Low-Speed Data Encoding
Micro controller U701 generates the low-frequency
Channel Guard tones and low-speed data using its WB1 and
WB2 Walsh bit outputs. These two bits are also used to
generate GE-MARC signaling tones as described in the
following section entitled "GE-MARC SIGNALING TONE
ENCODING".
The 2-bit low-frequency Walsh bits are summed into
the ASP at U804 pin 38. These stepped tones or data, pass
through an audio switch (TX) in the ASP and then the
105/210 Hz low-pass filter. Cutoff for this filter is switched
to 105 Hz when the programmed CG encode tone is equal to
or less than 105 Hz. The filter is switched to a cutoff at 210
Hz if the programmed CG encode tone is greater than 105
Hz or if the radio is in the data encode mode.
The filtered tones/data, pass through a gate (CGE) and
then out of the ASP at U804 pin 37, through R317 via the
TX CG line, and back into the ASP on U804 pin 58 (CGIN).
GE-MARC busy tones are also fed into this pin through
C310.
In the ASP, the filtered tones/data pass from U804 pin
58 (CGIN) through an audio switch (BEN) to feed the
transmit summing amplifier. The output of the summing
amp feeds another switch (PBY) that switches the 3 kHz
post limiter filter in-line. The output of the post limiter
passes through the digital deviation control, through another
switch (TXO), and then out of the ASP to U301.A. See
section entitled "TRANSMIT AUDIO PATHS" for details
on U301.A.
GE-MARC Signaling Tone Encoding
Micro controller U701 generates the GE-MARC
signaling tones using its WB1 and WB2 Walsh bit outputs.
These two bits are also used to generate Channel Guard
tones and low-speed data as described in the previous
section entitled "CG TONES AND LOW-SPEED DATA
ENCODING".
The 2-bit generated GE-MARC tones feed U804 pin 59.
In the ASP, the tones pass through audio switch (DEN) and
the summing amplifier in the TX audio path. The tones are
next routed to the 3kHz post limiter filter, through another
audio switch (PBY). They are then filtered, sent through the
digital deviation control, audio switch (TXO), and then out
of the ASP on U804 pin 60.
GE-MARC Busy Tone Encoding
Micro controller U701 pin 27 generates either the
standard 3052 Hz or the alternate 2918 Hz busy tone. This
square wave signal is summed into the TX audio path at the
same point as low-frequency CG tones/data at U804 pin 58
(CGIN). C752, R753, and R316 determine the 1kHz
deviation level. C310 couples the tone into U804 pin 58.