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croprocessor performs its decoding function, attempting
to decode the bit pattern which has been demodulated
into a
valid
received message.
BINARY ENCODER- When encoding, the binary mo-
dem IC (U3207) will take digital1's and O's from the mi-
croprocessor (input to the modem at U3207-15) and
translates them into 1200 and 1800Hz tones (output from
the modem at U3207-6). The resulting output is then
summed into the summing op-amplifier U3200D.
DTMF
DECODER - The SAM DTMF decoder uses
a specialized IC to do the translation from audio signals
to digital signals. U3208 decodes the
DTMF
audio se-
quence and provides a four-bit nibble to the microproces-
sor specifying which of the 16 possible tone pairs was re-
ceived.
TONEIDTMF ENCODER - Both of these signaling
types are encoded on the SAM board
by
an 8-bit digital-
to-analog converter (DAC) implemented as an R/2R lad-
der around op amp U3200A A three-pole low-pass
smoothing filter formed
by
U3200C follows the DAC.
TRANSMIT AUDIO ROUTING- Both the binary en-
code
signal
from the modem IC U3207 and the tone and
DTMF
signals from the DAC are summed
by
U3200-14.
Variable
gain
is set
by
EEPOT U3209.
The output of the summer stage is fed to both analog
gates U3202-13 and U3202-5.
These gates control
whether the encode audio will be passed to RAC Line Au-
dio or RAC GCC Data Audio, or both. The RAC Line
Audio signal feeds to the Line Summer stage on the Sta-
tion Control Board (this requires jumper 1U17 on SSCB
to be in ALT position). The RAC GCC Data Audio line
feeds to the splatter filter on the Station Control Board.
Note that when encoding RAC tones or sequences, the
jumpers on the Station Control Board must be set such
that they go through the splatter filter, that
is,
1Ul4 in
ALT position, and 1U6 in NORM position.
ENCODER TROUBLESHOOTING -
The SAM
board will automatically encode a 1200Hz
signal
when the
SAM EEPOT (#F displayed on the front panel) is se-
lected.
A sine wave should be visible at U3200-1,
U3200-8, and U3200-14. The amplitude of the signal at
U3200-14 is adjusted
by
EEPOT U3209. The EEPOT
should be adjusted to verify that the amplitude does
change. H the
signal
is not present at any of these points.
supply voltages should be checked, as well as a defective
EEPOT.
5. LEVEL SETTING
Most of the level setting potentiometers in the Data sta-
tion control tmy are digitally controlled, solid state non-
volatile potentiometers referred to as EEPO'IS. These
EEP01S can be manipulated
by
using the Field Progmm-
mer or through a front panel switch toggling sequence.
Before setting SAM encode levels, the station Max Devi-
ation EEPOT must
already
be set correctly.
Also,
if en-
coding to the wireline, the Line21Une4 Level EEPOT
must
already
be set correctly. After aligning the station
according to the
instructions
given in the
User
Manual,
use the following procedure set EEPOT IF {the SAM en-
code level potentiometer):
Step 1. Verify that
all
front panel switches are in their
normal positions. The station should not be in PL DIS-
ABLE or ACCESS DISABLE.
Step
2.
Hold the SElECT/SET switch in the SET posi-
tion, and then move the PL DISIXMIT switch to the PL
DIS position. Be sure to move
and
hold the SET switch
before the PLDIS switch. While both switches are active,
three
digits on the front panel STATUS display will show
EEP.
Step 3. Release the SET switch, and then return the PL
DIS switch to the normal position. After a few seconds,
the leftmost digit of the STATUS display will show a 0
which represents the EEPOT number in hexadecimal
(0
through hex
F).
The other
two
digits will show a decimal
value from 00 to 99 which represents the current wiper
position of the EEPOT.
Step 4. Thggle the SELECT/SET switch to the SELECT
position. A decimal point on the display will light. Thggle
the switch again to move the decimal point from one digit
to another. Set the decimal point to the leftmost digit.
Now toggle the switch to the SET position. Thggling to
the SET position scans the current settings of the EEP-
018. A delay between toggles of more
than
fwe seconds
times out the decimal point. Th bring the decimal point
back, toggle to the SELECT position. However, if the
SET position
is
toggled after the decimal point times out,
the display will exit the EEPOT setting mode and revert
to normal opemtion. Th re-enter the EEPOT mode, re-
turn to Step
1.
Step S. Select EEPOT #F. When you do this the SAM
board will encode a 1200Hz tone. Move the decimal point
to the next (tens) digit. Thggle to the SET position while
monitoring the output you are trying to adjust. Thggling
the switch to the SET position will increment the current
digit
by
1. If the SAM
is
encoding to the transmitter, hold
the PL Dis/Xmit switch down (in the Xmit position) and
monitor the 'Il:ansmit Deviation while adjusting the EEP-
OT. If the SAM is encoding to the wireline, monitor the
wireline level while adjusting the EEPOT. When the out-
put gets close to the required level, move the decimal
point to the third (ones) digit, and fine tune to there-
quired level. H you overshoot the required level, scroll
the wiper through position 99, and
try
again. The EEP-
018 can be adjusted only in one direction from the front
panel. When using the field progmmmer's alignment
screens, the EEP01S may be adjusted in either direction.
6/30193
68P81087E72
s
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