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some wildcard applications. The cabling to these connec-
tors are interchangeable.
13207,
13208,
and J3209 are the IPA Forward, IPA Re-
verse, and Driver Forward Power connectors, respective-
ly. The IPA Forward Power and IPA Reverse Power sig-
nals are routed from the IPAoutput via a wattmeter(stan-
dard on data stations). The Driver Forward Power signal,
in driver-equipped radios, comes from the driver power
control connector.
4.7
DATA AND DIAGNOSTICS OPERATION
RECEIVE AUDIO ROUTING - Discriminator
1
Au-
dio (Quad!) or Diversity Audio is selected via the U3232B
analog switch. The audio signal is unfiltered, and buff-
ered by voltage follower U3239A and output to the out-
side world at P3203-15.
TRANSMIT AUDIO ROUTING- Thmsmit data is in-
put to SAM at P3203-17. It is buffered by U3200B but
otherwise unprocessed. It is then
passed through analog
gate U3202B which selects between BSC transmit data
and signaling encoder audio, and then through U3202A
which can be programmed to provide a data mute func-
tion. This resultant signal then is routed to the station
control board where it is summed with other transmit
modulation audio, and routed to the VCO. For data oper-
ation, JU14 must be in the NORM position and JU6 must
be ALTposition on the Station Control Board in order for
the BSC transmit data to bypass the splatter filter and
limiter circuitcy.
INPUT CONFIGURATION -
Control inputs to the
data station
vary
depending on which station controller is
being used. Code plug programming can be viewed and/
or modified using the RSS. See the RSS manual for fur-
ther information on programming the inputs. For Fast
Key Up, JU19 on the station control board must be in the
NORM position, and proper programming on both the
SAM and station control is required.
OUTPUT CONFIGURATION- Status/ Alarm outputs
from the data station vacy depending on which station
controller is being used. Code plug programming can be
viewed and/or modified using the RSS. See the RSS man-
ual for further information on programming the outputs.
4.8
SIGNALING OPERATION
The SAM board implements three signaling decoders:
Stat-Alert
(MDC1200),
Single-1bne/Select5,
and
DTMF. Due to microprocessor loading, the Stat-Alert
and Single-1bne/Select5 decoders can not be enabled si-
multaneously for a given mode.
A system of analog gates on the SAM allows either Quadl
Audio, Diversity Audio, Quad2 Audio, or Wireline
'Itans-
mit Audio to feed any of the three signaling decoders on
the SAM board. Of course, each decoder can look at only
one audio source at a time; the decode source is mode-de-
pendent.
The SAM also supports encode of all three signaling
types. However, the SAM is half-duplex only- that is, it
cannot decode while an encode is in process. The encode
signaling may be routed to either the wireline or transmit·
ter or both. The encode level is controlled by an EEPOT
which may be
accessed
from the front panel (as poten-
tiometer number F) or from the freld programmer.
RECEIVE AUDIO ROUTING - U3201A, B, and C
and U3232A, B, and C are transmission Gates, each of
which acts as a single-pole double-throw .switch to select
which audio is used by each of the three SAM decoders.
The audio selected is either Quadl Audio, Diversity Au-
dio, Quad2 Audio, or Wireline Thmsmit Audio.
TONE DECODER -'Ibne decoding on the SAM board
is done in software. Before decoding. audio processing of
the received signal is done by a bandpass filter consisting
of operational amplifiers U3237 A, B and U3238A, B, and
limiter U32U. The processed audio is then fed to input
capture port PAl on the microprocessor (U3203-33).
The bandpass fllter is three-stage, ten-pole fllter, with 3
dB
comers at approximately
250
Hz and
2900
Hz. This
filter cleans up the received signal by removing frequency
components which are outside the range of the tones to
be decoded. The limiter takes the filtered sine wave and
creates a square wave of the same frequency for input to
the microprocessor.
TROUBLESHOOTING- When a carrier is modulated
with a continuous tone and fed to the station receiver, and
therefore to the SAM board, there should be a square
wave at pin
1
ofU3212. H that is not the case, check to
see
if there is a sine wave at U3237-1 and U3237-7.
BINARY DECODER -
Binal)' decoding must be
thought of as a two step process. The flrst step is demodu-
lating, or determining what bits have been received. The
second step is decoding, or determining what the bits
mean. The SAM board implements both steps in soft-
ware.
1b determine what bits have been received, the SAM uses
a software demodulator which uses the same micropro-
cessor input pin as the tone decoder. This input is used
to generate a clock signal at the output compare port at
U3203-28. This clock drives the D-Flip-Flop, U3236, the
output of which is then fed to the PA7 input port at
U3203-27 via analog gate U3232C. Because the binal)'
signaling used is in 1200 baud frequency shift keying for-
mat, where a logical "1" is represented by a full cycle of
1200 Hz and a logical
"0"
is represented by one and one
half cycles of 1800 Hz, the software demodulator per-
forms as a specialized tone decoder which translates 1200
and 1800 Hz tones (input to the J,LP at U3203-33 and
U3203-27) into l's and O's. The resulting bit stream is de-
coded by the microprocessor. As each bit comes the mi-
4
68P81087E72
6/30193
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