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SLM-7650 Satellite Modem
Theory of Operation
The IESS documents define the content of the bits within the overhead frame commonly
referred to as Engineering Service Channel (ESC) data. The modem does not provide
access to ESC data but sets all of the bits in a 'non-inserted' state so there is no problem
interfacing into an open network earth station. An optional interface card is available to
provide the interface to the IESS defined ESC data.
The modem is able to provide a bit error rate if the demodulator receives a 2047 pattern
and the demodulator test mode of 2047 is turned ON. The modulator is also capable of
substituting the 2047 test pattern in lieu of the incoming data stream. The 2047 test
pattern is a standard test pattern compatible with the FIREBERD 6000 and similar
commercial BER testers. In additional to the 2047 test pattern, a special MIL test pattern
is available. This MIL pattern is a modified 2047 pattern that pads the eleven 0s in a
2047 pattern to 50 (2086) once every five, 2047 patterns. This creates a 10274-bit test
pattern. This MIL test pattern must be turned on in the modulator for and BER results to
be displayed.
The receive baseband section contains a configurable FIFO buffer large enough to handle
the link variations caused by an inclined orbit geosynchronous satellite. Generally, the
buffer size may be set to 4 ms to take care of the periodic, 24-hour, link variations of the
satellite. Refer to paragraph 4.4.3.3.5 for a more complete discussion on the buffer
function within the modem.
4.4.3.2.1
Option Interface G.703, Overhead (AS/10175)
This interface is provided as a plug-in option card for the SLM7650 with user accessible
connectors at the rear of the modem as follows:
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The interface provides the following features:
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Additionally the option card is designed to support two build options as follows:
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Two BNC type female connectors for G.703 un-balanced interface
One 15-pin D-sub female connector for balanced G.703 interface
One 50-pin D-sub female connector for legacy equipment interfacing
G.703 data interface (balanced/un-balanced)
EIA422/MIL188 interface (50 pin connector)
ASYNC overhead data interface (50 pin connector)
Access to IDR/IBS Engineering Service Channels (ESC)
Drop & Insert
Build Option 1 (AS/10175-1) – G.703 data interface, EIA422/MIL188 interface,
ASYNC overhead data interface
Build Option 2 (AS/10175-2) – Includes all features of build option 1 with the
addition of Drop & Insert overhead and access to IDR/IBS ESC
4–18
Revision 4
MN/SLM7650.IOM
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