Baseband Interface; Monitor And Control; Transmit And Receive Baseband - Comtech EF Data SLM-7650 Installation And Operation Manual

SLM-7650 Satellite Modem
Theory of Operation
The Sweep Range sets limits of the carrier loop during acquisition. The Sweep Center
Frequency function allows the operator to target the demod center frequency to be offset
from the assigned demodulator center frequency. The Reacquisition function is used to
reduce the amount of time that is required to relock the demod in the event of a short
outage or fade. For the time specified in the Reacquisition function, the demodulator will
reduce the sweep range of the carrier loop to +/-500 Hz from the demodulator center
frequency prior to the outage.
4.4.3

Baseband Interface

The baseband section of the modem consists of the Monitor and Control (M&C), the
transmit and receive baseband interface section, and the reference and clock distribution
section.
4.4.3.1

Monitor and Control

The remote serial monitor and control port is selectable as RS-232 or RS-485. The
remote control port is used to retrieve status or provide user control of the modem from a
remote location and is also used to upgrade the firmware on each CCA.
A fault connector provides Form C contacts for reporting faults on each CCA.
4.4.3.2

Transmit and Receive Baseband

The primary data channel is available on a TIA/EIA-449, 37 pin or an optional TIA/EIA-
530, 25 pin subminiature D-shell connector. The data and clock signals conform to MIL-
188-114 type II and III, and TIA/EIA-422 balanced data and clock signal levels.
The digital data baseband loopback occurs between the transmit and receive sections of
the modem. This baseband loopback is a bi-directional loop at the input and output of the
interface drivers and receivers. This will allow the operator to verify a valid baseband
connection to the modem.
An overhead channel is available for Asynchronous (ASYNC) serial communications
between the two ends of the satellite link and Automatic Uplink Power Control (AUPC).
This overhead channel increases the symbol rate by 6.7%. This overhead function is a
closed network application that is compatible with an SLM-8650 operating in 8650-02
mode. The interface for the overhead data is available on a 9 Pin 'D' connector at the rear
panel of the modem. The electrical interface is selectable TIA/EIA-232 or TIA/EIA-485
(2 or 4 wire).
Intelsat specifies an overhead framing structure for every open network carrier. The
specifications from Intelsat are IESS-308, IESS-309, and IESS-310. The modem can be
configured to provide IDR and IBS framing of the data stream per the Intelsat
specifications. The type of overhead framing over Intelsat is dependent on the data rate,
modulation type, and service that are in operation. Refer to the IESS documents for
complete details on these operating modes and framing format.
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MN/SLM7650.IOM