Comtech EF Data SDM-100A User Manual
Page 136
Theory of Operation
SDM-100A Satellite Modem
4–20
Rev.
0
The Request to Send (RTS) line is hard-wired to the Clear to Send (CTS) line by JP11,
pins 5 and 6, on the Demodulator/M&C card (AS/4973), since the modem does not
support polled operation.
Data Set Ready (DSR) indicates that the modem is powered up.
Receive Line Signal Detect (RLSD) indicates that an RF carrier is being received and
demodulated with a sufficiently low error rate for the decoder to remain locked.
The V.35 interface also provides bi-directional relay loopback of both the clock and data
at the DCE interface. In LOOPBACK:
• From the DTE side, SD is connected to RD, and either SCT or SCTE (in
INTERNAL or EXTERNAL mode) is looped back to SCR.
• From the modem side, the received data and recovered clock are routed back to
the modulator input for retransmission.
Loop timing is supported by the selection of the RX Satellite Clock source in the
Interface Configuration menu of the front panel for “TX Clock Source.” When RX
Satellite is selected, the transmit clock (ST) is replaced by the clock recovered from the
satellite (RT).
Three fault outputs are provided on dry contact Form-C relays:
• COMMON
EQUIPMENT
• MODULATOR
• DEMODULATOR
They are available on the FAULT connector on the modem rear panel.
Generation of these fault conditions is described in Chapter 3.
Fault indicators are also provided on TTL open collector drivers on the V.35 connector:
• The TTL MOD fault indicates one of the following:
MODULATOR
fault
COMMON EQUIPMENT fault
• The TTL DEMOD fault indicates one of the following:
DEMOD
fault
COMMON EQUIPMENT fault