Comtech EF Data DMD1050 - Manual (Page 40)

DMD1050 Satellite Modem Board Theory of Operation
MN-DMD1050 3–14
Revision 9
3.9 Loopback Features (Terrestrial & IF)
The modem provides for a number of different loopbacks. The Loopback supported are:
 IF Loopback – Tx IF port is looped back to the Rx IF port
 TX Terrestrial Loopback - Tx Data port is looped back to the Rx Data port after the
interface driver/receiver. (prior to the framing unit)
 TX Baseband Loopback - Tx Data port is looped back to the Rx Data port after the
interface driver/receiver. (after the framing unit)
 RX Terrestrial Loopback - Receive Data from the satellite is looped back for retransmission
to the satellite, providing a far end loopback. (prior to the framing
unit)
 RX Baseband Loopback - Receive Data from the satellite is looped back for retransmission
to the satellite, providing a far end loopback. (after to framing unit)
 TX/RX Terrestrial Loopback - provides both Terrestrial loopbacks simultaneously
 TX/RX Baseband Loopback - provides both Baseband loopbacks simultaneously
Refer to Figure 3-6 through Figure 3-8 for loopback functional block diagrams.
Usage of the modems loopback capabilities in conjunction with the
Ethernet data interface can produce undesirable network loops. In order
to run any type of data test with an Ethernet interface you must utilize
two modems connected back to back. Simply using one modem and a
loopback will not produce the desired results.
IMPORTANT