Comtech EF Data OM20 - Manual (Page 47)

OM20 Universal Outdoor Modem OM20 Theory of Operation
MN-OM20– Revision 5 4–9
 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
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.