M7/M7L/M7LT Modular Satellite Modem OperationM7/M7L/M7LT - Rev. 0.05 1-19Figure 1-17 - Dual Interface Configuration I7 and G7Figure 1-18 - Dual Interface Configuration E7 and G71.5.4. Bit Rate Timing OptionsThe Modulator and the Demodulator each have four (4) possible sources for their bit rate timing.These clock sources may be used in various ways in a system implementation to provide correcttiming at a destination. Each of the clock sources can be set either from the front panel or from anexternal monitor and control system. Refer to Section 3.9 for details about these options and how toconfigure the modem for each of these timing options.1.5.5. Data Interface Loop-Back FunctionThe standard and most optional interfaces also provide the data loop-back function. The data loop-back can be controlled from the front panel or via remote control command. The data towards boththe terrestrial and satellite sides can be looped back individually by enabling this function via the frontpanel or remote controlThe data loop-back allows testing of the signal path connection up to the loop-back and back to thesource. Since both terrestrial and satellite sides of the signal path can be looped, the connection froma local DTE can be checked on the terrestrial side while the connection from the far end DTE over thesatellite and through the modem can be checked on the satellite side. More information on use of theloop-back modes is given in Section 4.3.NOTE: Ethernet interfaces do not have this function. CAUTION: Enabling the “Data Loop-Back” functions will result in loss of traffic. It should not beused in operating links without prior arrangements.
