Maintenance M7/M7L/M7LT Modular Satellite Modem
4-4 M7/M7L/M7LT - Rev. 0.05
4.3.1.1. Near End Terrestrial Data Loopback:
The near end terrestrial data loopback will be the closest loopback to the input data connection of the
modem. If data is returned and received properly this loopback will indicate the DTE wiring and
connection to the modem are correct. This loopback is set in <Intf: Test - Ter Loopback>.
NOTE: This test requires an external source of data.
4.3.1.2. Near End Satellite Data Loop-Back
The near end satellite data loopback test is used to return the data that was received over a proper
satellite link back over the satellite to be received at the other end of the link. This loopback tests the
complete satellite link and the modems at both ends of the link. This loopback is set in <Intf: Test -
Sat Loopback>.
NOTE: This is a uni-directional loopback and no data will be returned to the terrestrial side of the
modem.
4.3.1.3. Near End IF Loop-Back:
This loop-back test will verify the modem transmit data signal processing, modulation, demodulation,
receive signal processing, and connection to the receive interface. This loopback is set in IF loop-
back in <Dem: Test - IF Loopback>.
4.3.1.4. Far End Satellite Data Loop-Back:
This loopback will test most of the satellite link as well as the functions checked in paragraph 4.3.1.3
above. The signal is sent over the satellite (or test setup) and is looped back at the satellite side of
the data interface on the far end modem. This tests both modems, the satellite link and originating
end wiring. The M7 sets the satellite side loop-back in <Intf: Test - Sat Loopback>.
NOTE: In this test, the near end satellite and IF loop-back functions should not be enabled whether
using the internal or an external BERT. Setting this mode slaves the modulator timing to the
demod timing and the FIFO buffer remains engaged if enabled.
In this type of testing an external BERT is typically set to provide a terminal timing output, while the
connected modem is set to use the terminal timing signal as the transmit bit rate clock source. This
modem can alternatively be set to use its internal clock for the transmit clock timing and provide that
signal to the BERT for synchronization. More information on using the M7’s internal BERT is given
below.
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