Comtech EF Data CDM-425 Installation And Operation Manual page 193

CDM-425 Advanced Satellite Modem
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Setting Function
(RF Loopback) Use this test mode to perform a satellite loopback. It is almost identical to the
IF loop mode, except that all receive configuration parameters (except Rx Spectrum Invert)
RF-LOOP (RF↓)
are temporarily changed to match those of the transmit side; however, no internal connection
is made. All previous values are restored once Normal is again selected.
(Digital Loopback) Use this test mode to invoke a digital loopback, which loops data at the
Dig-Loop
output of the Reed-Solomon encoder on the transmit side and back into the Reed-Solomon
decoder on the receive side. This tests the entire interface, transmit baseband circuits, FEC
(DIG↓)
encoder, FEC decoder, and buffer. See Figure 5-3.
(Inward/Outward Loopback) Use this test mode to invoke two distinct loopbacks. The first is
the inward loop, which takes data being received from the satellite direction and passes it
I/O-Loop (IF↓)
directly to the modulator. Simultaneously, the outward loop is invoked, whereby data being
fed to the transmit data interface is routed directly back out of the receive data interface. See
Figure 5-3.
Front Panel Operation 6–75 MN-CDM-425