Comtech EF Data CDM-760 - Manual (Page 144)

Front Panel Operation Revision 2
CDM-760 Advanced High-Speed Trunking Modem MN-CDM760
6–58
6.2.4 SELECT: Test
TEST: Mode BERT Comp
()
Use the   arrow keys to select a parameter. Press ENTER.
6.2.4.1 (TEST:) Mode
Modem Test Mode:Normal
()
Use the arrow keys to select an available Test Mode. Press ENTER to execute.
Available selections are:
Selection Description
Normal This clears any test modes or loopbacks, and places the unit back into an operational state.
Tx-CW (Transmit CW) This mode forces the modulator to transmit a pure carrier (unmodulated).
Single Side Band
This mode should not be enabled over the satellite.
This mode demonstrates the modulator’s carrier null, amplitude, and phase balance. A
single carrier on one side of the nominal center Tx frequency, offset from the nominal carrier
frequency by half of the configured symbol rate.
IQ PN Sequence
This mode transmits random unframed data to the Nyquist filters. Use this to measure
spectral mask as there is no correlation due to framing or terrestrial data patterns.
RF-Loop
(RF Loopback) Use this mode to perform a satellite loopback. It is almost identical to the IF
loop mode, except that all of the receive configuration parameters (except Rx Spectrum
Invert) are temporarily changed to match those of the transmit side. However, no internal
connection is made. When Normal is again selected, all previous values are restored. See
Figure 6-3 for the flow diagram for this test.
IF-Loop
(IF Loopback) This mode invokes an internal IF loop. It is a particularly useful test in that it
permits you to perform a quick diagnostic test without having to disturb external cabling.
Furthermore, all receive configuration parameters are temporarily changed to match those
of the transmit side. When Normal is again selected, all previous values are restored. See
Figure 6-3 for the flow diagram for this test.
Dig-Loop
Digital Loopback) This mode tests the entire interface, transmit baseband circuits, and
buffer. It invokes a Digital loopback, which loops data at the output of the framer on the
transmit side back into the framer on the receive side. See Figure 6-3 for the flow diagram
for this test.
I/O-Loop
(I/O Loopback) This mode invokes two distinct loopbacks: The first is the inward loop,
which takes data being received from the satellite direction and passes it 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.