Comtech EF Data CDM-700 - Manual (Page 112)

CDM-700 High Speed Satellite Modem Revision 5
Front Panel Operation MN/CDM700.IOM
6–58
6.3.3 (SELECT:) Test
Test: Norm IF↵ Dig↵ I/O↵
RF↵ Tx-CW Tx-1,0 ( E)
Select Norm, IF Loop, Dig Loop, I/O Loop, RF Loop, Tx-CW, or Tx-1.0 using the ◄ ►
arrow keys. Press
ENTER
.
The CDM-700 supports many useful test modes. Not all modes are available in all configurations – they
depend upon the modem configuration (Duplex, Rx-Only, Tx-Only) and the data interface(s):
Norm
This clears any test modes or loopbacks and places the unit back into an
operational state.
IF
↵
This test mode invokes an internal IF loop (Figure 6-3). This is a
particularly useful feature, as it permits the user to perform a quick
diagnostic test without having to disturb external cabling. Furthermore, all
of the Rx configuration parameters are temporarily changed to match
those of the Tx-side. When Norm is again selected, all of the previous
values are restored.
Dig
↵
This test mode invokes a digital loopback (Figure 6-3), which loops data at
the output of the encoder on the Tx-side, back into the Reed-Solomon
decoder on the Rx-side. This tests all of the interface, Tx baseband
circuits, FEC encoder, FEC decoder, and buffer.
I/O
↵
This test mode invokes two distinct loopbacks (Figure 6-3). The first
Loopback is an 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 Tx data
interface is routed directly back out of the Rx data interface.
RF
↵
This RF loop (Figure 6-3) is almost identical to the IF loop mode. All of the
Rx configuration parameters (except Rx Spectrum Invert) are temporarily
changed to match those of the Tx-side, however, no internal connection is
made. This is useful for performing a satellite Loopback. When Norm is
again selected, all of the previous values are restored.
Tx-CW
This is a test mode, which forces the modulator to transmit a pure carrier
(unmodulated).
Tx-1,0
This is a test mode, which forces the modulator to transmit a carrier
modulated with an alternating 1,0,1,0 pattern, at the currently selected
symbol rate. This causes single sideband spectral lines to appear, spaced
at
± half the symbol rate, about the carrier frequency. This mode is used to
check the carrier suppression of the Modulator. Also, it verifies gradrature
and amplitude balance.
Note: Available loopbacks depend upon modem configuration and the data interface(s)
installed.