Comtech EF Data CDM-710 Installation And Operation Manual page 108

CDM-710 Broadcast Satellite Modem
Front Panel Operation
Each test mode option is further explained as follows:
SELECTION
Norm
IF
I/O
RF
Tx-CW
Tx-1,0
Block Diagrams for the I/O,IF, and RF Loopback Test modes are illustrated in Figure 5-3.
DESCRIPTION
(Normal) This clears any test modes or loopbacks and places the unit back into an operational state.
(IF Loop) This test mode invokes an internal IF loop. 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.
(Input / Output Loop) This test mode invokes two distinct loopbacks. The first Loopback is an inward loop
that 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 Loop) This RF loop 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.
(Transmit CW) This test mode forces the modulator to transmit a pure carrier (unmodulated).
(Tx 1, 0, 1, 0 Pattern) This is a test mode that 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 quadrature and amplitude balance.
5–44
Revision 11
MN/CDM710.IOM