Comtech EF Data CDM-600/600L - Manual (Page 107)

CDM-600/600L Open Network Satellite Modem Revision 3
Front Panel Operation MN/CDM600L.IOM
5–31
5.5 SELECT: TEST
MODEM TEST MODE = NORMAL
(NORM,TX-CW,TX-1/0,IF
↓,RF↓,DIG↓,I/O↓)
Select NORM (Normal Operation) or a Test Mode from the parameters shown in the parentheses
on the bottom line.
Use the[ ↑][↓] arrow keys, then press [ENT], to select one of the following modes:
Selection Description
NORM
(Normal) This clears any test modes or loopbacks, and places the unit back into
an operational state.
TX-CW
(Transmit CW) This is a test mode, which forces the modulator to transmit a
pure carrier (unmodulated).
TX-1/0
(Transmit an alternating 1,0,1,0 pattern) This test mode forces the modulator
to transmit a carrier modulated with an alternating 1,0,1,0 pattern, at the currently
selected symbol rate. This causes two discrete 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.
IF
↓
(IF Loopback) 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 receive configuration
parameters are temporarily changed to match those of the transmit side. When
Normal is again selected, all of the previous values are restored.
RF
↓
(RF Loopback) This test mode is almost identical to the IF loop mode. 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. This is useful for performing a satellite loopback. When Normal is again
selected, all of the previous values are restored.
Dig
↓
(Digital Loopback) This test mode invokes a digital loopback, which loops data
at the output of the Reed-Solomon encoder on the transmit side, back into the
Reed-Solomon decoder on the receive side. This tests all of the interface,
transmit baseband circuits, FEC encoder, FEC decoder, and buffer.
I/O
↓
(Inward/Outward Loopback) This test mode invokes two distinct loopbacks.
The first of these 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.
The IF, Digital, and I/O Loopback Test modes are illustrated in Figure 5-3.