Comtech EF Data CDM-550T - Manual (Page 61)

CDM-550T Satellite Modem Revision 3
Front Panel Operation MN/CDM550T.IOM
6.2.4 SELECT: TEST
Select NORM, TX-CW, TX-1,0, IF LOOP, DIG LOOP, I/O LOOP or RF LOOP, using
the [
←] [→] arrow keys, then press ENTER.
This sub-menu permits the user to select the following test modes:
TEST: NORM TX-CW TX-1,0
IF] DIG] I/O] RF] (ENT)
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 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 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 LOOP
(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.
DIG LOOP
(Digital Loopback) This test mode invokes a digital loopback, which loops data
at the output of the digital FIR filter on the transmit side, back into the Viterbi
decoder on the receive side. This tests all of the interface, transmit baseband
circuits, FEC encoder, FEC decoder, and buffer.
I/O LOOP
(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.
RF LOOP
(RF Loopback) This test mode is almost identical to the IF loop mode. All of the
receive configuration parameters are temporarily changed to match those of
the transmit side, however, no internal connection is made. This is useful for
performing a satelite loopback. When NORMAL is again selected, all of the
previous values are restored.
The IF LOOP, DIG LOOP and I/O LOOP modes are illustrated in Figure 6-4.
6–25