Comtech EF Data CDM-500 - Manual (Page 45)

Front Panel Operation CDM-500 Closed Network Satellite Modem
6–16 Rev. 1.3
6.6 TEST
TEST: NORM TX-CW TX-1,0
IF] DIG] I/O] (ENT)
Select NORM, TX-CW, TX-1,0, IF LOOP, DIG LOOP, or I/O LOOP, using the
LEFT/RIGHT arrow keys, then press Enter.
This sub-menu permits the user to select the following test modes:
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.