Test - Comtech EF Data CDM-550T Manual

Front Panel Operation
6.2.4

TEST

TEST: NORM
IF] DIG] I/O] RF]
Select NORM, TX-CW, TX-1,0, IF LOOP, DIG LOOP, I/O LOOP or RF LOOP, using
the LEFT/RIGHT arrow keys, then press ENTER.
This sub-menu permits the user to select the following test modes:
NORM
TX-CW
TX-1,0
IF LOOP
DIG LOOP
I/O LOOP
RF LOOP
The IF LOOP, DIG LOOP and I/O LOOP modes are illustrated in Figure 6-2.
6–28
TX-CW TX-1,0
(ENT)
(Normal) This clears any test modes or loopbacks, and places the unit back into an
operational state.
(Transmit CW) This is a test mode which forces the modulator to transmit a pure carrier
(unmodulated).
(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 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.
(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.
(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 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.
CDM-550T Satellite Modem
Rev. 1.3