Mocomtech CIM-550 - Manual (Page 68)

CiM-550 IP Enabled Satellite Modem Rev. 2
Front Panel Menus CD/CIM550.IOM
42
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.
The three loopback modes are illustrated in the following figure.