Mocomtech CDM-570 - Manual (Page 174)

CDM-570/570L Satellite Modem with Optional IP Module Revision 4
Front Panel Operation MN/CDM570L.IOM
6–50
6.15 TEST
Select Norm, IF Loop, Dig Loop, I/O Loop, RF Loop, Tx-CW, or Tx-1,0, using the
◄ ► 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.
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. During an IF Loop, the Tx carrier continues to be
transmitted. See Figure 6-4
Dig Loop
(Digital Loopback) This test mode invokes a digital loopback, which loops
data at the output of the framer/scrambler on the transmit side, back into the
deframer/descrambler on the receive side. If concatenated Reed-Solomon
FEC is being used, this is also included in the digital loop. See Figure 6-4
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. See Figure 6-4
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 satellite loopback. When NORMAL is again selected, all of
the previous values are restored.
TX-CW
(Transmit CW) This is a test mode which forces the modulator to transmit a
pure carrier (unmodulated). Used for measuring phase noise.
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
OQPSK is selected as the modulation type, the test will produce a spectral
pattern suitable for the measurement of SSB rejection – useful in
determining the phase and amplitude accuracy of the modulator.
TEST: Norm IF> Dig> I/O>
RF> Tx-CW Tx-1,0(
◄ ►,ENT)