Comtech EF Data CDM-625A - Manual (Page 138)

CDM-625A Advanced Satellite Modem MN-CDM625A
Front Panel Operation Revision 3
6–12
6.2.1.3 CONFIG: Tx
Tx-IF Freq Power FEC Mod Data Scrambler
(Data 00192.000kbps, 00131.657ksps) ()
On the top line – Use the ◄ ►arrow keys to select a parameter. Press ENTER.
On the bottom line – Read-only Data and Symbol rate information is provided.
When Sub-Mux is ON, Composite Rate information replaces the Data Rate
information on the bottom line of this display.
6.2.1.3.1 CONFIG: Tx  Tx-IF
Tx: Carrier=On (Off,On,RTI) POCO=Off
SpectrumInvert=Off Txα=.35(.05-.35)()
Use the ◄ ►arrow keys to select a parameter. Press ENTER.
• Carrier – Use the ▲▼ arrow keys to select a parameter. Press ENTER.
USE THE RTI FEATURE WITH EXTREME CARE! RTI (RECEIVE/TRANSMIT INHIBIT),
when selected, prevents transmission of the Tx carrier until the demodulator is
locked. To avoid shutdown of the Tx Carrier when the demodulator loses lock for
a very short duration, before the transmit carrier is inhibited the demodulator
must be unlocked continuously for the selected time period (1, 2, 4, 7, or 10
seconds).
Enabling RTI does not affect the Internal IF Loopback feature. However, be aware
that, if an External IF Loopback is attempted (i.e., connecting an external cable
from the Tx IF output to the Rx IF input), this will not work! (The Tx carrier cannot
turn on until the demod is locked – the demod cannot lock because the Tx output
is off. The net result is that the demod will not lock and the Tx carrier will not turn
on.)
• POCO (Power-On Carrier-Off) – When enabled (selected as ON), this feature overrides the
Tx setting to OFF in the event of a power-cycle of the modem. Use with caution.
SPECTRUM INVERT should normally be in the OFF position. For all FEC types
except BPSK, when Spectrum Invert is in the ON position the transmit spectrum
is inverted (which is the same as reversing the direction of phase rotation in the
modulator). In BPSK, the time-order of bits out of the FEC encoder is reversed to
make the modem compatible with certain other manufacturer modems.