Comtech EF Data CDM-550T - Manual (Page 48)

CDM-550T Satellite Modem Revision 3
Front Panel Operation MN/CDM550T.IOM
6.2.3.1.6 (CONFIG: TX) SCRAM (Scrambling)
Select either ON or OFF, using the [
←] [→] arrow keys, then press ENTER.
When Transparent mode is selected, a V.35 scrambler is used. In Framed or Reed-Solomon
modes, a frame synchronised scrambler is used.
SELECT TX SCRAMBLING:
OFF ON (PRESS ENTER)
6.2.3.1.7 (CONFIG: TX) CLK (Clocking)
Select INT (Internal), EXT (External) or LOOP-TIMED, using the LEFT/RIGHT arrow keys,
then press ENTER.
SELECT TX CLOCKING MODE:
INT EXT LOOP-TIMED (ENT)
INTERNAL
indicates that the CDM-550T will supply a clock to the DTE, which is derived
from its internal high-stability source.
EXTERNAL
indicates that the CDM-550T expects to receive a clock from the DTE, to
which the unit can phase-lock its internal circuits.
LOOP-TIMED
indicates that the transmit timing source should be the receive clock, from
the direction of the satellite. This is a useful mode, in that no external
connection needs to be made in this mode. If the demodulator loses lock, or
if there is no receive signal present, the internal clock is substituted. Note
also that this mode will work even with asymmetric RX and TX data rates.
6.2.3.1.8 (CONFIG: TX) TSI (Transmit Spectral Invert)
Select either OFF or ON, using the [
←] [→] arrow keys, then press ENTER.
When in the ON position, and QPSK is selected, 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’s modems.
SELECT TRANSMIT SPECTRAL
INVERSION: OFF ON(ENTER)
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