CDM-625 Advanced Satellite Modem
Revision 1
Front Panel Operation
MN-0000036 (Ref MN/CDM625.IOM)
5.4.3
CONFIG: Tx
Tx-IF Freq Power FEC Mod Data Scrambler
(Data 00192.000kbps, 00131.657ksym) (
34
)
Select the parameter on the top line using the
◄
►
arrow keys – the submenu branches available
are
Tx-IF
,
Freq
,
Power
,
FEC
,
Mod
,
Data
, and
Scrambler –
then press
ENTER
. Observe the
Data/Symbol rate information on the lower line.
5.4.3.1
CONFIG: Tx
Æ
Tx-IF
Tx: Carrier=On (Off,On,RTI) POCO=Off
Spectrum Invert=Off (Off,On)
(
34v
)
Three Tx settings can be set from this menu. Select the parameter to edit using the
◄
►
arrow
keys. The available options are shown in parentheses. Edit the setting using the
▲
▼
arrow keys,
then press
ENTER
when done.
IMPORTANT
RTI means RECEIVE/TRANSMIT INHIBIT. When selected, it will prevent the
Tx carrier from being transmitted until the demodulator is locked.
To avoid
the Tx Carrier from being turned off when the demodulator loses lock for a
very short period of time, the demodulator must be unlocked continuously
for a period of 10 seconds before the transmit carrier is inhibited. This time
interval is fixed and the user cannot change it.
Having this feature enabled does not affect the internal IF loopback feature.
Be aware, however, that if an external IF loopback is attempted (connecting
an external cable from the Tx IF output to the Rx IF input), then this will not
work! (The Tx carrier cannot turn on until the demod is locked, and 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. USE THE RTI
FEATURE WITH EXTREME CARE!)
POCO is an acronym for Power-on Carrier-off. When enabled, this feature overrides the Tx
setting to OFF in the event of a power-cycle of the modem.
Use with caution
.
IMPORTANT
SPECTRUM INVERT should normally be in the OFF position. When in the
ON position, for all FEC types, except BPSK, 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.
5–10
