Comtech EF Data CDM-550T Manual page 39

CDM-550T Satellite Modem
(CONFIG, TX) ON/OFF
Rev. 1.3
TX TURBO:3/4(Q) 21/44(B)
5/16(B) 3/4(OQ) (ENTER)
(CONFIG, TX, FEC, RATE) FEC Rate (Turbo Only)
Select Rate 3/4 (QPSK), Rate 21/44 (BPSK ONLY) Rate 5/16 (BPSK ONLY) or
Rate 3/4 (OQPSK) encoding rate, using the LEFT/RIGHT arrow keys, then press
ENTER. Note that the Rate 3/4 OQPSK is new for Version 1.19.
(For further details, see Section 7 - 'FEC Options'.)
SELECT TX OUTPUT STATE:
ON OFF RTI
Select either ON, OFF, or RTI, using the LEFT/RIGHT arrow keys, then press
ENTER.
* NEW FEATURE * 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.
IMPORTANT NOTE: Having this feature enabled does not affect the internal IF
loopback feature. But, please be aware 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 ouput is off. The net result is
that the demod will not lock, and the Tx carrier will not turn on. PLEASE USE
THE RTI FEATURE WITH EXTREME CARE!
(ENTER)
Front Panel Operation
6–9