User Manual

Operation RF-Orchestra!™ Transmitter Installation and Operation
5-34 6880493G02-C July 2000
values have been stored in the Exciter EEPROM, subsequent resets of the station will not
require additional “complete” CFT nullings. If the “complete” nulling is unsuccessful (due to
bad exciter, or transmitter becomes disabled, etc.), a “CFT Nulling Failed” error will be
logged. The RFO will repeat nulling attempts at all subsequent opportunities, and will
continue to log “CFT Nulling Failed” errors as they occur. In order to notify the control center
of a potential problem with the transmitter, a “CFT Nulling Failed” alarm is also be logged.
CFT nulling will take on two possible automatic forms: Auto CFT Nulling, and DC Offset
Training. The DC Offset Training is explained below. Auto CFT Nulling is a time-critical
operation that is to be performed by the RF-O! software at the appropriate opportunity. A
single RF-O! EEPROM parameter (998) is used to control the type of nulling to be performed.
If parameter 998 is set 0, neither Auto CFT Nulling nor DC Offset Training will be performed.
If it is set to 1, Auto CFT Nulling will be enabled. If it is set to 2, DC Offset training will be
enabled.
When enabled, Auto CFT Nulling makes fine adjustments to the current I and Q offset values
during all "Synch-Only" InFLEXion frames. The entire adjustment takes less than 1.3 seconds
to execute.
Figure 5-19: Timing Diagram for Automatic CFT Nulling
DC Offset Training
DC Offset Training should be used in transmitters which will only be used for FLEX or
ReFLEX (no InFLEXion) applications.
Keyed
Workahead
Time
~100 ms
FM Sync-Only Frame
Perform CFT Nulling (Less than 1.6 seconds)
Ctl Cmd A
90 ms
Ctl Cmd B
B
A
Dekeyed