User Manual

RF-Orchestra!™ Transmitter Installation and Operation Operation
July 2000 6880493G02-C 5-33
Semiautomatic Carrier Feedthrough Nulling
This method requires a single FIPS command to initiate and execute the CFT nulling (RFO
FIPS: a 74). This method is normally performed during alignment and at a specified interval
thereafter. Normal paging traffic is halted for up to 30 seconds, while the Semi-automatic
Carrier Feedthrough Nulling is performed.
When the nulling is completed successfully, the new I and Q offset values are written to the
parameter database (parameters 979 and 980). Also, the 979A, 980A, 979B, 980B, Current
Ambient Temperature, and the Vif values (See Figure 5-18) are written to the EEPROM on the
Exciter. The 979A and 980A values will be used in subsequent semi-automatic and automatic
CFT nulling attempts to speed up the execution. If the Exciter EEPROM does not contain valid
CFT nulling parameters at startup, the 979A and 980A values will need to be acquired.
Figure 5-18: Ambient Temperature and Vif Values
Automatic Carrier Feedthrough Nulling
This method requires no user intervention. Auto CFT nulling is performed when there are
intervals or gaps in paging traffic which allow the RFO to make fine adjustments to the I and
Q offsets, to attain the minimum IF Voltage. Auto CFT nulling should be enabled in stations
transmitting InFLEXion voice traffic.
In order for Auto CFT Nulling to be effective, the station must have had an initial “complete”
nulling performed, at some time. If a “complete” nulling was performed, the CFT nulling
table will be present and valid in the Exciter EEPROM. If the Host does not detect a valid CFT
nulling table, and Auto CFT Nulling is Enabled (RFO FIPS: w 998 1), the RFO will
automatically perform a “complete” nulling, and store the results in the Exciter EEPROM, at
the first opportunity. Once the “complete” null has been completed successfully, and the table
Txlin Register $12
Init 0x0c 0x04 0x08 Final
----------------------------------------
979 -385
980 -682
Vif ----- 0.16 0.16 0.16 -----
=============================================
I Offset
Q Offset
IF Voltage
(979A) (979B) (979A) (979B)
(980A) (980A) (980B) (980B)
I and Q
Slew
Rate
Limiters
Disabled
Initial
Values
(prior to
CFT nulling)
Q
Slew
Rate
Limiter
Disabled
I
Slew
Rate
Limiter
Disabled
Final
Values