4-32 888-2406-002
WARNING: Disconnect primary power prior to servicing.
Overall System Theory
All the individual bits or bytes of information stored here have a default setting
which is stored in the firmware ROM. When the information in U39 is uploaded to
RAM it is checked against the default values. If it is considered to be out of
tolerance (or invalid data) it will automatically be replaced with the default value
from the ROM. When this happens the fault “EEPROM_DEF” (Default) will be
placed in the fault log. The only time this should happen is when a new EEPROM,
U39 is installed in the Master Controller. Since it is basically blank, all of the
default settings from the ROM will be written to U39 one at a time as it finds they
are out of tolerance. After this has happened, the EEPROM_DEF fault should never
happen again. If it does, U39 should be replaced since a memory location is
probably bad. For information on replacing EEPROM U39 see Section V,
Maintenance and Alignments.
The following is a listing of all of the Default Values which are stored in the
Firmware:
• Forward Factor - 0.003079
• Reflect Factor - 0.000123
• Cal APC Factor - 3.03
• Cal Frequency - 98MHz
• Operating Frequency - 98MHz
• IPA Factor - 200
• Exciter Factor - 200
• TPO 100% - 02.00kW
• Max High - 03.00kW
• Max Low - 01.00kW
• UPS Setting - 01.00kW
• Low Power Alarm - 01.80kW
• VSWR Foldback - 1.35
• VSWR Fault - 1.5
4.7.1.2 APC, Automatic Power Control
One important function of the Master Controller is transmitter power control, which
is accomplished via the APC Loop. The APC Loop controls the transmitter power
and keeps it constant by varying the IPA RF output indirectly proportionate with the
forward power. In other words, if the forward power output goes up, the IPA output
will be reduced, which will in turn reduce the PA RF output. If the forward power
output goes down, the IPA RF output will be increased, which will increase the PA
RF output to compensate.
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