Pa-Key; Power Foldback - Tait TB8100 Service Manual

7.1.2

PA-Key

7.1.3

Power Foldback

116 Power Amplifier Circuit Description
A red LED visible from the front panel of the PA will light to indicate a
summary alarm.
For a more detailed description of alarms and diagnostics refer to the Service
Kit User's Manual or on-line help.
The PA is keyed by a +8VDC signal which is superimposed on the RF
signal on the coaxial input cable.
The key-up sequence requires the RF input (+11dBm) to be turned on and
stable before the PA is keyed on. When the PA is keyed off, the RF input
is turned off only when the key-down sequence is complete.
The PA control circuitry will reduce the RF output power to P
any one of the following fault conditions occurs:
the temperature of the 6W board, 60W board 1 or 60W board 2
exceeds the maximum allowable temperature
the supply voltage drops to between 24 and 26VDC or rises to between
30 and 32VDC
the load VSWR is ≥10:1 (foldback is deactivated when the VSWR is less
than 5:1)
the transmit current of the 6W driver transistor, 60W final transistor 1
or 60W final transistor 2 exceeds the maximum allowable current.
P is defined as follows:
min
Model
5W
50W
100W
1. The accuracy of the measurement of the parameter values is subject to the
tolerances listed in the Specifications Manual.
1
P
min
1W
5W
10W
© Tait Electronics Limited September 2006
when
min
TB8100 Service Manual