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116 Power Amplifier Circuit Description TB8100 Service Manual

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.

7.1.2 PA-Key

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.

7.1.3 Power Foldback

The PA control circuitry will reduce the RF output power to P

min

when

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.

min

is defined as follows:

1. The accuracy of the measurement of the parameter values is subject to the

tolerances listed in the Specifications Manual.

Model P

min

5W 1W

50W 5W

100W 10W

Tait TB8100 Service Manual

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