120 Power Amplifier Circuit Description TB8100 Service Manual
© Tait Electronics Limited September 2006
7.1.9 Ambient Air Temperature Sensor
The PA ambient air temperature sensor board may be fitted in one of two
positions. It is inserted through the appropriate slot in the control board and
plugs into a 3-way connector. The sensor board is positioned between the
heatsink fins and requires forced airflow to perform an accurate
measurement.
Note You must fit the sensor board in the correct location to ensure that
the temperature of the airflow over the sensor is nearest the ambi-
ent temperature of the air from the cooling fan. Figure 8.1 on
page 130 and Figure 8.2 on page 131 show the correct location of
the sensor board in each model of PA.
7.2 RF Circuitry
Refer to Figure 7.2 on page 117.
7.2.1 6W Board
The 11dBm (±2dB) RF input is fed to the variable PIN diode attenuator
which provides power control. From the PIN diode attenuator the signal is
fed via a 100mW gain block and a 1W gain stage to a 6W transistor where
it is amplified to the final output level of 6W. This 6W transistor forms the
output stage of the 5W PA and is the driver stage for the 50W and 100W
PAs.
The gain block and 1W transistor operate off a +10V switched supply,
while the 6W driver transistor operates off a +28V supply.
The 6W board also has circuitry to monitor the drain current and
temperature of the 6W transistor, and the presence of an RF input signal.
7.2.2 60W Board
The output from the 6W board is fed to the 60W final transistor which
amplifies the signal to an output power of 60W. The 60W transistor
operates off a +28V supply.
The 60W board also has circuitry to monitor the drain current and
temperature of the 60W transistor.
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