Glenayre Document Number: 9110.01002
GL-T8541 PA
09/10/99
THEORY OF OPERATION
t8541
p6.
fdk
Copyright © 1997 Glenayre
Page: 6-9
6.7 Metering Board
The metering board is mounted on the outside of the rear panel of the PA module. Refer to
Figure 6-6 for the block diagram of the metering board.
The metering board receives the +28 volt supply input and provides a +28 volt supply to
the driver board and each PA board. Each +28 volt feed to the PA passes through a current
monitoring circuit on the metering board. The PA currents are displayed on the DSP exciter
VDT display.
The metering board has four on board regulators used to produce the voltages needed to
operate the metering board. They are:
• the +34 volt supply
• the +7.5 volt supply
• the +5 volt supply
• the -15 volt supply.
The metering board receives the following three monitoring signals from the PA module,
they are:
• the heat sink temperature signal
• the forward power sample voltage
• the reflected power sample voltage.
The metering board receives the PA key input and the forward power reference signal from
the DSP exciter. It creates the pre-amp key signal from the PA key input, and the AGC
voltage from the forward power reference signal and the forward RF output power sample.
6.7.1 Temperature Monitoring Circuit
A portion of metering board is shown in Figure 6-4 to reveal the temperature monitoring
circuit. The heatsink temperature is monitored by a voltage divider consisting of fixed
resistor R143 on the metering board and temperature sensing resistor R5 on the combiner
board. R5 is thermally linked to the PA heat sink, and develops a voltage proportional to
the heat sink temperature. The voltage developed by R5 is passed through voltage follower
U5-A to the metering board multiplexing circuit.
