Glenayre Document Number: 9110.00160
250-Watt Gold Line Power Amplifier
Issue 1, Rev. C: 10/21/96
THEORY OF OPERATION
Print Date: 12/17/96
Copyright © 1996 Glenayre
Page: 6-3
6.2
RF Distribution
Refer to
Figure 6-1
. The PA RF input is received through a BNC connector, which mates
with J3 on the exciter/PA control. This RF input signal (at a nominal 350 mW) is split and
amplified into two RF signals (at a nominal 40 watts) by the driver board. Each RF signal
is amplified (to a nominal 150 watts) by a PA board. These RF signals are combined into
one RF signal (at a nominal 275 watts) by the combiner board. This is the PA RF output,
and is applied to an isolator. The isolator RF output (at a nominal 250 watts for standard)
is supplied to an antenna for transmission. All power levels given here and in the following
paragraphs are typical; actual power levels will vary from those given.
6.2.1
Driver Board RF Flow
The driver board splits and amplifies a 350-mW RF input into two 40-watt RF outputs.
Refer to
Figure 6-3
. The RF input to the driver board is applied to the preamplifier module
(Q1). A portion of the RF input is applied to an RF-detection circuit on the board. This
circuit rectifies and filters the RF input into an OK signal. Loss of the RF input and the OK
signal results in an exciter output fault.
The preamplifier module is a three-stage RF power amplifier on a single IC. The first and
third stages are powered by an AGC signal. These are the variable gain stages, and control
the forward power output of the PA. The first and third stages of the preamp module are
powered by an AGC signal, generated on the metering board. AGC signal voltage is
monitored for status only. The second stage of the preamplifier module is a nonvariable-
gain stage, powered by +13.5-volt power. The current drawn by the AGC and +13.5-volt
power signals contributes to the preamplifier current metering.
The amplified RF output from the preamp module is applied to the IPA (Q2). The current
drawn from the IPA’s +25-volt power source is monitored to determine the IPA current
metering. The amplified RF output from the IPA is monitored for forward and reflected
power levels. The power samples detected at this location determine the IPA forward - and
reflected-power metering.
Power-Monitoring Theory
Power-monitor circuits are located on the driver board, PA boards, and combiner
board. A microstrip line parallel to the RF signal path couples a small portion of the ac
signal across a rectifier and filtering circuit. The ac signal may be rectified to detect ei-
ther the forward or reflected power. After filtering, a dc sample voltage is available that
is proportional to the power detected at the monitored location.
