User Manual

RF-Orchestra!™ Transmitter Installation and Operation System Description
July 2000 6880493G02-C 2-21
Power Amplifier
The PA is a linear RF gain module that amplifies the Exciter output to the required amplitude
for proper system operation (see Figure 2-11 and Figure 2-12). The PA module accomplishes
amplification in three distinct stages. These stages are similar in operation and are connected
serially.
The first stage is the predriver power amplifier (PPA). This stage receives its RF input from the
Exciter module located in the OCM and amplifies the RF to a higher level required for the
second stage, the driver power amplifier (DPA). The DPA output is split into three equal
amplitude signals for the final stage of amplification.
The final amplification step has unique requirements for high power RF generation. The final
stage uses three final power amplifier (FPA) modules in parallel. Each FPA amplifies the input
signal and outputs the RF signal into a combiner module. The combiner reconstructs a single
output and feeds it to the PA module output. The high power output level is then monitored
by a forward power detector and isolated from any external RF load variation by a circulator
with an internal high power load. The circulator output connector is the 7/16 DIN connector
of the PA module.
The power amplifier uses fans to provide front-to-rear airflow. Front-to-rear airflow provides
the heat sink with the lowest ambient air temperature available.