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7.5 PA Output Combiner Network
The PA outputs are then combined by a 14-way Gysel combiner to provide a combined
output from each cabinet. The combiner contains isolation resistors attached to a heat
pipe. These loads provide isolation between module ports, allowing shut off and
removal of any module without affecting the performance of the remaining modules.
Under normal operation with all modules installed and operating, these loads absorb
minimal power. Should one or more of the modules be disabled, shut off, disconnected
from its power connector or removed from the cabinet, the load resistors will absorb
some power.
The amount absorbed is slightly higher when the modules are disconnected and
removed than when they are merely shut off. This is because removing a module
presents an open circuit to that combiner port, as opposed to merely disabling the
module, in which the combiner sees the isolation resistors present in the module’s
output combiner.
The amount of power absorbed by any single load is highest when a single module is
removed. The total amount of power absorbed by all the resistors is highest when half
of the modules are removed.
Figure 7-2 Gysel Combiner
7.6 Gysel Combiner Theory
The Gysel combiner, shown in Figure 7-2, is another modification of the Wilkinson
combiner. The Gysel combiner can combine any number of amplifiers, being limited
only by the availability of the correct impedance transmission line used to connect each
amplifier to the output load (RL).