AR 10036390, Руководство по эксплуатации и обслуживанию

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Model 800A3B
Rev D 30
3.2.3 200W Modules
Refer to schematic 10021041. This module is a push-pull Class A amplifier which uses 4 transistors and a
unique output transformer to achieve high-output power. The input impedance-matching balun, T1, has one
side of its secondary connected to both “push” transistors and the other side connected to both “pull”
transistors. This assures that the push transistors have equal phase and amplitude signals and the pull
transistors have equal phase and amplitude signals.
The output transformer, T2, is essentially two push-pull transformers wound on a single core with its
secondaries connected in series. This configuration is capable of delivering twice the RF output voltage than
a single push-pull circuit could provide. The op-amps U2 and U4 maintain a constant average bias on each
transistor. The current-sensing IC U5 and the op-amp U3 work together to indicate over-current or under-
current conditions. S1 is a thermal switch used to prevent overheating of the amplifier.
3.2.4 Output combiner/directional coupler
Refer to Schematic 10019846. The outputs from the four amplifier modules are combined into one output in
the output combiner. The combiner operates in a zero-degree configuration. The single output then passes
through a dual directional coupler, located next to the combiner assembly, the output of which is routed to the
impedance transformer. The forward and reflected ports of the directional coupler are at a level of about –50
dB relative to the main output signal. The RF detectors for converting the amplifier’s Forward and Reflected
RF signals to usable DC signals are located in the relatively noise and heat free area behind the front display
panel, in an enclosure where the Automatic Level Control (ALC) and Fault boards also reside. The detected
signals are used by the ALC, fault detection/control circuits and by the Forward and Reflected power display
on the Digital Control Panel (DCP).
3.2.5 Impedance Transformer
Refer to schematic 10020367. The output power from the combiner/coupler module is directed to this
autotransformer in order to accommodate load impedances other than the standard 50 ohms. RF power can be
scaled down to a nominal 25- or 12.5-ohm impedance in order to deliver maximum power to a high current or
capacitive load. RF power can be scaled up as well, to a nominal 100-, 150-, 200-, or 400-ohm impedance in
order to deliver maximum power to a high voltage or inductive load. Any of these impedances are selectable
in any order from the User menu on the control panel.
3.3 POWER SUPPLY
Refer to Schematic Diagram Number 10036395, Interconnect Diagram, 800A3B . Main power to the unit is
supplied by single phase AC power within the proper range. In series with the line voltage is the 20A Main
circuit breaker CB1, located on the rear panel. This circuit breaker supplies line voltage to the contactor
located just behind the rear panel. The contactor is controlled by the front panel Power ON/Off switch and
interrupted manually by the three-position key-switch labeled Inhibit–Local–Remote . The contactor feeds
AC directly to the primary inputs of the main power supplies. When the main circuit breaker is on, AC power
is fed to the low voltage supply, PS1. Therefore, when the circuit breaker is turned on, the control panel and
basic low-power supplies are alive, and the amplifier is armed for Power On. At this time, the front panel
display is illuminated and the control circuitry is active.