AR 10046836, Operating And Service Manual

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Model 500W1000C
28 Rev A
3.2.2 A2 Driver Amp and A6-A13 Final Amplifiers (Schematic
10045396)
Each A2 Driver amp and A6-A13 Final Amp consists of RF matching circuits, an RF transistor a DC current
control circuit, a DC switching circuit and a fault detection circuit.
The RF input is fed to a 4:1 transformer composed of T1, T2, and T3. The push-pull output signal of the 4:1
transformer is connected to the gates of push-pull connected Q1. The drains of Q1 are connected to a 4:1
transformer composed of T4, T4 and T6. The RF transistor , Q1, has approximately 22.5 VDC applied to the
drains at 4 amps current for the driver and 7 amps current for the finals. The RF stage has approximately 18
dB of gain for the finals and an output compression point of 50 watts or greater from final amplifiers A6-A13.
Voltage comparator U1 senses the presence of the –8 VDC. The output of U1 is high if the –8V supply is
–5.5 or less. The output of U1 pulls low when the –8 volts is present turning on Mosfet Q2 which supplies the
DC voltages to the drain of Q1.
The current through Q1 is monitored by U2. The output of U2 is fed to an op amp (U5) which has a reference
voltage on the non-inverting input and it compares the output of U2 to the reference voltage and generates an
error signal to vary the gate voltage of the RF transistor Q1 which controls the drain current.
U3 is a positive 5V regulator. It supplies DC to the current sense circuit, U2, the op amp, U5, and the fault
detection circuit, U6. SW1 is a thermal switch. It closes at a heat sink temperature of approximately 70
˚
to
protect the module in the event of an over-temperature condition.
3.2.3 A5 Eight-Way Splitter
The Eight-Way splitter splits the input signal into eight equal-amplitude, equal-phase signals. The amplitude
of each signal is 9–9.5 dB below the input sig nal when both outputs are terminated into 50Ω loads.
3.2.4 A14 Eight-Way Combiner
A14 is an Eight-Way combiner with impedance-matching. When the outputs of the eight final amplifiers are
fed to the eight-way combiner, the combined output will be approximately 9 dB above the output of a single
final amplifier.
3.2.5 A15 Dual Directional Coupler
A15 is a 50 dB dual directional coupler which is connected to the output of the A14 Eight-way combiner. The
coupler monitors the forward and reflected power.