AR 10052412, Руководство по эксплуатации и обслуживанию

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Rev A 39
3. THEORY OF OPERATION
3.1 INTRODUCTION
The Model 5000A225C RF amplifier consists of a .01-225 MHz RF amplifier assembly. The RF amplifier
assembly consists of a pre-amplifier, driver amplifier module, a 4- way splitter to four 4-way splitters that drives
sixteen final amplifier modules. These sixteen final amplifier modules are combined through four 4-way
combiners, and a final 4-way combiner to yield a combined power of 5000 watts or more.
The control system consists of a Control/Fault Board, an Interface Board and remote interfaces for IEEE-488,
RS-232, USB, and Ethernet.
3.2 RF AMPLIFIER OPERATION
3.2.1 A1 Pre-amplifier Assembly
The Pre-Amplifier Assembly consists of two sub-assemblies: the A1 Pre-Amplifier Assembly and the A2 2W
Amplifier Assembly.
The Pre-Amplifier PWB Assembly consists of a variable attenuator circuit (U5), a gain stage (U10), a resistive
splitter (R21, R22, R25), and associated control circuitry. The overall gain of the pre-amplifier assembly is
approximately 32 dB at minimum attenuation. The power detector (U11) is used to sense the input RF power
and it increases the attenuation of the variable attenuator circuit if an input overdrive condition is detected.
The 2W Amplifier Assembly has two gain stages (U1 and Q1) that have a combined gain of approximately 30
dB. The output RF power is greater than 1W at the 1 dB compression point.
3.2.2 A2 125W Driver Assembly
The 125W Module Assembly consists of RF matching circuits, an RF transistor (Q1), a bias control circuit, and
a fault detection circuit.
The RF input is fed to a 4:1 balun transformer composed of T1 and T2. The output signal of the 4:1 transformer
is connected to the gates of Q1. The drains of Q1 are connected to a 4:1 balun transformer composed of T3 and
T4. Q1 has approximately 34 VDC applied to both drains at a total current of 8.5A. The RF stage has
approximately 21 dB of gain and an output compression point of 90W or greater.
The current through Q1 is monitored by U1. The output of U1 is fed to an op amp (U3) which has a reference
voltage on the non-inverting input. U3 compares the output of U1 to the reference voltage and generates an
error signal. This error signal varies the gate voltages of Q1 which in turn controls Q1’s current draw.
U5 is a comparator that monitors the output of U1 and generates a fault signal if the drain current varies outside
normal operating conditions. It also monitors the module temperature via a thermistor (R31) and generates a
fault signal if the module heatsink exceeds approximately 80
o
C.