AR 25U1000, Operating And Service Manual

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Rev A 7
3. THEORY OF OPERATION
3.1 INTRODUCTION
The Model 2.5U1000 RF amplifier consists of a single .01-1000 MHz RF amplifier assembly.
The power supply section consists of an AC input filter, a circuit breaker, +5V, +15V, and -15V power supply
and a +24V power supply.
2.5U1000 Block Diagram, 10041313, Rev A
3.2 AMPLIFIER SECTION
3.2.1 A1 2W Pre-Amplifier Assembly (Schematic No. 10041189,
10041352, 10041055)
The 2W Pre-Amplifier Assembly consists of 3 sub-assemblies: the A1 Pre-Amplifier Assembly, the A2 Switch
Assembly, and the A3 2W Amplifier Assembly.
3.2.1.1 A1 Pre-Amplifier Assembly (Schematic 10041189)
The Pre-Amplifier PWB Assembly consists of a variable attenuator circuit (Q1-Q4), a gain stage (U4), a
resistive splitter (R13, R14, R16), an RF power detector (U6), and associated control circuitry. The overall gain
of the pre-amplifier assembly is approximately 6-8 dB at minimum attenuation. The power detector (U6) 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.
3.2.1.2 A2 Switch Assembly (Schematic 10041352)
The Switch Assembly is made up of a variable attenuator circuit (Q1-Q4) and associated control circuitry. The
switch can either be in an on or off state depending on the Inhibit input signal (E4). In the off state, when E4
is pulled low, the switch will reduce the amplifier gain by approximately 40 dB.