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Applied Systems Engineering,
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OPHIR RF,
R.A. Mayes,

NOTES ON AMPLIFIERS USED IN ELECTROMAGNETIC COMPATIBILLITY TESTING
In the field of EMI-EMC, amplifiers are used for two main purposes:
1) to increase the sensitivity of devices such as spectrum analyzers and radio receivers These are known as pre-amplifiers, or "pre-amps."
2) to increase the power produced by a signal generator in order to test the susceptibility (immunity) of a device. These are known as POWER AMPLIFIERS. Radio Frequency (RF) power amplifiers are used for susceptibility (immunity) testing in accordance with US Military Electromagnetic compatibility standards such as MIL-STD 461E and its predecessors, such as MIL-STD-461C, MIL-STD-461D, MIL-STD-462 as well as E3 , Electromagnetic environmental effects. Power amplifiers are also used in the commercial CE Mark testing required by European Community Standards such as 89-336-EEC.
The term "TWT AMPLIFIER" stands for Travelling Wave Tube Amplifier, a type of power amplifier used in the microwave range.
It is relatively easy to build an amplifier that works well over a narrow range of frequencies. It is harder to build one that works well over a very wide range. This is why BANDWIDTH is related to cost. For power amplifiers, output power is also related to cost. Even though there is plenty of power available at any a.c. power outlet, applying this power over a broad range of radio frequencies in a rugged and reliable instrument presents several engineering challenges. These web sites provide a good overview of the Radio Frequency (RF) amplifiers used in the EMI-EMC field, as well as the general field of E3 , Electromagnetic environmental effects.

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