We have already announced the design method of the passive attenuator to prevent a high voltage which induced at a crane hook of a large crane used near a medium wave radio broadcasting antenna. But it is very difficult fundamentally to microminiaturize this passive attenuator.
In this time, we developed an active attenuator that possible to miniaturize where a negative resistor or a fourterminal amplifier is included. From the result analyzing this crane equipped with an active attenuator theoretically, we show the design method of the active attenuator. In this paper, first the equivalent circuit of the crane equipped with the active attenuator as a receiving antenna is induced. And we show that the attenuated characteristics of the active attenuator by the model experiment accords with the theoretical attenuated characteristics which employ an equivalent circuit under the same condition.
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