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Several communication techniques are investigated in the first part of this paper: software radio, cognitive radio and encrypted communications. State of the art of research on agile and reconfigurable filters, passive as well as active, necessary for transceivers is then made and various tables for comparison are given. In the third part, a new theory for(More)
This article presents a new second-order state variable filter including two amplifiers. The centre frequency of the resulting filter, f<inf>0</inf>, can be easily controlled using the gains of the amplifiers. This leads to a frequency-agile filter, whose centre frequency can be controlled over a wide range, without incidence on the power consumption.(More)
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