The regenerative loop antenna can consist of a tuned signal winding on an open X frame with a feed back winding in close proximity. High effective gain is achieved, for example by placing this feedback winding in the drain circuit of a JFET (junction field effect transistor). An antenna of this type employing vacuum tubes was constructed by Vladimir Zworykin in the 1920s.
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Regenerative loop antenna Wikipedia(Text) CC BY-SA