the regenerative receiver was invented in 1912 and patented in 1914 by american electrical engineer edwin armstrong when he was an undergraduate at columbia university. it was widely used between 1915 and world war ii. advantages of regenerative receivers include increased sensitivity with modest hardware requirements, and increased selectivity because the "q" of the tuned circuit will be increased when the amplifying vacuum tube or transistor has its feedback loop around the tuned circuit (via a "tickler" winding or a tapping on the coil) because it introduces some negative resistance.