 The name "superheterodyne" was a contraction of "supersonic heterodyne", to distinguish it from receivers in which the heterodyne frequency was low enough to be directly audible, and which were used for receiving "continuous wave" (CW) Morse code transmissions (not speech or music).After the war, in 1920, Armstrong sold the patent for the superheterodyne to Westinghouse, who subsequently sold it to RCA.The increased complexity of the superheterodyne circuit compared to earlier regenerative or tuned radio frequency receiver designs slowed its use, but the advantages of the intermediate frequency for selectivity and static rejection eventually won out; by 1930, most radios sold were 'superhets'.