The circuit was constructed using a few components that is powered by a 9 V battery for sensing the presence of bugs transmitting within the frequency modulation range. Frequency Modulation (FM) – ...

Fig. 1: A simplified linear detector circuit of the Bose FM multiplex detector from the patent documents. Fig. 2: John Bose enjoys a hearty meal in the Alpine FM transmitter building in July, 1939.

Home Data Center “Crowdsourcing spin detection” — http://ping.fm/aGjZd by Mark Gibbs ...