Marked: "Martian / Big Four / Newark, New Jersey / Pat. Pend.". A crystal radio detector with binding posts for headphone connections on top, posts for antenna and ground connections on bottom.
Marked: "Marconi's Wireless Telegraph Co., Ltd. / No. 180014 - London." Instrument is designed to receive code signals in the wavelength range of 200-2500 meters. Aerial tuning inductance normally ...
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