English: Parabolic antennas used in a 1931 experimental microwave relay link across the English Channel, one of the earliest experiments in microwave communication. The 10 foot (3 m) diameter dishes transmitted voice, telegraphy, and facsimile images over 1.7 GHz (18 cm wavelength) bidirectional microwave beams 40 miles between Dover, England and Calais, France. The microwaves were generated by a miniature Barkhausen-Kurz tube located at the focus of the transmitter dish behind the hemispherical shroud visible in the center; an identical tube at the receiver amplified the received signal. The radiated power was about one half watt. In this image the dish in the foreground is the transmitter, while the receiver dish in the background was located behind the transmitter to avoid interference. The demonstration was sponsored jointly by the International Telephone and Telegraph Company (ITT) and the Laboratoire du Materiel Telephonique of Paris, managed by G. H. Nash for the English and E. M. Deloraine for the French. Although this was planned as the prototype for a commercial microwave system, the sponsors found they could not compete with cheap underwater telephone cables. A commercial 300 MHz link was built in 1935, the first microwave relay system. Note man next to foreground antenna for scale.

Caption: "Two similar parabolic mirrors serve as transmitter and receiver at each end of the cross-Channel link, the receiver placed back of the transmitter to avoid interference."