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KF5JRV > TECH 23.04.16 13:36l 47 Lines 2501 Bytes #999 (0) @ WW
BID : 1922_KF5JRV
Read: GUEST
Subj: First Wireless Telephone
Path: IW8PGT<IZ3LSV<F1OYP<ON0AR<GB7CIP<VE3KPG<GB7LDI<N9PMO<N0KFQ<KF5JRV
Sent: 160423/1126Z 1922@KF5JRV.#NWAR.AR.USA.NA BPQ1.4.65
The First Wireless Telephone Communication April 1, 1880
On April 1, 1880 American inventor Alexander Graham Bell
and his then-assistant Charles Summer Tainter transmitted
the first wireless telephone message 213 meters on a beam of light
between the roof of the Franklin School and the window of Bell's
Washington, D. C. laboratory using the photophone.
"The photophone used crystalline selenium cells at the focal point
of its parabolic receiver. This material's electrical resistance
varies inversely with the illumination falling upon it, i.e., its
resistance is higher when it is in the dark, and lower when it is
exposed to light. The idea of the photophone was thus to modulate
a light beam: the resulting varying illumination of the receiver
would induce a corresponding varying resistance in the selenium
cells, which were then used by a telephone to regenerate the sounds
captured at the receiver. The modulation of the transmitted light
beam was done by a mirror made to vibrate by a person's voice: the
thin mirror would alternate between concave and convex forms, thus
focusing or dispersing the light from the light source. The
photophone functioned similarly to the telephone, except the
photophone used light as a means of projecting information, while
the telephone relied on a modulated electrical signal carried over
a conductive wire circuit".
Bell's and Tainter's invention, for which Bell received the master
patent in December 1880, was the forerunner of wireless
telecommunications and the far-advanced forerunner of
fiber-optic telecommunications.
According to Long & Groth, Bibliography of Early Optical (Audio)
Communications (2005) Bell's first paper on the
photophone, "Prof. A. G. Bell on Selenium and the Photophone,"
was first published in The Electrician No 5, 18 September 1880,
220-221 and 2 October 1880, 237. The complete paper also was
published in Nature (London) Vol 22, 23 September 1880, 500 - 503.
Thus the first complete publication appears to be the version
published in Nature.
Bell's longer paper "On the Production and Reproduction of Sound
by Light: the Photophone" was first published in American
Assocation for the Advancement of Science, Proceedings, Vol 29.,
October 1880, 115-136. This paper was widely reprinted in other
journals. "In these papers, Bell accords the credit for the first
demonstrations of the transmission of speech by light to a Mr A C
Brown of London 'in September or October 1878' ".
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