Video Telephone: The American Telephone and Telegraph Co. demonstrated its new video telephone set and announced that commercial service would be inaugurated in the early 1970s. A trial installation of 40 sets at various locations in New York and Pittsburgh was announced for September 1968. Commercial service using an earlier version of the set has been available among three central locations in New York, Chicago, and Washington.
There are two common methods of eliminating clutter. In one, called noncoherent moving target indication, the target echoes are identified by the beat that occurs between their frequency and the frequency of the ground return received with them. Since the Doppler shift is very slight, the period of the beat frequency is many times greater than the width of the radar's pulses. As a result, the beat between a particular moving target's echoes and the ground return is evidenced by a change, from one repetition period to the next, in the amplitude of the return received from a given range. To detect moving targets, the video output of the receiver is delayed by exactly one repetition period, and the undelayed video is subtracted from the delayed video.
Telephone Services. The first British telephone schange was opened in 1879 in London by The elephone Company, Ltd., but in 1880 the high >urt ruled that private telephone services were i infringement on the post office's monopoly ?hts in telegraph. However, it was decided grant private developers licenses that would pire at the end of 1911.
The post office's first telephone exchange as opened in 1881 at Swansea.
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