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October 1961 Radio-Electronics
 [Table of Contents]
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Electronics,
published 1930-1988. All copyrights hereby acknowledged.
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Bell Telephone
Laboratories developed the T1 system (Transmission
System 1) in the late 1950s and early 1960s as a pioneering digital
transmission system that revolutionized telecommunications. It was the first
widely implemented digital carrier system, laying the foundation for modern
digital communication networks. As reported in this October 1961 issue of
Radio-Electronics magazine "News Briefs" column, theT1 system was still in
the development and installation phase, while public T1 service would begin the
next year. It facilitated 24 voice channels over an existing twisted pair of
copper wires, where before only a single call could be handled per pair. Also
mentioned was a shortage of TV sets as people clamored for the improved,
transistorized color versions. RCA announced the production of its one millionth
Nuvistor triode device. That, and more...
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News Briefs
 Now We Can Talk in Pulses
Phone users in the Newark-Passaic, N. J., area have unknowingly been taking part
in a synthetic speech experiment - every time they pick up their phones. Instead
of going out over the lines in original audio form. their words are broken down
into the language of computers; the transmission is by pulse code modulation.
 This is the first regular use of the system, which was developed by the Bell
Laboratories and demonstrated some years ago (Radio-Electronics, February 1948).
It has been named T-1 by the phone company. The speaker's voice is "sampled," tiny
bits being taken 8,000 times a second. The level of each sample is measured and
given a number in binary code, 1, 2, 4, 8, etc. up to 128. At the receiving exchange
the message is decoded and each binary number replaced by an audio pulse of the
correct strength. The result is a reconstituted signal not distinguishable from
the original in ordinary phone conversation.
Since a large number of pulse-coded conversations can be carried on the same
pair of wires, the new system is expected to be particularly useful in large cities
such as New York, where congestion below ground has often made it difficult to find
room for additional telephone conduit.
To install T-1, telephone companies will not have to dig up city streets. Instead,
using existing cable, they can connect terminal equipment in telephone buildings
at each end of the route, and repeater equipment in manholes or on poles along the
way.
Another advantage is that each repeater station reconstitutes the signal instead
of simply relaying it. If the message is distorted, but still intelligible, the
relay station, instead of amplifying it with the distortion, sends out a perfectly
formed new set of code pulses. Thus, as long as the pulses can all be interpreted
correctly, the signals will be as clear after several repeaters (they are spaced
about every mile along the transmission route) as after the first.
TV Set Shortage Coming?
Television receivers are selling faster than they are being manufactured, recently
warned Frank Mansfield, EIA's top market researcher. If production does not come
up, there may be an actual shortage of sets on the retail market in the late fall.
Mansfield estimates that at least 6,220,000 TV sets will be sold in 1961, a slight
increase over 1960. Inventories are lower than they have been since 1954. So unless
production is stepped up rapidly, there will not be enough sets on hand to meet
the year-end demand.
Gallium Arsenide Phototube Is Highly Sensitive
The Lansdale Div. of Philco re-ports a new gallium arsenide photo-tube that is
one or two orders more sensitive than conventional photo-diodes. It can also operate
in daylight without sensitivity degradation, unlike earlier units, and will work
at temperatures approaching 120°C.
The new phototube works at the red end of the spectrum, operating on both visible
and near-infrared light. It is designed to work between 0.4 and 0.9 micron, with
a peak sensitivity at 0.85 micron. Applications for the new photodiode, according
to Dr. Sutcliffe of the Lansdale Div., will include celestial body sensing, missile
tracking, space vehicle guidance, and applications in the computer and inertial
guidance fields. At its present price of $100 each, its use will be confined to
areas where cheaper and less sensitive photo-tubes will not work.
Silicon Rectifiers Replace Tube Types in Transmitters
Frank Marx, vice president in charge of engineering of the American Broadcasting
Co. has announced that silicon rectifiers will replace tube rectifiers in all its
owned and operated radio stations. Marx stated that 35% to 40% of the troubles that
caused disruption of service have been due to mercury rectifier arc-backs, and that
these are the largest single cause of serious transmitter troubles. The development
of high-voltage semiconductor rectifiers, he says, offers a means of eliminating
this source of transmitter trouble, and of "assuring our stations of continuous,
dependable service."
Briefer Briefs
Radio Corporation of America announces that its millionth nuvistor has been produced.
The small-size, low-noise tube is used especially in TV tuners to improve signal-noise
ratio in fringe areas. Nuvistors are now available in five types: two general-purpose
industrial triodes, a general-purpose industrial sharp-cutoff tetrode, and two high-mu
entertainment triodes.
Posted September 4, 2024
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