December 1948 Popular Science
[Table of Contents]
Wax nostalgic about and learn from the history of early
electronics. See articles from
Popular
Science, published 1872-2021. All copyrights hereby acknowledged.
|
Maybe the term "time domain
reflectometry" had not been coined when this
Bell Telephone Laboratories (Bell Labs) advertisement appeared in a 1948 issue
of Popular Science magazine. Or, maybe the creators figured Popular
Science readers, while generally a more technically-oriented group, might not
possess the depth of understanding needed to appreciate the phrase. At the time,
use of coaxial cable transmission lines for carrying telephone calls was fairly
new, although Bell began using some
coaxial
cable in 1927. A decade earlier, prior to great advances in high frequency communications
during World War II, twisted pairs of solid conductors were sufficient to handle
traffic. They did a good job, but each twisted pair carried only a single circuit
operating at audio frequencies. That is why telephone cables were so large in diameter
- they could be holding hundreds of twisted pairs. Coaxial cable signals can handle
hundred or thousands of channels by modulating across a very wide bandwidth. Installation
and maintenance of coaxial cable is much less than with a multiconductor cable.
I remember seeing technicians on a ladder or in a bucket making up splices on hundreds
of twisted pairs when a line went down or a new tap was being installed.
Bell Telephone Laboratories Ad
He asks an echo
Radar sends out pulses of electric waves which, reflected from a target, return
to reveal the target's location.
Likewise, the apparatus pictured above sends electric waves over a coaxial telephone
cable. Minute irregularities reflect the waves back to their origin; the echo makes
a trace on an oscilloscope screen and so tells where to look for the trouble.
Telephone messages need smooth "highways" over which to travel across country:
circuits able to transmit every talking frequency, without distortion.
Television needs even smoother highways and at many more frequencies. So Bell
Laboratories devised this method of spot-testing the cable over the entire frequency
band needed for telephone or television. It is so delicate that any possible interference
with transmission is detected at once. Its use makes sure that every inch of highway
is clear.
This is another important example of how Bell Telephone Laboratories constantly
develop finer communications for the nation.
Bell Telephone Laboratories
Exploring and inventing, devising and perfecting for continued improvements and
economies in telephone service
Posted May 20, 2024
Bell Telephone
Laboratories Infomercials |
|
|
|