(OTH) radio signal transmission was a relatively new phenomenon when this
advertisement by Bell Telephone Laboratories appeared in a 1955 issue of
Radio & Television News magazine. It was a big year for OTH. The discovery
and exploitation of it was originally the domain of Ham radio operators who were
allocated the believed-to-be useless spectrum that supports it. However, once
the government realized the important ramifications of OTH communications
(radar, voice, video), military research organizations quickly initiated efforts
to exploit it for national defense and security purposes, then classified much
of the science. In this same year as this advertisement an article by Bell Labs
about OTH technology entitled, "'Over the Horizon'" Transmission"
appeared in Popular Electronics magazine, saying how previously it was
thought the only practical means of transmitting by radio the wide bandwidth
needed for television and multichannel telephone service was line-of-sight
(LOS). "This was disproved after years of research at M. I. T. and Bell
Telephone Laboratories. The Bell Laboratories' research stemmed from Bell's
success with transcontinental microwave systems for carrying telephone
conversations, radio and television programs from coast to coast, and their
continued interest in radio propagation. The M. I. T. interest was stimulated by
work for the Government in radar and overseas broadcasting."
Bell Telephone Laboratories Ad
Highly schematic drawing illustrates the
possible distribution of energy in ultra-high-frequency "over-the-horizon" transmission.
The effect is similar to that of a powerful searchlight whose beam points into the
sky. Light can be seen miles away from behind a hill even when the searchlight lens
Something new on the telephone horizon
Telephone conversations and television pictures can now travel by ultra-high-frequency
radio waves far beyond the horizon. This was recently demonstrated by Bell Telephone
Laboratories and Massachusetts Institute of Technology scientists using "over-the-horizon"
wave propagation, an important recent development in the radio transmission field.
This technique makes possible 200-mile spans between stations, instead of the
30-mile spans used for present line-of-sight transmission. It opens the way to ultra-high
frequencies across water or over rugged terrain, where relay stations would be difficult
In standard microwave line-of-sight transmission, stations are so spaced that
the main beam can be used. But now, with huge 60-foot antennas, and much higher
power, some signals drop off this main beam as it shoots off into space. These signals
reach distant points beyond the horizon after reflection or scattering by the atmosphere.
The greater power and larger antennas of the "over-the-horizon" system permit recapture
of some of these signals and make them useful carriers. The system will be a valuable
supplement to existing radio relay links.
This experimental 60-foot antenna (rear view) photographed at Bell Laboratories
in Holmdel, New Jersey, is designed for study of "over-the-horizon" phenomena.
Bell Telephone Laboratories
Improving telephone service for America provides careers for creative men in
scientific and technical fields.
Posted November 16, 2020