Electronics World articles Popular Electronics articles QST articles Radio & TV News articles Radio-Craft articles Radio-Electronics articles Short Wave Craft articles Wireless World articles Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors LinkedIn Crosswords Engineering Humor Kirt's Cogitations RF Engineering Quizzes Notable Quotes Calculators Education Engineering Magazine Articles Engineering software RF Cafe Archives Magazine Sponsor RF Cafe Sponsor Links Saturday Evening Post NEETS EW Radar Handbook Microwave Museum About RF Cafe Aegis Power Systems Alliance Test Equipment Centric RF Empower RF ISOTEC Reactel RF Connector Technology San Francisco Circuits Anritsu Amplifier Solutions Anatech Electronics Axiom Test Equipment Conduct RF Copper Mountain Technologies Exodus Advanced Communications Innovative Power Products KR Filters LadyBug Technologies Rigol TotalTemp Technologies Werbel Microwave Windfreak Technologies Wireless Telecom Group Withwave RF Cafe Software Resources Vintage Magazines RF Cafe Software WhoIs entry for RF Cafe.com Thank you for visiting RF Cafe!
Innovative Power Products Passive RF Products - RF Cafe

Exodus Advanced Communications Best in Class RF Amplifier SSPAs

Innovative Power Products Passive RF Products - RF Cafe

Please Support RF Cafe by purchasing my  ridiculously low−priced products, all of which I created.

RF Cascade Workbook for Excel

RF & Electronics Symbols for Visio

RF & Electronics Symbols for Office

RF & Electronics Stencils for Visio

RF Workbench

T-Shirts, Mugs, Cups, Ball Caps, Mouse Pads

These Are Available for Free

Espresso Engineering Workbook™

Smith Chart™ for Excel

Anritsu Test Equipment - RF Cafe

"Over the Horizon" Transmission
August 1955 Popular Electronics

August 1955 Popular Electronics

August 1955 Popular Electronics Cover - RF CafeTable of Contents

Wax nostalgic about and learn from the history of early electronics. See articles from Popular Electronics, published October 1954 - April 1985. All copyrights are hereby acknowledged.

Here is a brief article about implementing over−the−horizon (OTH) transmissions for television and phone signals. It appeared in a 1955 issue of Popular Electronics magazine, only a decade after the end of World War II and at the tail end of the Korean War, when the majority of households had at least one TV set. Being able to exploit OTH would eliminate numerous relay towers in−between which are not only expensive, but often are difficult to locate due to property acquisition issues. The article suggests the possibility 200 mile spacing between towers.

A transmission tower 1,000 feet tall looking out over flat land sees the horizon at about 38.7 miles, so another 1,000-foot tower another 38.7 miles in line from the horizon would give 77.4 miles total between towers, but that assumes perfect line-of-sight propagation without refraction, reflection, etc.

To verify the above number, go here and enter "Distance to the object" = 77.4486 miles, "Eyesight level" = 1000 feet, "Distance to horizon" = 38.7 miles. The result will be "Obscured object part" = 1000 ft. QED

See the Bell Telephone Laboratories - Over-the-Horizon Communications full-page advertisement in the October 1955 issue of Radio & Television News magazine. 

"Over the Horizon" Transmission

"Over the Horizon" Transmission, August 1955 Popular Electronics - RF CafeSuper-powered transmitters beam TV and phone signals up to 200 miles without help from relay stations

Direct television and multichannel telephone transmission through space for as much as 200 miles - without relay stations and at ultra-high frequencies - is now a reality, according to announcements by Bell Telephone Laboratories and the Massachusetts Institute of Technology. Video and audio information can both be sent "over the horizon" on u.h.f, channels in an extension of a transmission technique recently applied to the continental defense system.

Over-the-horizon transmission means that longer communications bridges are possible over water and rugged terrain. In the present microwave radio relay network across the United States, relay stations are only about 30 miles apart.

Standard AM radio broadcasting employs waves that follow the earth's curvature. But waves used in television and telephone relays were presumed to travel in a straight line. For many years, "line of sight" transmission between antennas placed on towers on the horizon (about 30 miles apart) was thought to be the only practical means of transmitting by radio the wide bandwidth needed for television and multichannel telephone service.

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.

Scientists knew that ultra-high frequencies traveled "over the horizon" under certain conditions but believed them to be too weak and undependable for practical use. In the course of investigating occasional interference attributed to these waves, however, the scientists discovered that many actually overshot the relay towers they were aimed at and arrived at farther points with remarkable consistency.

The next step was to provide reliable long-distance transmission "over the horizon." Engineers did this by erecting larger antennas and using higher power than is employed in the conventional microwave system. Thus, they put to use the weaker signals that drop off a straight radio beam beyond the horizon and are reflected or scattered to distant points by the atmosphere.

The effect of the new system is very much like that of a powerful searchlight which casts a beam in a straight line. A searchlight aimed at the sky can be seen from the ground miles away, even when the searchlight is behind a hill. This is possible because some of the light is reflected and scattered by the atmosphere.

In order to make use of over-the-horizon transmission, 10-kw transmitters and 60'-diameter antennas are being employed, representing 20,000 times the power and 30 times the antenna area used in the present transcontinental microwave system. It was found necessary to employ the lower frequencies (in the u.h.f. band) to develop with available equipment sufficient power to attain a satisfactory degree of reliability.

Even after scientists learned that transmission was possible "over the horizon," they were not certain that this medium would support the broad band of frequencies needed for multichannel telephone or television transmission. In the fall of 1953, they found that they could transmit 12 voice channels "over the horizon." Television was first successfully transmitted this way in 1954 between Bell's Holmdel, N. J., laboratory and the M. I. T. Round Hill Research Station near New Bedford, Mass., a distance of 188 miles.

Bell and M. I. T. scientists emphasize that this success with over-the-horizon transmission will probably result in a supplement to - rather than a replacement of line-of-sight radio relay systems.

Over-the-horizon signals are not to be confused with a similar type of transmission known as "ionospheric scatter," which is useful in long-distance transmission of telegraph signals at relatively low frequencies. Unlike ionospheric signals, the over the-horizon technique provides signals that are useful for the wide bandwidths required for a television picture or by many telephone channels.



Posted October 7, 2022
(updated from original post on 8/24/2011)

Anritsu Test Equipment - RF Cafe
Anatech Electronics RF Microwave Filters - RF Cafe

Amplifier Solutions Corporation (ASC) - RF Cafe