Milestone in Space Communication
February 1973 Popular Electronics

February 1973 Popular Electronics Table 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.

In 1971 the International Telecommunications Union (ITU), convened a meeting dubbed the World Administrative Radio Conference for Space Telecommunications (WARC-ST). The ITU was a specialized agency of the United Nations for telecommunications, with a membership of 140 nations. Satellite communications was barely a decade old, but already the need for international agreements on spectrum usage had become very apparent. Prior to the 1971 meeting, there was the 1963 Extraordinary Administrative Radio Conference held in Geneva, Switzerland. Amateur radio had its presence in the game acknowledged with further allocations for its members' OSCAR birds; six had been flown already. As of this writing there are about 20 OSCAR satellites still in operation. Amateur satellites take many forms these days, including the newest trend in CubeSat platforms with a well-defined set of specifications on dimensions (10 cm per side) and mass (≤1.33 kg, 2.9 lb) per cube. Launches are provided on a space available basis at a substantially discounted cost.

International Regulations That Will Affect Extraterrestrial Communications for Years

By Stanley Leinwoll

On January 1, 1973, a revised set of Radio Regulations assigning frequencies to all forms of space communication went into effect. Hammered out by some 750 delegates from 101 member nations of the International Telecommunications Union (ITU) in the summer of 1971, the Regulations will affect all space radio services, including television, telephone, telegraph, broadcasting, amateur, weather and meteorology, navigation, research, exploration, and radio astronomy.

The 1971 conference, convened as the World Administrative Radio Conference for Space Telecommunications (WARC-ST), and the frequency assignments it made, has been hailed by telecommunications experts as one of the most momentous ever held in the 106-year history of the ITU because it spells out the course of extraterrestrial communication for the remainder of this century.

The ITU is the specialized agency of the United Nations for telecommunications. It has 140 member nations responsible for drafting the rules and regulations that govern the allocation and use of the radio spectrum for international telecommunications.

In the more than 15 years since the Soviet Union launched Sputnik I on October 4, 1957, some 1000 spacecraft have left the surface of the earth to orbit our planet, on journeys to interplanetary bodies, and to carry men to the moon and back. In that, short time, space-borne scientific instruments have made and reported innumerable observations about space and the bodies contained within it. At present, for example, a U.S. spacecraft is hurtling toward a rendezvous with the giant planet Jupiter, after which it will become the first man-made object to leave our solar system.

Frequencies for Communication

Without frequencies with which to communicate, as well as for protection from interference from other services, the spacecraft leaving our planet would be of little value. Communication in one form or another plays a vital role in every satellite departing earth. Scientific data is sent back; astronauts and cosmonauts speak to their ground controllers, giving them essential data; photos and TV pictures of the moon and near planets are beamed to earth via communication links; beacon transmitters on board space-craft enable pinpoint tracking from earth stations; and even the most minute movements of satellites can be controlled remotely from earth by means of radio-controlled links.

Global communication has also come to rely more and more heavily on satellites. Intelsat IV, launched early in 1972, brought to 48 the number of TV channels open between the U.S. and other areas of the world. Communication satellites are currently the only means by which live TV can be transmitted or received from overseas locations. In addition, Intelsat IV can carry up to 6000 simultaneous two-way trans-oceanic telephone conversations under average conditions. This revolution in communication is dependent upon frequency assignments, and the 1973 Regulations make ample provision for frequencies to be used by such services.

In addition, several bands have been allocated above 12.75 GHz for development in the distant future.

Although broadcasting from satellites directly to home installations is not yet technically feasible, the revised Radio Regulations allocate frequencies to the broadcasting satellite service in anticipation of its eventual development. In the western hemisphere, such transmissions were authorized, with certain technical limitations (i.e., frequency-modulated video), to protect terrestrial TV stations on uhf TV channels 39 through 66. This will permit the development of broadcasting satellites (probably not before the end of this century) on existing TV channels so that advantage can be taken of the large number of receivers now available in this range.

Another broadcasting allocation was made in the 2500-2690-MHz range to permit broadcasting to special receiving installations at schools and in community centers, primarily for educational purposes. The U.S. and India jointly plan to test community broadcasting from a satellite during 1974.

The new Radio Regulations also allocate 11.7-12.2 GHz (12.75 GHz in Europe and Africa) to the broadcasting satellite service. Since there are no TV stations operating in this range at the present time (and no receivers), this will eventually require the development of an entirely new TV system. This is probably the first step in the evolution of 21st century television.

Additional broadcasting allocations were made in several higher bands, but they amount to stake-outs for development in the very distant future.

Radio Amateur Frequencies

A new satellite service was defined at the 1971 ITU conference. It was called the earth exploration satellite service. Satellites in this service, which include those employed for meteorological uses, will gather information relating to the characteristics of earth and its natural phenomena. These satellites should make possible more accurate weather forecasting and are expected to provide an accurate cataloging of the earth's resources. Allocations in 10 discrete bands from 137MHz  to 22 GHz were assigned to this service.

There were some additional allocations made for manned and unmanned satellites in the space research service. These are channels used to transmit telemetry data back to earth and for beacon and tracking signals. Some 24 different bands were allocated to this service on frequencies ranging from 2501 kHz  to 8500MHz . Still other assignments were made above 10 GHz.

Frequencies for Other Services

A standard frequency for satellites has been established at 400.1MHz  (±25 kHz), and time signals will be transmitted from satellites on two additional standard frequencies -4202MHz  and 6427MHz , ±2MHz .

The 1973 Regulations envision greater utilization of satellites for navigational purposes and the eventual development of satellite systems that will permit aircraft and ships to communicate via satellites. Some 13 bands have been assigned to the navigational service for these purposes.

In addition to signals transmitted from man-made space objects, there are other radio signals that originate deep in space. Among these are natural radio emissions originating in the sun, the planets, and stars (and other objects such as pulsars and quasars). To protect these extremely weak signals that reach our planet, the Radio Regulations set aside a large number of narrow slots throughout the radio spectrum for use in the radio astronomy service. Use of the frequencies set aside for this service is prohibited from spacecraft, and restricted use by terrestrial stations has been incorporated into the Regulations. Beginning in 1973, radio astronomers will be assured that signals heard in the bands set aside for their use are not man-made.

The 1973 Regulations that are an out-growth of the 1971 conference represent a milestone in the history of telecommunications. Assignments made by the conferees will be used for the remainder of this century.

Posted February 21, 2020