4 Ionospheric Bubble u

Long-Distance VHF created for

Communication

Scientists at Stanford Research Institute have demonstrated a new technique which can increase the range of VHF radio and television signals 20 times or more. They have shown that a temporary man-made “bubble” can be produced in the ionosphere which reflects VHF signals back to earth, and thus extends their range to a point 1000 mi or more from the

tenna System located near Platteville, Colo. to heat a ”bubble” or bulge Radio scientists from Stanford Research Institute (SRI) used this an-

in the ionosphere, about 100 mi above the earth’s surface. Radio and television signals, bounced off the bubble, travel up to 20 times their normal range.

originating transmitter. Normally, these signals pass through the ionosphere and are limited to a range of about 50 mi along a direct line from transmitter to receiver.

The bubble is produced by heating the ionosphere with a beam of short-wave radio signals from a ground-based “heating transmitter.” The principle is similar to that of a microwave oven. The bubble is typically about 100 mi in diameter and 10 mi thick, directly above the transmitter. It is invisible to the eye, but can be photographed with an infrared camera. The actual reflectors in the bubble are electronic irregularities

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Phil Fialer (left), Larry Sweeney, and Victor Frank check out graphic recordings of signals picked up after being bounced off the "bubble."

bubble to appear in the ionosphere. Behind them is a photo of some of the equipment that caused the

produced by heated electrons. When the transmission is com- pleted, the heating transmitter is turned off and the reflecting irregularities disappear, leaving no pollution or ecological dis- ruptions of any kind.

The scientists envision the biggest commercial application of the new technique as point-to-point communication of telephone, teletype, and facsimile signals, as well as mobile radio, especially in countries that lack modern communica- tions. The bubble will be most useful for reflecting signals in the VHF band, particularly public service radio (police, fire department, and taxicabs) and mobile radiotelephones. The new technique is not particularly attractive for broadcasting commercial FM and TV to home because signals reflected from the bubble are weaker than those normally used in broadcasting and suffer some fading distortion.

The heating transmitter required to produce the com- munications bubble is a standard high-power (500 kW) short- wave transmitter connected to a special antenna. The cost of building such a facility is estimated to be between $2 and $4 million, but the most economic way to obtain heating trans- mitters would be to convert existing short-wave broadcasting transmitters. Eight of these are in the U.S. and would require no additional staff to be operated as heating transmitters, although they may not be located in the correct position to allow transmission between any two desired points. Because of the effect of the earth's magnetic field, the size, shape, and location of the area served would vary with the latitude and longitude of the bubble, and therefore with the location of the heating transmitter. For example, the bubble could be used to transmit signals within a larger geographic area at the equator than in the U.S. This is one reason why it is felt the technique would be of particular value to underdeveloped countries.

SRI's research team, directed by Dr. Philip Fialer and Dr. L. E. Sweeney, included Dr. 0. G. Villard, George Carpenter, Victor Frank, and Dr. Robert Leonard. The program was sponsored by the Defense Department's Advanced Research Projects Agency through the Office of Naval Research. While the demonstration of the bubble's long-distance reflecting ability was the first of its kind, Soviet scientists at Gorki in the USSR are also studying the phenomenon. An international meeting at Lima, Peru next summer will consider the implica- tions of the phenomenon.

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ICC '75 Planned for San Francisco Sun Francisco, California-Plans for the eleventh annual

International Conference on Communications (ICC '75),sched- uled for June 16-18 at the San Francisco Fairmont Hotel, are well underway. Promising to be the largest conference of its kind held to date, ICC '75 will feature daily technical sessions plus some 65 exhibits of electronic communications equip- ment and related gear.

Sponsored by the IEEE Communications Society Confed ence Board, ICC '75 is under the chairmanship of C. George Griffith, GTE Lenkurt. The theme for this year's conference is "International Understanding Through Communications."

According to the technical program chairman, Dr. Philip Fire of GTE Sylvania, the ICC '75 technical sessions will span the entire spectrum-from wire transmission through satellite communications. While the topics and speakers are still being finalized, Dr. Fire did preview some of the topics:

Wire. What's New in Analog Systems?; The Evolving Digital Network; Application of Delta Modulation to Telephone Transmission; The T4 System.

Data. PCM Systems in Europe; Picture Coding; Facsimile Transmission; Evaluation and Simulation of Communication System Designs; Scintillation Effects.

Switching. TSPS No. 1-The Remote Trunk Arrangement; Digital Switching and Transmission Interfaces; Design and Control of Packet Switches.

Radio. Digital Radio Systems; Digital Transmission Over Tropospheric Paths; Paging and Alarm Systems; Multipoint Distribution Systems.

Satellite. The Canadian TELSAT TDMA System; Very Wideband Communication Systems; Modulation Techniques For Space Communications; Optical Communication Systems.

Other. Error-Control Techniques; Charge-Coupled Devices in Communications Applications; TIC System Electronics.

In addition to the above broad range of communications topics, ICC '75 will also include pertinent reports from various IEEE groups. The group reports will cover: Speech Pro- cessing Techniques; Results of the ATS-6 Satellite Experi- ments; Microwave and Millimeter-Wave. Devices and Tech- niques; Electromagnetic Compatibility in Communications.

As a special tutorial bonus, Dr. Andrew J. Viterbi, Vice President of Linkabit Corporation will present a 6-hour lecture series on "Coding and Modulation for Coherent, Non-Coherent and Multiple Access Channels." The first session of the tutorial will be devoted to the basic concepts and techniques of con- volutional coding with application to Gaussian channels, while the second session will concentrate on non-coherent, multipli- cative noise, and multiple-access channels.

Exhibits chairman Fred C. Hill of GTE Lenkurt reports that the 65 available exhibit spaces are rapidly being booked, with a number of companies purchasing multiple booths to show their wares. Products to be displayed include microwave, multiplex, data, and special-service equipment, as well a$ instrumentation, specialized components and other tele-. communications gear.

For information on exhibiting, contact Fred Hill or Bob Smeland, GTE Lenkurt, (415) 591-8461. T o secure advance program information and registration materials, write:

ICC '7 5 P.O. Box 77191

San Francisco, Calif. 94107 0