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WORKING PAPER INTRODUCTION Most governments broadcast audio programs outside their sovereign borders. In the United States the Voice of America (VOA) of the United States Information Agency (USIA) is the Federal government agency charged with broadcasting over-the-air radio programs related to U.S. interests and activities.] The U.S. Board for International Broadcasting (BIB) oversees Radio Liberty (RL) and Radio Free Europe (RFE), which act as surrogate radio broadcasters for people who reside in the Soviet Union and the Eastern Bloc countries, respectively. VOA transmits audio programs to audiences throughout most of the world. The transmissions originate in the United States and are picked up by people using fixed and portable receivers. VOA audio programs include talk and music presentations. Some programs are broadcast by radio transmitters that operate in the medium frequency (MF) portion of the radiowave spectrum at frequencies of 0.3-3.O MHz. The bulk of VOA programs are broadcast in the high-frequency (HF) shortwave portion at frequencies generally confined to 3.0-30.0 MHz. VOA audio programs broadcast at HF are di rected to l i steners located great distances from the VOA broadcasting transmitter sites. With the exception of the lowest part of the ME band and even lower frequencies, the range of radio signals transmitted via the Earth's atmosphere and surface or ground-wave propagation that can be easily and usefully received is limited to a few hundred miles from the transmitter. If properly directed upward and forward by the transmitter's antenna, a much greater range may be obtained by using HF shortwave signals. This increase in range is caused by sky-wave propagation--the HF shortwave signals usually are reflected or refracted downward toward the Earth's surface from one or more layers of ionized gas normally present in the upper atmosphere. The quality of the HF shortwave signal received and the ease and reliability of that reception depend upon l. The amount of radio-frequency power radiated by the broadcasting transmitter, several transmitters may be used to broadcast the same program simu] taneously. 2. The effective absolute gain of the transmitting antenna in the direction of the intended audience. 3. The surface distance from the transmitter to the listening audience. Other UST A off i ces are respons i b l e for add i t i on al met hod s of disseminating information, including the distribution of books and television programs, and the sponsoring of international visitor and ect u re r exc h ange s. 2 WORKI NO PAP ER
WORKING PAPER 4. The electromagnetic characteristics of those portions of the ionosphere and the Earth's surface involved in the propagation of the transmitted signal at the transmitter's radio frequency during the broadcast) ng i nterval . 5. The character and intensity of natural and commercial-industrial electrical noise generated external to the listener's receiver. 6. The character and intensity of any other signals radiated simultaneously on, or very close to, the desired signal's frequency, and the electromagnetic characteristics of those portions of the ionosphere and the Earth's surface involved in the propagation of those other signals toward the recei ver. 7. The characteristics of the listener's receiver, including the absolute gain of the antenna at the received frequency in the direction of the desired arriving signal, and the antenna's relative gain in the direction of arriving commercial-industrial electrical noise, and any other natural or manmade signals. In light of these operating circumstances and the limited number of frequencies that by international agreement are available to the more than lOO countries conducting HE shortwave broadcasting, broadcasters must now use sophisticated and costly transmitter plants and operating procedures to provide service that wild attract and retain listeners. During the past two decades, many governments have placed greater importance on their worldwide audio broadcasting activities. There has also been a large increase in the number of countries engaging in HF shortwave broadcasting. These developments have fostered a trend toward the use of greater transmitter effective radiated power_ (EIRP), a growing practice of broadcasting the same program simultaneously on more than one frequency, and a more sophisticated, more dynamic movement among transmitting frequencies and the directions that signals are radiated throughout the preferred listening hours of the day. Average EIRPs now exceed lOO million watts and the same program may be broadcast on as many as six frequencies at the same time. These efforts are made to accommodate to so~ar-reJated diurnal, seasonal, annual, and 11-year cycles of change in the ionosphere's radiowave propagation characteristics. Efforts are also made to retain audience share in the face of growing competition by other broadcasters and other media. These trends burden many broadcasters, who face increased financial costs, increased need for more effective transmitting sites, increased professional engineering and operating demands, and increased interference to their signals by the signals of other broadcasters that arrive 2. Radio frequency power X antenna gain relative to an isotropic radiator. - 3 WORKING PAPER
WORKING PAPER simultaneously in their desired audience areas on essentially the same or closely nearby frequencies. Two unfortunate results of this large, growing overpopulation within the HF shortwave broadcasting bands agreed upon by the countries using the International Telecommunications Union "offices" are the use of frequencies within these bands by countries that are not part of such agreements, and the use of frequencies outside of these bands. There are now an average of two to three broadcasting transmitters competing for each useful signal channel during the more popular listening hours. This situation is further exacerbated by a few governments that routinely contrive to deny some or all of their citizens the ability to receive signals broadcast to them by other countries. They do so by radiating intentionally harmful interference ~ jamming signals) on the frequencies used by other broadcasters. The radiowave propagation characteristics of the ionosphere often allow jamming signals to interfere with the reception of programs broadcast on these frequencies within countries located far from the areas being jammed. These circumstances and trends have caused a sharp increase in the level of nonnatural interference to HE shortwave signals broadcast over much of the world, and growing problems in allocating and using available frequencies. The increased use of satellite communications circuits and networks to provide long-hau] fixed and marine mobile communications services has reduced the use of the HF portion of the radio spectrum for these other purposes. Yet there is a large demand for these vacated frequencies for national, domestic broadcasting and other services. There is also little immediate likelihood that these strong basic shortwave trends can be arrested, let alone reversed. This situation has become so serious that the utility of some services provided by the largest and most sophisticated broadcasters is being questioned. Many countries with more modest financial resources and/or without long-established broadcasting spectrum occupancy positions are increasingly frustrated and resentful about their apparent inability to obtain what they judge as their fair share of a valuable and increasingly limited global commodity. Their inability to obtain clear and affordable HF broadcasting air space adds to existing international political strains. Today, and in this context, VOA and RFE/RL HF shortwave broadcasting operations are triply disadvantaged: 1. Other HF shortwave broadcasters are growing in numbers and sophistication, competing for the attention of listeners that VOA and RFE/RL are expected to serve. 2. ~ imi ted broadcast) ng p ~ ants have not al ~ owed VOA and RFE/RL to keep up with increased foreign capabilities, despite the fact that national security considerations require VOA and RFE/RL to reach larger and additional audiences. 4 WORK] NG PAP ER
WORKING PAPER 3. Until recently the VOA and RFE/RL have not had the funds to conduct appropriate research and development (R&D) activities. These activities could allow modifications in plant and operations designed to allow VOA and RFE/RL to keep up with and perhaps outpace other countries. The VOA and RFE/RL clearly need a major increase in their broadcasting capabi l i ti es. The recognition of this need began to gain credence a few years ago. During the past two years VOA has begun a 82 billion broadcasting plant and operations modernization and expansion program and the consideration of appropriate R&D activities. Adequately staffed, funded, and administered, and carried out with imagination, determination, and political sensitivity, these efforts should provide an enhanced U.S. audio shortwave signal broadcasting capability the end of this decade. Indeed if all countries adopted some of the promising technological and operational methods and means that the VOA is now planning to study experimentally, the overall operating climate for HE audio broadcasting would be significantly improved. But even when VOA and RFE/RL meet their new goals, the serious inherent limitations in the surface-based HF ionospheric mode of shortwave broadcasting audio signals in real time over long distances will remain with them, and all other shortwave broadcasters. These limitations are so fundamental and so severe that, given any sensible alternative, the United States should not depend upon the current mode any longer than necessary. Indeed neither should any other country. In addition to acquiring the best possible HF shortwave capabilities, we should urge and assist other countries in working with us to pursue an acceptable and sensible alternative. The serious limitations of surface-based HF shortwave are generally well known throughout the community of broadcasters. Important limitations include i. Inherent complexity in identifying truly useful operating frequencies, and in reaching acceptable multicountry agreements to their specific allocation and proper use 2. Limits on the range of signal distance created by the geometry of the Earth's surface and its ionospheric layers When audiences to be served are located beyond the approximately 2,000-mile maximum one-hop signal distance from a shortwave transmitter, repeater transmitters must be located in other countries sufficiently close to the audiences. The use of remote transmitters involves important political, financial, and operational costs, including substantial payments to the host countries. There is also always the possibility that repeater r _ ~ _ WORKING PAPER
WORKING PAPER transmitters will not continue to be available in circumstances where their availability would be particularly valuable. 3. Potential interference by shortwave signals reflected and scattered by the ionosphere Shortwave signals broadcast to an audience area one hop away from a transmitter are reflected and scattered upward and outward from this surface area and are propagated back down toward the Earth via the ionosphere, perhaps several times. This phenomenon creates the potential for interference over great surface areas. Signals transmitted to serve listening areas two or more hops away may present potential interference to audiences in the intermediate hop area or areas. Signals radiated in directions other than the direction of the intended audience area (i.e., signals that are also always radiated from the broadcasting transmitter antenna's sidelobes and backlobes, even though of lesser intensity than those radiated from its main lobed also may cause interference to additional audiences distributed over great areas. Indeed HE shortwave transmitters and their antennas, the Earth's surface, and the ionosphere are dull and fuzzy tools for focusing audio broadcasting signals efficiently onto specific listening audiences. Poor, distorted, reduced, or lost signal Often the received signal quality is poor because natural variations in ionospheric radiowave propagation conditions cause rapid and intense variations or fading in received signal power. Multiple overlapping signals, arriving at the receiver may be delayed in time one from another because components of the originally transmitted signal have travelled along markedly different Earth-ionospheric paths. These signals often fade rapidly and are often distorted when they reach the listener. Intense electrical noise bursts generated during electrical storms or thunderstorms in the general vicinity of the receiver can also reduce listening quality or completely overcome reception of the desired signal. Loss of signals altogether can occur when the ionosphere is sufficiently disturbed. A powerful burst of solar energy, for example, can change the ionosphere's electrical characteristics suddenly and profoundly when that energy reaches and interacts with the ionosphere. Commercial-industrial noise Signal quality can be degraded by the electrical noise accompanying the expansion of commercial and industrial activities. 6. Interference by other signals Signal quality can be degraded by inadvertent interference by signals arriving simultaneously from other broadcasting 6 WORKI NG PAP ER
WORKING PAPER transmitters that utilize the same or nearly the same transmitted frequency. These interfering signals may be propagated directly or reflected via the ionosphere toward the receiver. 7. Jamming Signal quality can be degraded and useful signal reception can be prevented by jamming transmitters. Jamming affects the listeners the jammer focuses on and often also affects listeners in other countries who cannot escape the jammer's signals. 8. Changes in transmitter frequency Many listening audiences are required to readjust their receivers several times throughout the day, sometimes hour-to-hour or more often, to receive signals from a given broadcaster. These frequent changes are necessary as the broadcaster changes transmitter frequency to accommodate changing radiowave propagation conditions and/or unintentional and intentional interference. 9. Operating complexity and high cost The complexity and cost of the capita] and operations and maintenance (O&M) required to maintain an acceptable broadcasting service encompass increasing a broadcasting system's effective radiated power, the number of simultaneous transmissions on different radio frequencies, and extra-country repeater transmitter sites. These requirements continue in the face of a seemingly inexorable increase in signal interference as many countries adopt the same methods to retain or enhance their own competitive position as they cope with limited natural resources--in brief, the problem of the global commons. Similar concerns face the VOA and RFE/RL as they begin to plan for modernization and expansion of their broadcasting plants. Their concerns include the following: l. A sharp increase in the number of distant repeater sites located within other countries. 2. An increase in overall system effective radiated power at great capital (probably 62 billion) and ongoing O&M (probably 5300 million per year) cost. 3. Dependence upon the availability of many satisfactory frequencies. 4. Dependence upon an audience willing to track VOA and RFE/RL broadcasts by retuning receivers as broadcast frequencies change. The VOA and RFE/RL engineers now accept service limitations such as audience areas of secondary as well as primary service quality, and--even in 7 WORKING PAPER
WORKING PAPER the primary listening areas--being able to serve only 90 percent of the desired locations and for only 90 percent of the time. Even this level of service can be maintained only if the signals are degraded by no more than modest levels of manmade noise and unintentional interference. Such service levels are two orders of magnitude (expressed in powers of lO) poorer in quality and reliability than those delivered by U.S. commercial AM, FM, and TV over-the-air broadcasters. Although some of the lower-power local AM stations may be confronted with skywave propagated interference outside of their primary service areas, the latter two are generally interference free. Over the longer term, other countries will follow the same course to regain their broadcasting effectiveness and match increased U.S. effectiveness and this trend could neutralize the relative advantage the United States has purchased at such great cost. Perhaps the greatest longterm threat to the effectiveness of any surface-based shortwave audio broadcasting service is the gradual loss of audience share. Several factors make this threat a read possibility, including continued efforts by many countries to increase their use of great effective radiated power and multiple simultaneous frequency broadcasting, raising the general susceptibility of received signals to degradation. The proliferation of other electronic communications products such as audio and video tape players, recorder-players, and high quality stereo receivers, and radio and TV services also adds to the competition for today's HE shortwave listening audiences. The fundamental and grave deficiencies of this particular broadcasting mode place it at growing disadvantage when compared with other electrical communication modes available in a world of growing electronic communications and sophistication.3 Yet listening to audio broadcasting generally appeals to the general public if broadcast quality, reliability, price, and program content are acceptable, even when the broadcast competes with other activities. In the relatively financially and culturally rich and sophisticated area as Washington, D.C., with its diverse mix of over-the-air and cable television, newspapers, magazines, motion picture houses, orchestras, theatres, museums, sports activities, 23 over-the-air AM and FM broadcasting stations thrive. The United States has more than 9,000 local over-the-air AM and FM broadcasting stations. Ninety-nine percent of U.S. households have at least one radio; the average number per household is 5.5 sets. 3 . The VOA recogn i zes ~ he gravi ty of ~ hi s compet i ~ i on: " ~ VOA broadcast) ng ~ would have difficulty attracting significant audiences in countries that already have an abundance of sophisticated technologically advanced radio, television and print medi a tand] VOA sources. . . looking into the technical question of how to deliver the product tin Europe] say that ~already] the old short-wave transmissions can no longer attract listeners." {The Washinoton Post. June 13, 1985, page A-6.) WORKING PAPER
WORKING PAPER Fortunately, an audio broadcasting option should be available to the worldwide broadcasting community within the next decade that will offer all countries the prospect of obviating the deficiencies inherent in surface-based broadcasting. Transmitters placed in orbit high above the Earth could receive broadcasting programs directed toward them from the Earth and then rebroadcast the programs directly to audiences living in most areas of the world. These space rebroadcast transmitters would operate on fixed frequencies high enough to avoid all important ionospheric influences. They could deliver a broadcasting service with great surface coverage and high quality. And they could do so at the lowest per channel cost, with the greatest value to the world, if the broadcasting service were of large capacity and were offered in the common user-common carrier form. In recent years the executive branch of the U.S. Federal government has given growing attention to the practical possibility of-using space broadcasting to meet the needs of the VOA, RFE/RL, and the Armed Forces Radio Network. Congressional hearings have been held on the issue. NASA, working with the VOA, has conducted early, related systems studies and may conduct experiments in space. There is now a general hope, bordering on trust, that satellite communication will soon find its place in global broadcasting.- This paper outlines the fundamental technological and operational characteristics of two similar, direct audio satellite broadcast, very-high-capacity, common carrier-common user, system-services. Initial estimates are made of their acquisition and ongoing financial costs, and observations are made regarding how these costs could be met. Although many radiowave bands may be used for broadcasting and/or for space-related communications, at present there are no bands set aside by international agreement to be used specifically for broadcasting audio signals from space directly to individual, not community, surface receivers. To date discussions of ways to provide regional DBS-A system-services have focused upon two quite different portions of the electromagnetic spectrum. One band is in HE (25.67-26.10 MHz) and is already set aside for direct audio broadcasting but with no explicit recognition that broadcasting transmitters could be located in orbit above the Earth as well as on its surface. The other band is in UHF (2500-2690 MHz), where broadcasting from orbit for community reception at the surface would be allowed to take place, but where the power flux density at the surface is so limited as to discourage a broadcasting service that would allow reception by the general public. Such space broadcasting would have 4. "Through the explosion of satellite communications, a technological 'genie' has been unleashed which will change forever the way that governments communicate ideas and information abroad," Charles Z. Wick, director of the United States Information Agency, in a speech delivered at the George Washington University, Washington, D.C., May 5, 1985. _ 9 _ WORKING PAPER
WORKING PAPER to be shared with fixed- and mobile-surface services.5 This paper's exploration of the two conceptual DBS-A system-services assumes that appropriate frequency allocations could be made in either of the HE or UHF bands and compares their general characteristics. This paper does not explore the intriguing possibility of employing very-high-altitude powered platforms tHAPP's) now under study by the Department of Energy and NASA. These platforms are to be crewless, lighter- or heavier-than-air craft that could be kept high in the air but not in orbit at altitudes of lO to 20 miles (16 to 32 kilometers), hovering over a selected surface area for a year or more or forever. They would receive power to drive their electric engines and support their payloads via a collimated microwave beam of electrical energy directed upward to them from the Earth. Powerful HE band signals could be broadcast directly from such platforms. If a HAPP were stationed at an altitude of 20 miles, the signals broadcast from it could be received at distances of as much as 400 miles (620 kilometers). The signals would avoid most ionospheric influences and, therefore, would deliver reliable, steady, and clear audio programs. They could be used in some circumstances to complement the worldwide, space-related, system-service outlined here. 5. Footnotes 757 and 2561, ITU Radio Regulations lO WORKING PAPER
