Antennas, Satellite Broadcasting, and Emergency Preparedness for the Voice of America (1988)

This chapter presents the Voice of America (VOA) with a roadmap for introducing satellite audio broadcasting technology, and the improved services which it allows, into its operations to compensate for many of the transmission and reception limitations of its terrestrial, high-frequency (HF), relay network.

The related question of television broadcasting must receive only passing mention at this point, although that medium is an increasingly effective one. There might be merit in assessing the relative emphasis on the two media, but that assessment lies outside the scope of this report for the following reasons. First, the VOA has elected to pursue its informational programs through the audio medium and has not formulated a role for itself in television. Secondly, the Television and Film Service of the United States Information Agency (USIA) is responsible for use of the television medium in the USIA mission. Therefore, analysis of the value of television broadcasting and the various technical opportunities for implementing it would be more properly addressed to units of USIA other than VOA.

The topical sections that follow correspond closely to items described in the Statement of Task. A phased introduction of direct audio broadcasting by satellite (DBS-A) is shown to be technologically, economically, and politically feasible, within certain limits that the VOA should recognize in its planning for use of this transmission system. Even though a new generation of receivers for satellite reception is required, they can be produced on a short lead time, and this new transmission system can eventually complement the ongoing modernization of the terrestrial HF facilities. The long-term goal to be addressed is the provision of a global service that offers the promises of international political acceptability, lower cost per channel, excellent reliability and quality, and less vulnerability to interference.

The development of DBS-A is not merely a question of exploiting technological possibility. HF is currently an accepted form of international broadcasting, with a long history of development and use.

Introduction of a new satellite service by one or more major international broadcaster(s) will require not only that satellites be put into orbit and receivers designed, manufactured, and marketed, but also that parallel strategies be developed to overcome economic and political obstacles to effective deployment of the system.

On the economic side, the development of DBS-A must contend with problems of international debt, trade restrictions, and manufacturer attitudes, which could delay introduction of receivers or keep their prices artificially high for an extended length of time. Deployment of DBS-A as a system directed primarily at developing countries, for instance, must contend with the attitude among Asian manufacturers that their profitability is best assured by concentrating on markets with high income elasticity of demand, which is not the case outside a few countries of the industrial West, Japan, the Pacific rim, and Australia and New Zealand.

On the political front, achieving a dedicated DBS-A band allocation for regional and international broadcasting must be made a priority of U.S. delegations to the upcoming Orbit World Administrative Radio Conference (Orbit-WARC). This is essential to gain the cooperation of other countries to accept DBS-A signals into their territories, as they could broadcast their DBS-A programs in turn to yet other countries. This could best be done by pursuing the “common carrier” approach to using satellites, or by some variation of this approach, such as providing broadcast time on transponder capacity leased to the VOA for domestic or regional services. The attitude of the Soviet Union is perhaps most crucial, since the VOA has major audiences there and should continue to develop such audiences. But the opposition of the Soviet government to such a broadcasting system would slow the ability of its people significantly to acquire the necessary technology to receive such signals. Pursuing the opportunities provided by glasnost would seem to be in order. In any event, the VOA could use a space-based broadcasting service to reach most of the audiences of the world while continuing to use HF, as it does today, to reach those remaining, non-cooperative ones.

Finally, the VOA should recognize, and adopt policies to address, the fact that both economic and political difficulties for this new system could be ameliorated by its own programming changes. People will seek ways to overcome obstacles to access to technology if they have an incentive to do so. As countries’ domestic services move toward higher-fidelity, very-high frequency (VHF) terrestrial systems and people invest in such technologies as audio-cassette players, portable personal radios, compact-disk players, and video-cassette recorders, their expectations of broadcast signal quality and reliability will increase. This seems to require that the VOA consider supplementing HF with other transmission systems, and DBS-A is an obvious choice. But merely providing news programming already available through other channels may not provide the incentive required for people to invest in the necessary reception technology. The programming must exploit the fidelity potential of the technology and compete well against the other options available. Otherwise, investment in such a system would be a waste of resources.

For DBS-A to succeed, then, the context for its development must be

seriously considered. This context requires that the VOA undertake planning not only on the technological questions of transmission but also on effective means to overcome economic and political obstacles and on programming developments that can create the demand necessary to spur production, purchase, and use of the required receivers.

The recent study for the USIA by the Academy for Educational Development (Fortner, et al., 1986) addressed technological, economic, and political issues affecting radio receiver populations in various parts of the world, with projections through the turn of the century. In detailed and quantitative terms, the report showed that present receiver populations are very unevenly distributed around the globe because of different economic conditions and national, political regulation. Technically, the receiver characteristics in various regions depend directly on the types of signals locally available, medium wave (MW) and short wave (SW) being dominant, with a much lower quantity of VHF units. With no microwave signals (at the frequencies from 1 to 12 GHz that are efficient for DBS-A purposes) currently available, there are, of course, no microwave receivers. Such receivers are not currently produced because there is no consumer demand, and there is no demand because there are no satellite transmitters delivering quality programming. However, several manufacturers have observed that appropriate receivers could be delivered within only six months of a perceived demand. Thus, the introduction of DBS-A need not be hamstrung by unrealistic requirements that its transmissions be compatible with the existing medium-wave and short-wave receivers, although some countries, where the governments control their publics’ access to international broadcasting receivers, are special cases. The history of frequency-modulation (FM) radio and color television outside the developing world has shown that, when new classes of signals with desired program content are made available, user demand and receiver production expand rapidly to exploit the additional benefits of the new medium.

Two possible strategies for the VOA to follow as part of an overall plan for development of DBS-A in spurring development and marketing of inexpensive converters or receivers are (1) to publicize its interest widely in development of prototypes that could then be copied by ^“low-end^” manufacturers and (2) to spur development of such devices by placing an order itself—say, 10,000 to 100,000 units—which could be distributed initially to “prime” the market. These receivers could be used provided that some satellite audio broadcast services were made available in an introductory or auxiliary way, using existing satellites. If such receivers were to cost, say, $300 per unit, comparable to costs estimated by the Communications Satellite Corporation for its DBS-TV receivers, an initial market-priming order of 10,000 would cost $3 million. It could well result in establishing a viable manufacturing business in the U.S. economy in addition to opening the way for DBS-A services for the VOA.

Rogers (1985, 1987) noted that the limitations of surface-based, HF (short-wave) transmissions are generally well known throughout the community of international, long-distance, audio broadcasters. The following is a partial list of these limitations:

1. Complexity in selecting useful operating frequencies and in reaching international agreements for their specific allocation and use

2. Distance constraints between transmitting and receiving areas because of the geometry of the Earth’s surface and its surrounding ionospheric layers

3. Interference from other short-wave signals, broadcast on the same or nearby frequencies, that are also reflected and scattered by the Earth’s surface and the ionosphere

4. Fading, distortion, and loss of the received signal because of variations in the altitude and charge density of the ionosphere brought about by solar-diurnal, seasonal, storm, and sunspot-cycle effects

5. Interference from commercial and industrial noise emanating from the machinery of expanding industrialization in the receiving areas

6. Intentional interference, i.e., “jamming” from unfriendly transmitters whose intent is deliberately to prevent reception of these signals in particular areas

7. Changes in the transmitter frequency and corresponding, required retuning of the receiver by the listening audience throughout the day, to offset the variations in ionospheric reflection or to counteract jamming

8. Technical complexity and high costs, both for initial acquisition and installation and for continuing operation and maintenance, of the many high-power transmitting stations distributed around the world to achieve the desired audience coverage

9. The utility of overseas repeater sites dependent upon the stability of agreements between the United States and host countries.

For the VOA in particular, these general limitations of long-distance, HF broadcasting have several impacts on its modernization program. To increase audience coverage and improve probability of satisfactory reception, additional distant repeater sites located within foreign countries and operating with high-power transmitters are being constructed. The effectiveness of these stations depends upon the availability of many frequencies and upon audience willingness to retune to track VOA broadcasts. Even so, the VOA must accept significant degradations in service quality, reliability, and availability compared to commercial, over-the-air, AM and FM service in the United States.

In contrast, a DBS-A service promises widespread and predictable surface-area (audience) coverage and excellent reliability and quality of reception. Offered as a large-capacity, common-carrier, common-user service it should find general acceptance among the countries of the world; also, it would confront any potential jammer with severe political repercussions. With little DBS-A experience to date, this technology’s

relative effectiveness with respect to terrestrial HF broadcasting is subject to some debate. However, the relevant physical laws for radio-wave propagation, transmitter power, antenna gain, receiver sensitivity, and signal quality are well known; furthermore, there is extensive satellite communications experience at many frequencies from both low- and high-altitude orbits to guide the choice of system parameters for DBS-A service. This experience, together with the current state of space technology, provides a sound basis, both technically and economically, for the phased introduction of DBS-A, initially as a supplement and ultimately (i.e., over the next decade or later) as a replacement for the majority of long-distance, terrestrial HF, broadcasting transmitters.

Numerous studies (Bachtell et al., 1985; Horstein, 1985; National Research Council, 1986) have shown that satellite broadcasting in the HF band to achieve compatibility with the existing, short-wave, receiver population would require satellite power levels and antenna diameters that are beyond the current state of the art, as illustrated in Figure 3–1. Similarly, at or near the FM band, 88 to 108 MHz, where millions of receivers already exist, space-segment antennas of the directivity required for regional coverage need apertures beyond the state of the art for space structures. In addition, the required power density incident on earth would create unacceptable interference with the reuse of certain terrestrial FM and television frequencies and therefore contravene the Radio Regulations of the International Telecommunication Union (ITU). However, satellite system configurations become feasible for audio broadcasting channels at microwave frequencies above 1 GHz. Correspondingly, 2.5 GHz and 12 GHz bands have already been designated by the ITU for satellite broadcasting. At microwave frequencies, the characteristics of the transmission path from space to a receiver at or near the Earth’s surface are entirely determinate (although attenuation through foliage and building walls may have to be included as explained below). This advantage stands in contrast to the fading and interference of terrestrial, HF signals caused by the vagaries of the ionosphere. The only significant variable in the satellite-to-earth transmission path is a frequency-dependent attenuation through foliage, building walls, and heavy precipitation, varying from nearly negligible at the end of the ultra-high frequency band (UHF) to high (10 to 20 dB) at 12 GHz. In general, a statistical base must be established to account for such excess attenuation values—values which can be expected to vary with receiver location (e.g., inside or outside of buildings, in desert or tropical regions), season, and climate. The straight-path loss from the satellite to all receivers within the line of sight limited by the Earth’s curvature and rough terrain is virtually constant, unlike the varying reflections of HF waves from an ionosphere whose properties change diurnally and seasonally and which can be seriously disrupted by solar storms. Therefore, a single, fixed frequency can provide continuous service to a given area, freeing the listener from retuning.

The service area available for satellite broadcasting is a function of satellite altitude, orbit inclination, and antenna beamwidth. Studies of low- vs. high-altitude orbits (Bachtell et al., 1985; Horstein, 1985) illustrate that two of these orbit classes are the most attractive for

practical communications from satellites because of their long (or continuous) visibility to the service area: the geostationary orbit and the so-called Molniya orbit. The Molniya orbit has been employed extensively by the Soviet Union because of its northern latitude coverage. The geostationary orbit has been found more advantageous in the Western world, including northern Canada and Alaska, because of its freedom from satellite tracking requirements by the earth stations. Lower orbits, such as the eight-hour, near-equatorial, and sun-synchronous orbits studied in these references, have the appeal of lower cost per pound of communications payload into orbit, but their short time in view and multiple frequency demands limit their utility for broadcast service. (The Committee understands that the VOA has further study of particular, eight-hour orbits under way but has not yet reviewed that work.) Accepting the higher cost of launching hardware to geostationary orbit and the greater demand on satellite effective antenna gain, the primary limitation of such orbits is the geometrical constraint in northern- and southern-latitude coverage. This latitude constraint is not significant for the VOA since all 15 of its service areas lie within ±70 degrees of latitude, which is within view of appropriately located geostationary satellite(s).

Use of microwave frequencies for satellite broadcasting offers a degree of immunity from intentional interference, i.e., surface jamming. Line-of-sight properties of microwave propagation restrict the influence of interfering transmitters with a 1,000-foot antenna height to a radius of 40 to 50 miles, so that prevention of broadcast reception over large areas involves great cost. It is unlikely that jamming of the satellite uplink would be attempted because the uplink’s characteristics could be designed to be jam resistant. Antijam techniques already used on military satellites employ uplink receiving antennas of high directivity, spread-spectrum modulation, and multiple linear receivers. Furthermore, mutual self interest encourages international compliance with ITU conventions in the use of a large-capacity, common-carrier, common-user system.

At this time, before any DBS-A system has been defined or procured, the accuracy of cost comparisons between terrestrial HF and satellite broadcasting operations is perforce limited. However, the relative magnitudes can be estimated based on the known history and projections of the VOA and the histories of satellite communications systems already in use for domestic and international fixed service. Table 3–1 summarizes the capitalization and operating costs of one VOA relay site, one international satellite, and one domestic satellite over a ten-year period. Figures in the terrestrial HF column are based on the current VOA modernization program, ranging from $100 million to $150 million per site for local government fees, civil works architecture and engineering (A&E), and equipment added to the current operations and maintenance budget of $70 million per year, which covers the operation of the equivalent of

8 1/2 relay sites. Each site contains several transmitters and antennas. Figures for the two satellite columns in the table are based on actual, commercial experiences of international and domestic owners and operators.

This gross comparison illustrates that the annualized cost of one terrestrial, HF relay station is approximately equal to that of one satellite, taking into account their respective equipment lifetimes of 20 and 10 years. It is, of course, significant that a typical VOA relay site can transmit only on the order of five to eight signals simultaneously, all with the geographical and time-dependent coverage limitations discussed above. By contrast, a satellite can transmit hundreds of audio signals simultaneously, depending on its design, with no time constraints and potential coverage of 90 to 120 degrees of longitude and ±70 degrees of latitude. Thus for total VOA coverage comparisons, there would be a large, per-channel cost difference in favor of four geostationary satellites over a total of 10 to 15 terrestrial HF sites. Also, the useful lifetimes of in-orbit satellites continue to grow.

Studies over the past several years have addressed the future implications of large space platforms, both in geostationary orbit (Edelson et al., 1987; Barberis and Brown, 1986) and with the planned Space Station in low orbit (Vinopal and Willenberg, 1984). Because of its brief time in view, from any location on the Earth’s surface, the Space Station is considered as either an experimental facility or a staging base for in-orbit assembly of large space structures rather than an operational platform itself for large-antenna, high-power, communications systems. The potential availability of such large-antenna, high-power platforms was the impetus for some of the HF systems described in the National Aeronautics and Space Administration (NASA) studies for VOA (Bachtell et al., 1985; Horstein, 1985). As emphasized by Rogers (1985, 1987) and the National Research Council (1986) the time scale for developing and demonstrating the technology for very large geostationary satellites is greater than 10 years. Neither antennas in the range of 100 m diameter nor power systems in the range of hundreds of kilowatts are likely to be available in space for the next several decades within the current and planned programs for large space station development and deployment. The recent schedule stretchout for the Space Station deployment following the loss of the Challenger probably will delay their availability further.

The above considerations argue strongly that large geostationary platform technology will not affect DBS-A in the near term. For their own agency interests, the Directors of the VOA and USIA should inform the Administrator of the National Aeronautics and Space Administration that it would be in the interests of the VOA and USIA (and, presumably, in the interests of the United States space and communications industries) if NASA were to proceed with the development of fundamental space technology needed to engineer effective and economical DBS-A systems.

Meanwhile, present communications satellites could be employed initially, with special earth receivers used to allow local rebroadcast of the received signals. Then, perhaps, the technologies now being applied to DBS-TV could be adapted for DBS-A, with initial introduction by means

of add-on payloads as described in the later section, Augmentation of Terrestrial High Frequency. Finally, a true, large-capacity, DBS-A system and service could be introduced.

Before speculating on the future applications of DBS-A by third-world nations, it is well to note that two satellites owned and operated by two third-world countries for the purpose of direct satellite broadcasting, both television and audio, are already in geostationary orbit. The multimission INSAT located at 95.3 degrees East longitude contains payloads for fixed-service communications at 4 and 6 GHz, broadcast service at 2.5 to 2.69 GHz, and meteorological remote sensing. Two Arabsats, located at 19 and 26 degrees east longitude, serving the seven nations of the Arabian Satellite Organization, are also multimission satellites with twelve fixed-satellite channels at C-band (4 and 6 GHz) and two DBS channels at 2.5 GHz. Those satellites are still young in their respective lifetimes, so the extent of DBS service and the number of receivers are constrained by their current experimental nature. As the technology, service, quality, and receiver affordability are demonstrated over the next several years, DBS-A will become attractive to other third-world countries that can neither afford their own satellites nor have the abundance of terrestrial broadcasting services available in the West and in Japan.

Broadcast satellites are being vigorously developed by Japan, Europe and Australia, primarily for television. The feasibility and desirability of incorporating DBS-A into these television broadcast satellites are recognized, and plans are in place to utilize them accordingly (Miller, 1987; Treytl, 1987; Johnson, 1987). By contrast, the United States has no current DBS program commitment to such an international activity in broadcasting satellite development, deployment, and use. The VOA, NASA, and the broadcast industry have not yet coordinated nor focused their efforts to apply available technology to provide DBS-A.

While not strictly a satellite broadcasting service in the sense of direct user reception, radio programs are regularly distributed by satellite communications circuits in the United States, for example, by public radio, to affiliated amplitude modulation (AM) and FM stations. Equatorial Communications employs spread-spectrum techniques to broadcast Muzak service directly to franchised users with small-antenna terminals (2 to 3 feet at C-band, 4 GHz).

The predecessor committee’s report (National Research Council, 1986) clearly recognized that replacement of the VOA’s HF, terrestrial, broadcast facilities with direct-broadcast satellites transmitting at HF is neither technically nor economically feasible for the very near future. However, the state of the art of satellite technology does offer several options for introductory use of satellite transmitters by the VOA and others for limited broadcasting or auxiliary functions. In each case,

the following excerpts from the cited report recommend the early use of satellite transmitters to augment, not to replace, terrestrial HF:

• “…DBS-A initially to supplement the present VOA worldwide system.” (page 4)

• “…explore the possibility of providing low-capacity, direct audio broadcast satellite services at a relatively early time.” (page 12)

• “…added to one or more private communication satellites to make VOA programming available at very low cost and with high quality and reliability.” (page 13)

• “The VOA should plan for phased introduction of satellite services:

  • Near-term experimental phase

  • Relay of VOA terrestrial transmissions

  • Possible first-generation system based on current technology

  • Possible second generation: higher capacity and worldwide” (page 58)

• “Satellite augmentation of terrestrial facilities:

  • Provision of additional services at S-band

  • Closed-loop monitoring of HF transmissions

  • Jamming avoidance” (pages 71–72)

• “Local distribution of programming material” (page 72).

All these current technology options for supplementing terrestrial HF broadcasting with DBS-A, whether by joint demonstration experiments (e.g., with INSAT, as recommended in the predecessor committee’s report) or by add-on payloads, would employ frequencies authorized for satellite broadcasting in the UHF or super-high frequency (SHF) bands rather than at HF, for the reasons discussed in the earlier section, Effectiveness of High Frequency vs Direct Broadcast Satellite. Although receivers for these bands are not now available in quantity or at reasonable cost, the survey cited in the earlier section, Receiver Availability, showed that this lack is not due to technical factors but to lack of demand. Demand will motivate manufacturers readily when signals are available for reception. As noted in the survey, the manufacturers^’ response time is measured in months, not years, and this is considerably shorter than the several years^’ development and deployment cycle of the satellite equipment.

The potential advantages to the VOA (and to all the other international, audio broadcasters throughout the world) of DBS-A in terms of reliability, service-area coverage, signal quality, reduction of installation and operating costs, channel capacity, and reduction of the likelihood of jamming are compelling. Over a year has passed since the findings and recommendations of our predecessor committee urged the VOA to establish within its organization a group responsible for formulating and

implementing a plan to introduce satellite broadcasting into its operations. Four elements of such a plan were defined for this new element of the VOA organization (National Research Council, 1986):

• Long-range planning and development program

• Study of 2.5 to 2.69 GHz DBS-A

• Phased introduction of a worldwide, direct-satellite-broadcasting service (near-term experiments and demonstrations, satellite relay of terrestrial programming, first and second generation systems and service, and receiver development at appropriate frequencies)

• Political, financial, and regulatory matters fundamental to worldwide acceptance of DBS-A.

Indeed, the report states (at p. 11), “Direct audio broadcasting by satellite…could be available by the year 2000,” and “An institutional arrangement should be considered…for the possible provision of a common-carrier, common-user service.” As yet, there is no formal, organizational focus within the USIA or VOA to address DBS-A.

These recommendations are still valid. The Committee reiterates them as all the more urgent as they have to be incorporated into the VOA’s activities in time to allow the United States to be prepared satisfactorily for the 1988 World Administrative Radio Conference.

The VOA should now begin to position itself to enter the age in which satellites are used to supplement terrestrial, short-wave transmitters so as to improve direct-to-the-listener broadcasting of its programs. Technologically, the way is now clear for orbiting transmitters to broadcast audio programs directly to home receivers over nearly the entire globe (and in particular to all 15 of the VOA service areas), to do so with the excellent quality and reliability offered by satellite communications circuits today in the provision of radio and television distribution services and to do so at a lower unit cost than that of surface-based HF. The following four recommendations constitute the major milestones in a roadmap for the VOA’s introduction of satellite direct audio broadcasting. The Director of the VOA should take the following actions:

1. Assign a senior professional with ready access to the Director (perhaps in a new position of Chief Scientist) the responsibility and staff (of not more than two or three people) to develop the details of a phased plan for:

   1. Demonstrations with existing satellites

   2. Subsequent provision of early, modest, DBS-A capability via add-on payloads to host satellites

   3. The definition of a dedicated, high-capacity, common-carrier, world-wide, satellite DBS-A system.

2. Allocate a modest sum, say $500,000 annually, for this designated professional to engage the services of satellite technology and service experts to assist in defining such a multiyear VOA plan.

3. Participate actively, with VOA in-house and contractor support personnel, in developing the U.S. delegation position in concert with the National Aeronautics and Space Administration and the Departments of Commerce and State for the forthcoming 1988 Space World Administrative Radio Conference concerning allocation of frequencies for direct satellite broadcasting of audio programming, and participate in the delegation’s activities at the Conference.

4. Engage in liaison with the receiver industry, both domestic and foreign, to define the characteristics and economics of a new generation of DBS-A receivers, enlisting industry participation in the initial demonstrations noted above.

5. The Directors of the VOA and USIA should inform the Administrator of the National Aeronautics and Space Administration that it would be in the interests of the VOA and USIA (and, presumably, in the interests of the United States space and communications industries) if NASA were to proceed with the development of fundamental space technology needed to engineer effective and economical DBS-A systems.

In addition to these recommendations for USIA or VOA action, the concept of DBS-A is now sufficiently mature technically, financially, politically, and operationally for the Committee to recommend that VOA inform both the White House and the Congress of the opportunities that it presents.

Bachtell, E.E., S.S.Bettadapur, J.U.Coyner, and C.E.Farrel. 1985. Satellite Voice Broadcast System Study. Final report by Martin Marietta Corporation to the NASA Lewis Research Center. NASA-CR-175017. Cleveland: National Aeronautics and Space Administration.

Barberis, N.J. and J.V.Brown. 1986. Design Summary of a Geostationary Utilized as a Communications Platform. Paper presented at American Institute of Aeronautics and Astronuatics (AIAA) 11th Communication Satellite Systems Conference, March 17, 1986. AIAA Paper No. 86–0714.

Edelson, B.I., R.R.Lovell, and C.L.Cuccia. 1987. The evolution of the geostationary platform concept. IEEE Journal on Selected Areas in Communications. Vol. SAC-5, No. 4, May.

Fortner, Robert S., et al. 1986. A Worldwide Radio Receiver Population Analysis. Washington: The Academy for Educational Development. May.

Horstein, M. 1985. Satellite Voice Broadcast System Study. Final report by TRW, Incorporated to the NASA Lewis Research Center. NASA-CR-174905. Cleveland: National Aeronautics and Space Administration.

Johnson, C. 1987. DBS Systems Including Sound Broadcasting. Paper presented at the 15th International Television Symposium, Montreux, Switzerland . June 12, 1987.

Miller, J.E. 1987. Technical Possibilities of DBS Radio at Near 1 GHz. Paper presented at the 15th International Television Symposium, Montreux, Switzerland. June 12, 1987.

National Research Council. 1986. Modern Audio Broadcasting Facilities for the Voice of America. Washington: National Academy Press.

Rogers, T.F. 1985. Spaced-Based Broadcasting: The Future of Worldwide Audio Broadcasting. Washington: National Academy Press.

Rogers, T.F. 1987. Worldwide direct audio broadcasting from space— promoting “glasnost” with DBA-A. Space Policy 3(August):232–238.

Treytl, P. 1987. Demonstrations of 16-Channel Sound Broadcasting by DBS. Paper presented at the 15th International Television Symposium, Montreux, Switzerland. June 12, 1987.

Vinopal, T. and H.Willenberg. 1984. Space Station Impact on Communication Satellite Systems. Paper presented at American Institute of Aeronautics and Astronautics (AIAA) 10th Communications Satellite Systems Conference, March 21. AIAA Paper No. 84–0705.