Showing papers in "IEEE Transactions on Broadcasting in 1988"

Planar antennas for satellite reception

Abstract: Direct broadcast satellite (DBS) reception requires a circularly polarized antenna with high gain and low axial ratio. Recently, various types of planar antennas have been studied and developed for DBS reception in the 12-GHz band. A summary is presented of properties and classification of planar antennas both commercialized and reported. The basic configurations, working principles, and performance of various planar antennas are described. >

Collocation of receivers and high-power broadcast transmitters

Abstract: Receiving antennas and receivers can be collocated with the transmitting antennas and transmitters, if appropriate interference suppression is effected. Since the time-varying characteristics of the interference from adjacent transmitters may not be known a priori, and since the propagation path characteristics may change with time, interference needs to be suppressed by adaptive means. Operational characteristics of the adaptive control system in a shortwave broadcast station and expected degree of cancellation of the unwanted interference are discussed. Some recent tests to evaluate the effectiveness of the adaptive control in the relay station of Voice of America at Delano, California are outlined. Both laboratory and field tests show that adaptive interference-suppression systems can be designed and built for real-life environments expected in broadcast and relay stations. >

Satellite broadcasting in Australia

Abstract: The operational features of the Australian domestic satellite system, AUSSAT, are discussed, particularly as they relate to broadcasting direct to communities and distribution to transmitters and studio centres of the Australian Broadcasting Corporation, ABC (Aus). Distribution of sound-only broadcasting programs is covered by the use of time-multiplexing using B-MAC. Comprehensive direct broadcasting from satellites is now available to many people living in remote areas of Australia who would otherwise receive minimal service. Initially, for each of the four major regions, ABC (Aus) has provided one television channel with stereophonic sound capability together with three different sound-only services, one of which is stereophonic. In addition to the 'free' services of ABC (Aus), commercial broadcasting satellite services are being progressively introduced to the four regions. >

Shortwave broadcasting band spectrum occupancy and signal levels in the continental United States and Western Europe

Abstract: The initial results are described for monitoring using a mobile spectrum monitoring unit (MSMU) that has the capability of fast sampling of radio signals in the frequency spectrum between 2 MHz and 1 GHz. In the summer and autumn of 1987, the MSMU was used to measure signal level and spectrum occupancy in the shortwave band (2-30 MHz) at four locations in the continental United States (CONUS) (i.e. Stanford, California; Ft. Huachuca, Arizona; Ft. Sill, Oklahoma; and Annapolis, Maryland) and at two locations in Europe (Seckenheim and Geinsheim, Federal Republic of Germany). After the measurement period, the recorded data was used to compute occupancy statistics at 111 signal amplitude thresholds. Comparison of spectrum-occupancy and signal-level data between CONUS and Europe is reported. >

High frequency propagation losses on an open wire transmission line above dissipative Earth

Abstract: Both exact and simplified approximate equations for the current on a pair of conductors above a dissipative Earth are developed. Since, in many practical cases, each conductor consists of a pair of wires, a method for reducing four-wire lines to equivalent two-wire lines is presented. The assumptions used in the approximate expression are that the cross-sectional dimensions of the line (e.g. the distances between conductors but not the height of the conductors above earth) are small compared to the wavelength, that the propagation constant in the Earth is larger than the one in air, and that the conductors are thin compared to the wavelength and any cross-sectional dimension. The first assumption restricts the validity of the equations for the current to below 100 MHz ( lambda =3 m) for typical transmission lines and the second assumption can be met for most practical air-Earth problems. Numerical results for transmission line loss are computed using both the approximate method and the exact method. It is seen that the two results agree well for frequencies less that 100 MHz. The loss is divided into conductor loss and Earth loss and plotted, and physical interpretation of the frequency dependence of each component is given. The results of a parametric study of transmission-line loss are given along with an interpretation. >

Novel dielectric-waveguide components

Abstract: A variety of resonators and bandpass, notch, lowpass, and highpass filters are described that use dielectric materials of high permittivity and are based on conventional waveguide technology. The devices are reasonably small, of high Q, and low loss tangent (tan delta ). The various configurations presented include the use of posts, inductive strips, waveguide resonator-filters, and re-entrant resonators. Also examined is the transition from a dielectric waveguide to a microstrip line. >

Comparisons and improvements of designs of data slicers and clock synchronization circuits for broadcast teletext decoders operating in a multipath environment

Abstract: It is shown that multipath propagation imposes a serious performance degradation on broadcast teletext systems designed according to the North American Basic Teletext Specifications. By using both analysis and a comprehensive computer simulation model of the teletext broadcast system, it was found that very significant gains in performance could be obtained by improving slicing level and clock synchronization circuit designs. Several slicing level and clock synchronization (also called bit timing recovery (BTR)) circuits were modeled and simulated and their performances compared. These included peak detecting, averaging, modified averaging, adaptive and ideal slicers. The averaging and adaptive slicers used with the correlator BTR circuit were found to give the best performance, but the complexity and cost of an adaptive slicer reduce the advantages of system implementation. >

RELEDOP: a full-scale antenna pattern measurement system for high-powered HF transmitting antennas

Abstract: A system is presented that utilizes a towed, 3-axis receiver called RELEDOP. RELEDOP is a receiving elementary dipole with optional polarization that measures the transmit directivity patterns of over-the-horizon backscatter (OTH-B) radars and shortwave broadcast transmitting arrays. A dielectric tow cable and a fiber-optic link to the towing aircraft permit excellent electromagnetic isolation of the RELEDOP sensor from the aircraft. High accuracy in position location (+or-15 m in x, y, and z) and fast-receiver sampling permit orthogonal polarization component measurements with accuracies of +or-0.15 degrees in bearing and +or-1 dB in relative amplitude. Calibrated receiving element gains permit measurement of absolute field strength. The field strength data, combined with the position data, permit an assessment of transmitter effective radiated power (ERP); a knowledge of input power permits a computation of absolute gain of the transmitting antenna to +or-3 dB or better. The RELEDOP system is described, along with its subsystems; towed sensor, airborne, positioning, ground station, and communications subsystems. Example patterns and flight path tracks illustrate the output graphics. >

High definition and high frame rate compatible NTSC broadcast television system

Abstract: The author proposes a method for terrestrial broadcast and cable transmission of high-definition television with high frame rate in the basic NTSC format using a single 6-MHz channel. The transmitted signal is appropriate for display on present NTSC receivers and generates a wide-screen display on new high-definition receivers with 1500 pixels horizontally on each of 966 lines in a 16:9 or 5:3 aspect ratio format. The author describes a method for motion compensation with receiver verification of motion vector data for the high-resolution monochrome portion of the signal, a method for video data by compression and quadrature modulation of the visual RF carrier. The overall hardware system has not yet been produced as hardware, but some of its components have been built in either hardware or software. >

Modelling a standard broadcast directional array with the numerical electromagnetics code

Abstract: The numerical electromagnetics code (NEC) is a general-purpose wire-antenna-analysis computer program capable of modelling both a standard-broadcast directional array (DA) and a scatterer such as a power line. The starting point for such a study is a NEC model of the directional array itself. The DA's admittance matrix could be used to choose voltage excitations for the NEC model such that NEC's tower-base currents agree in magnitude and phase with those of the array's design. However, this choice of excitation is unsatisfactory because NEC's azimuth pattern differs from the theoretical azimuth pattern which is computed using sinusoidal current distributions on the DA towers. The difference is accounted for by the phase of the tower currents: in the NEC model the phase varies with height above the ground on each tower, but in the sinusoidal current approximation, the phase of the tower current is constant. In the present study the NEC model of the DA is regarded as being out of adjustment, and the objective is to adjust the excitation of the NEC model such that its azimuth pattern matches the array's theoretical pattern. >

AM broadcast antennas with elevated radial ground systems

Abstract: Results are presented of computer modeling studies indicating that an elevated vertical monopole antenna with four elevated horizontal radials produces more ground-wave field strength than does a conventional ground-mounted monopole with 120 buried radials. For the analysis, the length of the radials and the height of the monopole were set equal to 0.25 of the free-space wavelength, and the frequency of operation was fixed at 1.0 MHz. Three different sets of ground constants were used, simulating averaging, very good, and very bad soil electrical parameters in accordance with the Numerical Electrical Code (NEC-GS). >

Ground loss effects in power line reradiation at standard broadcast frequencies

Abstract: Reradiation of a standard broadcast antenna's signal from a high-voltage power line is often analyzed by computer modeling. The resonant behavior of a power line operating over lossy ground is investigated using the numerical electromagnetics code (NEC) which uses the Sommerfeld-Norton (SN) ground model, for a highly accurate computation of the interaction of a power line with lossy ground. It is shown that lossy ground damps the resonant response of the power line and so, substantially reduces the reradiated field. Since the SN ground option is costly in CPU time, the effects of lossy ground were approximated using the tower footing impedance concept. A systematic evaluation of the accuracy of the approximation is made. An approximate technique for incorporating the approximate techniques presented are sufficiently accurate that the economical method-of-images solution can be used in most cases. >

The merits of modern technology for today's high power short-wave transmitters

Abstract: Developments in high-power shortwave transmitters are described, and practical experience with such transmitters is reported. Topics discussed are: high-level anode modulation, the pulse step modulator (PSM), the switching module, control of the PSM, the RF driver and final stage, and other modulation techniques. >

The future of high frequency broadcasting

Abstract: Since the end of World War II, the number of daily frequency hours used by high-frequency (HF) broadcasting (also known as shortwave and band 7, 3-30 MHz) has tripled. Approximately 35000 daily frequency hours are carried in an HF spectrum that can barely accommodate half that amount. As a consequence, congestion is severe, and interference levels intolerably high. Attempts to remedy this situation by planning the high-frequency bands date back to 1947, but, thus far, they have not been successful. International planning conferences in 1984 and 1987 have shown a possibility for agreement; another conference is tentatively scheduled for 1992. Some broadcasters have attempted to solve their congestion problems by moving out-of-band, sometimes expanding their services int bands allocated to other services, such as amateur radio, fixed, aeronautical, and mobile. It is feared this trend will continue. The attempts that have been made to plan the HF bands in an effort to alleviate congestion are described and the outlook for the remainder of the 20th century is discussed. >

A new design for high performance HF curtain antennas

Abstract: A method of optimizing high-performance high-frequency (HF) curtain antennas is presented. This optimization is based mainly on two criteria: global matching conditions at the transmitter output, i.e. the VSWR (voltage standing-wave ratio) at the input of the antenna, thus ensuring that the antenna is a correct termination to the transmitter; and, network dimensioning, expressed by the product P*S, whereby P=power in a specific radiator, S VSWR in the line feeding this radiator. This second point defines the correct distribution of power between the dipoles. Both criteria are defined by the antenna designer, mainly when he chooses the safety factor applicable at any point of the system. Sample applications of this method are given that illustrate the importance of a careful design of dipole feeding systems, and provide information about the limitations of curtain antennas and the performance which can be expected. >

New high efficiency 500 kW tetrodes for short wave broadcast

Abstract: Two 500-kW tetrodes, developed for shortwave broadcast service using computer-aided design (CAD) techniques are presented. The two tubes are similar, one having pyrolytic graphite grids and the other Y-3 grids. The tubes are interchangeable and have similar operating parameters. Cooperation between transmitter designers and tube designers facilitated the fulfilling of requirements established by the Voice of America for it's new generation of efficient shortwave international broadcast transmitters. Tubes are now operating in the model 420B transmitter at frequencies between 3.9 and 26.1 MHz at the Voice of America site in Greenville, North Carolina. The tubes operate interchangeably as the power amplifier tube, or the pulse duration modulator tube, and they have multiphase water-cooled anodes rated at 400 kW, low internal inductance and capacitance, mesh-thoriated tungsten cathodes, and two choices of grids, either platinum-zirconium-coated molybdenum wire or laser-machined pyrolytic graphite. >

Shortwave propagation prediction methodologies

Abstract: The status of ionospheric-propagation prediction models is examined, with particular emphasis on the use of these models by the shortwave-broadcast community. Their stand-alone capability for forecasts is found to be limited by the use of monthly median, statistical averages of archived ionospheric data, as well as by the use of imprecise control parameter inputs, such as the sunspot number. A variety of developing technologies are discussed for improvement of prediction models. Improvement may result from observations of coronal holes and other relevant solar features for long-term and short-term ionospheric predictions. Also discussed are a variety of other ionospheric measurement schemes for short-term ionospheric predictions, such as the use of vertical-incidence, oblique-incidence, and backscatter sensing from space. The application of this class of measurements for adaptive HF broadcasting systems is discussed. Incorporation of ray-tracing into propagation calculations in the prediction model is also considered. >

High-power, broad-bandwidth HF dipole curtain array with extensive vertical and azimuthal beam control

Abstract: The design, construction details, and performance of a prototype high-power HRS 12/6/.5 antenna system covering the 6 to 26 MHz international broadcast bands are presented. The antenna has been developed, erected, and tested as part of the Voice of America modernization program to demonstrate the feasibility of controlling the horizontal and vertical apertures and beam directions of high-power, broad-bandwidth (2:1 frequency ratio) antennas. The antenna system provides 11 vertical slews, 15 azimuthal slews, and five azimuthal widths. The peak of the elevation pattern can be steered to angles of 4 degrees to 20 degrees above the horizon and the azimuthal beam can be steered up to +or-30 degrees with respect to boresight. Gains range from 16 to 31 dBi. Azimuthal beamwidths between -6 dB points range from 8 degrees to 75 degrees . The antenna is designed to handle the input power of one or more 500-kW double-sideband, amplitude-modulated transmitters. The antenna system has been designed using basic dipole and antenna switching modules from which smaller subarrays (HRS 2/6/.5, HRS 4/6/.5, HRS 8/6/.5, etc.) can be readily developed. The extensive beam control provided by the antenna system enables a shortwave broadcaster to use fewer antennas to reach the same audience. This reduces the land area of the station as well as its acquisition and operating costs. >

Application of coding and diversity to UHF satellite sound broadcasting systems

Abstract: Results are presented of a study of alternative means by which to reduce the required link margins in a satellite sound broadcasting system, thus improving the economic feasibility of the service and increasing the possibility of sharing a radio-frequency allocation with terrestrial services. Propagation models are presented that account for the effects of shadowing and multipath in the operating environments. Comparisons are made of the performance that results using time, frequency, and space diversity to moderate the effects of shadowing and multipath for vehicular and portable receivers. It is shown that space diversity has the broadest applicability in restoring the channel performance that would otherwise be degraded by Rayleigh fading channels and by quasistationary AWGN (additive white Gaussian noise) channels. Example link budgets are given for candidate satellite sound broadcasting system designs that use analog FM and digital modulation techniques. >

Signal-to-interference ratio statistics for AM broadcast groundwave and skywave signals in the presence of multiple skywave interferers

Abstract: The development of a statistical description of the signal-to-interference ratio (SIR) for AM broadcast groundwave and skywave signals in the presence of multiple skywave interference signals is presented. The analysis assumes that the interfering signal envelope amplitudes are Rayleigh-distributed random variables with a lognormal distribution used to describe the long-term variations of the sum envelope amplitude. The resulting statistical description is used to evaluate the SIR degradation for a number of interference exclusion formulas under consideration for frequency allocation purposes. The results show that adding four equal interferers, each at a level equal to 50% of a first interferer, degrades the 50% time SIR by a little more than 3 dB. >

High performance antenna systems for new VOA stations

Abstract: Advancements in curtain-type high-frequency (HF) broadcast antennas are reviewed. Novel high-performance antennas for the Voice of America (VOA) are described, including vertical and horizontal beam selections, performance measurements, effects of finite ground and hills, radiation hazard zones, and transmission lines. Specifications for antennas to be installed at four new VOA stations are examined. The designs provide substantial flexibility in radiation-beam characteristics with four vertical beam modes and seven horizontal beam angles. it is believed that the technique of selecting the optimum radiation beam for ionospheric propagation to VOA target areas will provide a substantial improvement in the performance. >

The results of WARC-HFBC (87): technical implications

Abstract: The planning principles and technical parameters that were decided at the 1987 second session of the World Administrative Radio Conference (WARC) for the planning of the HF bands allocated to the broadcasting service (HFBC) are described. These planning principles and parameters are intended for use in developing test plans to satisfy the world's high-frequency broadcast requirements. Those parameters that were modified at the second session of the conference are discussed toward obtaining a workable and universally acceptable planning system for shortwave broadcasting. With reference to the results of the planning exercises that were used as the basis of decisions at the second session, the likely impact of these decisions on the HF broadcast planning process is described. Some issues that are likely to concern the US broadcasters in preparation for the third session of WARC are summarized in conclusion. >

Satellite receiver technologies

Abstract: The technical issues pertinent to direct broadcast satellite(DBS) reception are elucidated, dividing them into system and component-oriented subjects. The former include the relationship of DBS and TVRO (television receive-only) systems, TVRO technology, scrambling technology, PCM audio systems, MAC systems and HDTV. The latter are classified according to the path of the signal, that is, an antenna, LNB, and a receiver. Future trends are projected both for systems and components. >

HE receiving antenna directivity patterns and gain for ionospheric propagation model predictions for shortwave broadcasting

Abstract: Elevation-plane relative directivity patterns of a 9-ft rod measured with the XELEDOP full-scale HF antenna pattern measurement system are compared with values assumed by the Voice of America (VOA) and the British Broadcasting Corporation (BBC). Values of such directivity patterns and gain for a 7.5-ft monopole with sixteen buried ground radials, measured at the same site, are compared with predictions of directivity and gain made with the numerical electromagnetics code (NEC). An extensive set of recommendations is offered, regarding the appropriate assumptions for the receiving antenna in ionospheric propagation prediction programs. >

Jamming to the HF broadcasting service

Abstract: The Institute for Telecommunication Sciences has been actively involved in an internationally coordinated monitoring program to determine the location of emitters of harmful interference (jamming) to the high-frequency (HF) broadcast service. four monitoring programs were undertaken between October 1984 and June 1986. The procedures that have been used and the results that have been obtained are summarized. The locations of the emitters that cause jamming to the HF broadcast service are shown and selected characteristics of the jamming environment are described. The degree to which jamming that is directed to certain broadcasters adversely impacts the performance of other broadcast services that operate on the same or adjacent channels as the targeted broadcaster is examined. >

Measuring television transposer intermodulation distortion

Abstract: The authors examine the behavior of the intermodulation (IM) level during one line period and propose a measuring method allowing the use of a standard or a modified color-bar test signal. The latter enables the nonlinearity of the transposer to be minimized in the line synchronization region, and this is shown to minimize vision/sound crossmodulation. Differential gain and phase can also be optimized. Measurements indicate that minimization of the IM level with the three-tone method often causes unacceptable IM limits at other colors. The measurement technique is based on sampling the demodulated color-bar signal for short intervals corresponding to a selected color. This allows the simultaneous measurement of IM level at seven different points on the transposer's characteristic. >

The German TV-Sat broadcasting satellite system

Abstract: The design concept, service and communication modules, and characteristics of the TV-Sat system are described. Also discussed are the solar array, propulsion and antenna modules as well as the high-power amplifier. A dual control system is used for the coarse pointing of the satellite's body (by infrared earth sensors) and the fine pointing of antenna reflectors. Fine pointing is done by an RF-sensor and 2 pointing mechanisms (APM). In the case of TV-Sat, 90% of the power is required by the payload; only the subsystems AOCS (attitude and orbit control system), TTC (telemetry, tracking and command system), and UPS are not dependent on the payload. The power required by these subsystems is supplied by the solar array structure with an output of 68 W/m/sup 2/ and 19.4 W/kg. The methods by which a high mean temperature is achieved and heat dissipation problems are examined. In-orbit tests with TV-Sat 1 are presented. >

Methodology and computer tools to semi-automate assessments of shortwave broadcast coverage resulting from multiple transmissions

Abstract: A computer-assisted methodology, developed for using a point-to-point ionospheric propagation and communications system performance model to assess shortwave broadcast coverage, is presented. The listening area is approximated by a set of geographic coordinates (test points), and the required power gain (RPRG) for the link from each transmitter site to each test point is computed using the IONCAP ionospheric communications analysis and prediction program. The broadcasts may originate simultaneously from a single site or from multiple-transmitter sites (i.e., multicast). Figures of merit are assigned in terms of the RPG values, and area coverage statistics are computed for the simulated broadcasts. Three interactive computer programs were developed to permit a semi-automated multicast broadcast coverage analysis using IONCAP and a computerized equipment database. They are: propagation parameter set-up program; transmission plan set-up program; and multicast analysis program. >

Pilot aided techniques for system caused phase jitter cancellation

Abstract: A pilot-based method of extracting and cancelling system caused pilot jitter (SCPJ) in broadcasting systems is introduced and analyzed. It was demonstrated that, by using a wideband pilot extraction system instead of the frequently used minimal bandwidth one, the system performance can be improved considerably. Analytical results for the CNR degradation of a 16-QAM system operated in the presence of sinusoidal SCPJ were obtained as a function of the extraction filters bandwidth, as well as their amplitude and group delay distortions. It was shown that to achieve efficient SCPJ cancellation, it is important to compensate for both of these distortions. However, as far as implementation issues are concerned, group delay distortion seems to be a more prominent source of degradation. >

An analysis of queuing strategies for SCA data broadcast systems

Abstract: Subcarrier audio channels (SCAs) are used to support a wide-area data communication system. Text or data messages can be transmitted nationally using satellite delivery, and locally using FM broadcasting stations' subcarriers. The time delay that messages experience in the national buffer at the satellite head-end or the local buffer is examined. The delay for various throughput data rates is evaluated to identify an optimum range for this capacity. A realistic set of messages statistics is developed to model SCA traffic. Three different queueing strategies are used to examine the delay that messages obeying these statistics would experience: first-come-first-served, fixed-priority, and delay-dependent priority. It is shown that, as the throughput is increased, the effect of priority on the system is less discernible. As the output capacity is decreased, the effect of a priority structure can be seen to enhance traffic flow. Total message time delay is examined using a delay-dependent priority scheme. Results indicate that the choice of an appropriate queuing strategy will enhance the flow of priority message traffic. >