Showing papers in "IEEE Transactions on Broadcasting in 1981"

Numerical Computation of the Reradiation from Power Lines at MF Frequencies

Abstract: The encroachment of "civilization" on the site of a medium wave broadcasting array can give rise to distortions of its radiation pattern resulting in inadequate coverage of the service area, or even in the violation of licensing provisions. The radiation pattern distorts because RF currents are induced by the broadcasting antenna's field on any large metallic structures such as a highrise building or a high-tension power line. If the structure is resonant, these currents can be large and the reradiated field can be strong. This paper uses modern digital computer techniques to calculate the field reradiated from a power line near an AM broadcasting tower. The current distribution on the towers and "skywires" for a uniform power line is shown to exhibit distinct "off-resonance" and "resonant" behavior. The frequency dependence of the reradiated field is found to be simple loop resonance for a uniformly spaced power line, and so is a super-position of the resonant behavior of loops of many sizes for a complex site. The computer model is applied to analyze the azimuth pattern for a complex site near Hornby, Ontario where two power lines come close to an omnidirectional antenna. The computations are compared with scale model measurements. Since a perfectly conducting ground was used in the computations, the method may help to estimate the upper bound on the distortions of the azimuth pattern which could arise from the construction of a proposed power line near an existing broadcasting antenna.

A Technique for Digital Information Broadcasting Using SCA Channels

Abstract: This paper describes a simple technique using the SCA (Subsidiary Communications Authorization) channel authorized for use in FM and TV broadcasting to provide a one-way digital transmission channel for teletext-type service. The channel is transparent to data format. Preliminary field test results for a 9600 bit/second channel are also presented which show average error rates of less than 1 in 106.

A Video Codec Transmitter

Abstract: The transmitter of a video codec system is designed and realized in ECL hardware. This video codec system is capable of carrying one commercial NTSC color television channel with a program audio channel at a rate of 42.9 Mb/s. The transmitter interfaces with a DPCM processor. The transmitter removes the horizontal blanking interval from the composite television signal, converts the quantized difference signal from the DPCM processor into 4/8-bit dual length code and buffers the codes for constant rate transmission. A line synchronization code is multiplexed with audio and video codes to form a serial data link at 42.9 Mb/s. This can be transmitted on a T3 (44.7 Mb/s) digital carrier. The transmitter is composed of four functional units: controller, coder, buffer and multiplexer. This paper describes the design, layout, testing and evaluation of the high speed digital system that results in 2 to 1 data compression of the digital video.

The First Candelabra for Circularly Polarized Broadcast Antennas

Abstract: A study of a circularly polarized (CP) television multiple antenna installation shows that improved measurement and theoretical techniques are required to model the scattered horizontal pattern circularity and video response in a candelabra. Previously developed guidelines for horizontally polarized antennas in a candelabra are inadequate to describe the expected performance of CP antennas in the same configuration. Results of calculations and measurements of model CP antennas for a Columbus, Ohio candelabra are included.

Television Broadcasting at Microwave Frequencies

Abstract: Over 125 Multipoint Distribution Service (MDS) transmitting stations have been constructed over the past seven years. Each of these stations is equivalent to a low power television broadcast station operating on a microwave frequency at approximately 2,150 MHz. The problems encountered in the design and construction of an MDS station differ markedly from a VHF or UHF television station. The propagation characteristics, likewise, are significantly different than for either UHF or VHF frequencies. The solution to the problem of effective coverage and reception throughout a service area requires innovative designs and techniques, and these are described.

Satellite Beam Optimization for the Broadcasting Satellite Service

Abstract: In view of the forthcoming ITU Regional Administrative Radio Conference for the planning of the Broadcasting Satellite Service at 12 GHz for the American Continent to be held in 1983, there is a need for a means to transfer the service quality requirements for a Broadcasting Satellite Service into a consistent set of satellite and receiving terminal parameters.

Broadcasting Satellites Power Blackodes from Solar Eclipses Due to the Moon

Abstract: The power supplied to a satellite by its solar cell panels can disappear when sunlight is blocked, or severely diminish when partially shadowed. Solar eclipses due to the earth are one cause for such outages. Eclipses due to the moon are the other. Occurences of the former are regular while the latter happen at irregular intervals.

Design and Installation of Limited-Area AM Broadcast Systems

Abstract: This paper discusses the design and installation of low-power AM broadcast systems using power-line-carrier techniques. Such systems permit coverage of listeners in dormitories and similar structures. This discussion covers technical aspects of the propagation medium, typical design objectives, and related economic considerations. Spectrum-regulation issues pertaining to North America are covered, with related matters like selection of operating frequency and control of undesired radiation. By supplementing the rather meager technical literature on this topic, this discussion may prove useful to the broadcast engineer who is called upon to design or expand one of these systems.

Design Considerations and Performance of Circularly Polarized Tv Antennas

Abstract: This paper discusses those concepts and objectives which are important to the broadcaster considering circular polarization The results of polls taken among viewers as to the quality of CP reception are presented Achievements in design, development and fabrication of CP hardware are also described

A New Technique for Measuring FM & TV Antenna Systems

Abstract: Described here is a measuring system using a computer controlled network analyzer that allows observation of FM and TV broadcast antenna systems. Impedance measurement may be made at any point in a broadcast antenna system where access is possible. Most notably, the VSWR characteristics of an antenna on a tower may be measured from the ground without the effects of the transmission line. Measurement accuracy is 0.1 DB and 0.5 degree return loss with excellent repeatability. The system is suitable for field use allowing evaluation of the antenna and other parts of the RF system.

Random Noise Interference and Possible Solutions to its Effects on Image Resolution and Gray Scale

Abstract: In this paper we report the effect of random noise interference in various portions of the video band spectrum' and attempt to model the human visual mechanism for resolving image in the presence of noise. Broad, narrow and mixed bands of white noise distribution effects throughout the video band are investigated. Good agreement results between the experimental data and predicted performance from computer simulation models. The analysis indicates that noise equalization, by pre-emphasizing and deemphasizing a certain portion of the video, results in a considerable improvement in resolution and gray scale of the image.

Toward Improved Control of Medium Wave Directional Arrays

Abstract: Relatively few types of variable power division circuits have been used in medium wave directional antenna feed systems, most of which suffer phase variation as the power division is adjusted. This paper discusses a class of circuits which can be used to implement a phase invariant adjustable power divider. Also discussed are variable phase shifters which have limited effect on power distribution. These features can simplify the original tuning and possible periodic maintenance. A computer analysis of the probable performance of such devices is presented. The associated problem of system analysis is discussed, particularly the inclusion of the effects of the antenna element coupling. To this end a lumped passive element model for a generalized linear reciprocal N port is presented.