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Subcarrier Transmission of Narrowband Video Signals Offers Exciting Promise.

When the opportunity to use satellite subcarrier channels is available, there is a corresponding opportunity to use this channel to transmit video signals. At first glance this may not seem right, given video's large bandwidth requirements, however, transmitting still video images over a subcarrier channel creates an economical and effective use of a satellite or FM radio channel. The transmission of still video images is one of the many ways to exploit subcarrier channels; others include radio paging, data transmission and specialized program services. This article details the transmission of high-quality color images over satellite and/or FM subcarrier channels.

A bandwidth of 7.5 kHz is sufficient for the transmission of a single field, NTSC-like, color video image in eight seconds. Broadcast television, on the other hand, uses a bandwidth of over 4 MHz to deliver a single-field video picture in 1/60th of a second. Since the satellite or FM subcarrier channel bandwidth is considerably smaller (by a factor of over 500:1), the transmission time for the same amount of video information (a single field video picture) is proportionately longer: eight seconds, compared with 1/60th of a second. At this rate the picture can be seen building up across the video screen. These video pictures are limited only by their inability to display motion. Like a 35-mm slide, a still video image conveys large amounts of information and has a strong impact.

The potential applications are varied. Educators can use this broadcast medium for distant education, to remote classrooms or directly into the homes of the students. Lectures and visual instruction can be delivered to large audiences quickly and conveniently. Interactivity can be obtained via telephone, and can also employ the return transmission of video images when necessary, but usually at a slower rate due to the more limited bandwidth. Student or in-service employee training is also part of the educational potential for "freeze-frame video." Information that is required to be distributed from a central source to many locations can effectively use subcarrier.

Advertisers have available to them a mass marketing tool for a wide variety of products and services. Storecasting is a prime example. By placing receivers, monitors and, as required, speakers in stores throughout a satellite footprint or FM broadcast area, customers can view a wide variety of information. In-store advertising and promotion would be the primary objectives of storecasting, however, its scope can be broadened to include services such as news, weather, community and public-service information. With this sort of information mix, viewer interest can be heightened for what becomes a new technique for information dissemination. Storecasting could also be used for specific department promotions on a rotating basis. The meat or produce departments might advertise single products on an unattended video display for the customer to review at his or her convenience.

The nationwide coverage provided by satellites, coupled with the small bandwidth requirements of freeze-frame video, make them a viable technology for the delivery of video information. Either a single-channel-per-carrier (SCPC) or a subcarrier of a wideband video channel can be used, depending on costs and availability. The expansion of markets from local and/or regional to national or international is a strong incentive to employ satellites for delivering information to meet business goals.

The excellent local area coverage provided by FM subcarrier is the key to its use. Either the 67-kHz or 92-kHz subcarrier channels are recommended for video picture transmission, while related audio programming can be transmitted on the remaining channel for more-effective communication. This point-to-multipoint communication can put needed information into many locations immediately. Hard-copy equipment can be connected at the receiving end for a printout of the

A video camera, monitor, video-tape recorder and narrowband video transmitter are the basic components for program production, whether the objective is education, advertising, training or a pilot project. A computer-controlled digital disk memory can be used as a sophisticated replacement for the tape recorder. Numerous pictures can be stored on disk in advance for ease of production. Production flexibility can be gained by producing program in advance or on a real-time basis. For the simplest transmitting capability, only the camera, monitor and transmitter are needed. Each receive site will require an antenna, satellite or FM subcarrier receiver, narrowband video converter and one or more display monitors, plus audio if required. Satellite or FM subcarrier signal carriage costs must, of course, he negotiated with a satellite company or FM station licensee, and costs may vary widely.

Cost-Effective Medium

The costs of single-frame video subcarrier communication are very reasonable when compared with other forms of video communication. A narrowband video converter for the transmitter site will cost $12,000, an accompanying color camera and monitor about $7,000, a narrowband receiver about $5,000 and the associated antenna, SCA receiver and monitor approximately $1100. In many cases, still-picture video is analogous to the print media. Now educators, advertisers and news providers have a new, yet accessable resource for the delivery of information. Low transmission costs, combined with low production costs, make subcarrier communications an ideal format for the distribution of specialized programming.

Satellite or FM subcarrier transmission of narrowband video images offers exciting promise for business, advertising, education and a host of other potential applications. The ever-growing need for visual communication can be met in an effective and economical manner by this system. Low transmission and production costs, coupled with the ability to serve a wide population base, makes this technology a strong choice for specialized video communications.
COPYRIGHT 1985 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1985 Gale, Cengage Learning. All rights reserved.

Article Details
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Author:McIntosh, D.
Publication:Communications News
Date:Mar 1, 1985
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