The Telecommunication Journal of Australia Vol 29 No 3 1979
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29/3 THE TELECOMMUNICATION JOURNAL OF AUSTRALIA · Volume 29, No. 3, 1979 ISN 0040-2486 CONTENTS Radio-Relay System Path Survey Techniques - Part 2, Survey Methods · N. L. WAIN .............. 171 Touchfone 12 A.A.RENDLE .. .......... 181 Manual Assistance in Australia - Its Future Role J. E. LOFTUS and C. W. A.JES SOP - ..... ... 187 Data Transmission Developments and Public Data Networks NGUYEN Q DUC 194 X.21: An Interface Between Data Terminals and Circuit Switched Data Networks. G. J. DICKSON . 206 A Buck/Boost No-Break Telephone Power Supply N. K. THUAN ... 214 A Solid State Digital Speaking Clock G. R. BARBOUR ......... 224 Concentrator Subscriber Radio Services G. BANNISTER .... 233 Automatic Call Distribution System - ASDP 162 P.A. BROWN and D. W. CLARK ... 245 Other Items New State Manager for Tasmania 180 CCITT Working Party on Languages for SPC Exchanges 186 Correction Vol. 29, No. 2 193 Obituaries: Mr C. J. Griffiths and Mr C. Melgaard 205 Retirement of Mr F. A. Waters 213 Defence International Communications System . 223 How to Understand Frequency Counter Specifications 232 Contract issued for Carfone System 255 COVER RADIO - SYSTEM SITE SURVEY Abstracts · · · · · · · · · · · · · · · 263 The Telecommunication Journal of Australia The Journal is issued three times a year (February, June and October) by the Telecommunication Society of Australia. The object of the Society is to promote the diffusion of knowledge of the telecommunications, broadcasting and television services of Australia by means of lectures, discussions, publication of the Telecommunication Journal of Australia and Australian Telecommunication Research, and by any other means. The Journal is not an official journal of the Australian Telecommunications Commission. The Commission and the Board of Editors are not responsible for statements made or opinions expressed by authors. Residents of Australia may order the journal from the State Secretary of their State of residence: others should apply to the General Secretary. The current subscription rates for both Telecommunication .Journal .of Australia and Australian Telecommunications Research are shown on the inside back cover of this issue, A.II rates are post free (by sur• face mail). Remittances should be in Australian currency and made payable to the Telecommunication Society of Australia. Editors of other publications are welcome to use .not more than one-third of any article, provided credit is given at the beginning or end, thus, "The Telecommunication Journal of Australia". Permission to reprint larger extracts or com• plete articles will normally be granted on application to the General Secretary. Information on how to prepare and submit manuscripts and contributions for the Journal is available from members of the Board of Editors and their outposted representatives. Membership fees and subscription orders should be addresed to: WITHIN AUSTRALIA The State Secretary, Telecommunication Society of Australia, Box 6026, G.P.0 .. Sydney, N.S.W. 2001. Box 1183, G.P.O., Adelaide, S.A. 5001. Box 18020, G.P.O, Melbourne, Vic. 3001. Box T1804, G.P.0 .. Perth, W.A. 6001. Box -1489, G.P.O., Brisbane, Old. 4001. Box 10,000T, G.P.O., Hobart, Tas., 7001. OVERSEAS APPLICATIONS The General Secretary, Telecommunication Society of Australia, Box 4050, G.P.O., Melbourne, Victoria, Australia, 3001. BOARD OF EDITORS L. M. MITTON, Editor-in-Chief L. N. CUNNINGHAM R. A. CLARK L. A. TYRRELL N. A. CAMERON A. CARUANA D. f!,.. GRAY R. W. E. HARNATH B. A. ENDEHSBEE M. RHEINBERGER G. MOOT H. P. GUTHRIE Production: D. M. WHITESIDE Representatives New South Wates Victoria Queensland J. F. McCARTHY A. MORTON F. M. SCOTT Western Australia Tasmania South Australia G. WHITE 0. C. WINTER R. J. SHINKFIELD General Secretary: W. FITZSIMONS ADVERTISING All inquiries from prospective advertisers should be directed to: ADVERTISING MANAGER, Box 4050, G.P.O., Melbourne, Australia, 3001 Telephone (03) 630 6259 Radio-Relay System Path Survey Techniques Part 2, Survey Methods N. L. WAIN, A.R.M.I.T. This second and concluding part of a study of radio-relay system survey methods outlines the techniques commonly employed to obtain the path parameters necessary for reliable design of transmiss• ion performance and cost estimation of proposed systems. Common survey practices are covered together with some of the more economic and novel methods used for small capacity and single channel systems. INTRODUCTION The survey techniques to be described include the nor• mal survey practices employed by Telecom for the design Part 1 of this article gave a brief outline of the of long-haul broadband radio-relay systems together with relationship between environment and propagation some of the more economic and novel methods used by characteristics encountered on line-of-sight radio-relay system designers for predicting path performance of systems. The dependence of the system performance on small capacity and single channel systems. the ray-line clearance of the system paths was emphasised and led to the need for a survey of each path OBJECTIVES OF THE SURVEY to establish accurately the necessary tower and antenna The survey provides information upon which accurate heights for the system to achieve the desired perfor• estimates of system performance and overall costs can mance. be made. The clearance criteria outlined in Part 1 are not usually The principal parameters obtained from a survey in• applied to small capacity and subscriber radio systems clude: operating in the VHF and UHF bands because the larger • The co-ordinates of the station mark (with respect to Fresnel radii would require very high antennas on a the Australian Geodetic Datum, AGO), identified by a typical system and consequently increase the cost of peg indicating the position of the proposed tower or antenna support structures beyond the economical limit mast. for such a system. The propagation performance at the • The site R L {reduced level), i.e. the elevation of the lower frequencies is less susceptible to anomalous station mark with respect to the Australian Height tropospheric behaviour than it is in the SH F bands, so Datum {AHO). reducing the incidence and magnitude of fading at these frequencies. Also the noise performance criteria for small • The relative elevation of topographic features along the capacity and subscriber systems are less stringent than path. those stipulated for broadband systems thus making it • Path length and distance to significant features along practicable to design paths with low ray-line clearance. A the path. further constraint is that these systems often have the • The true bearing of the ray line and its angular radio equipment co-sited with subscriber or switching separation from significant features in the vicinity of equipment at locations not ideally situated from a radio the path. point of view. In such circumstances the paths may be • The height and density of vegetation below the ray severely obstructed by the intervening terrain in which line. case the system design is optimised for economy and • The extent and slope of likely reflection areas below noise performance from a map study, field inspection and the ray line. propagation measurements, eliminating the need for an • An estimate of access road construction and power expensive detailed survey. supply costs. WAIN - Radio Path Survey Techniques - Part 2. 171 The information obtained from the survey is collated (EDM) in which the phase shift of a modulated light by the Surveying Authority and is used to prepare the fol• beam transmitted over the path to a prism reflector lowing documents: and back to the sender is interpreted in terms of path • Route plan length. This instrument gives a direct read-out of path length in metres and is able to resolve distances up to • Path profile drawings 1.5 km. accuracy is of the order 1: 200 000. The • Near-end detail plan and profile drawings geodimeter is used in levelling traverses and is shown • Site information drawings in Fig. 10. • Site contour drawings SURVEY METHODS FOR BROADBAND SYSTEMS Examples of these drawings may be found in The field survey of a broadband route can be sub• Reference 1. divided into three phases: The Surveying Authority is the organisation carrying • field reconnaissance out the survey aspects in accordance with Specification 1214 ( Reference 1) and in most cases is the Drafting and • detailed traverse Survey Section in the State Administration of Telecom. • site and road survey However. when specialised work is required, for instance An outline of these functions follows. photogrametry, the work is contracted to a competent authority equipped with the necessary expertise and FIELD RECONNAISSANCE facilities to conduct the survey. Close liaison between the The first requirement of the survey is to establish that design engineer and the Surveying Authority is essential a workable route can be provided using the sites selected to monitor progress and advise of additional work as the in the map and feasibility study. survey information is analysed. This involves a field reconnaissance of the route in which each path is roughly profiled using barometric levelling and/or limited theodolite traversing depending COMMON SURVEY INSTRUMENTS on the roughness of the terrain. It is during this phase Some of the more conventional instruments used to that Civil Engineering advice on road cost estimates is re• survey radio paths include: quired and the basic route of access roads is determined. • Heliograph. a device using a mirror system to reflect the sun's rays in a continuous beam on a desired bear• ing and so serve as a reference for a distant observer. • Theodolite, an instrument for the accurate measurement of horizontal and vertical angles by means of a telescope capable of rotation in the vertical and horizontal planes. Circularly graduated plates are used to measure the amount of rotatory motion when the telescope is sighted on successive targets. • Tellurometer. an electronic instrument used to measure the length of survey lines for distances up to 60 km by the phase shift in a SH F transmission propagated from one end of the path to the other and back.