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I am indebted to my colleague, Mr. Ian Hopley, for drawing my attention to the following article, reproduced from The Post Office Electrical Engineers Journal, Vol.38, Part 4, January 1946. I imagine that this journal must have been highly sought after by Post Office engineers of all disciplines, as the contents were well written and the subjects positively eclectic, ranging from the "Calculation of soil load bearing properties for cable chamber construction" to the following article;


Post Office Equipment for Radar

P. A. Marchant, A.M.LE.E., and K. M. Heron, A.M.I.E.E.

U.D.C. 518.5 :621.395.658 621.392.43 :621.396.67 :621.395.342

The article describes some of the interesting equipment developed by the Post Office and used by the Air Ministry at Radar stations.

Introduction.

When the first secrets of radar were made public, interest was largely focused upon its use for the detection of aircraft. With a knowledge of the first principles of radar it is undoubtedly this application that comes readily to mind. It was, in fact, the obvious channel for early development quite apart from strategical necessity.

The Air Ministry was not slow to appreciate the immense value of radar to augment the existing air defence reporting scheme and to extend the area of observation considerably beyond the shores of Britain. Accordingly, the development of a chain of reporting stations was projected in the very early stages, and was, in fact, in operation at the outbreak of war.

The vital link, as with all previous reporting schemes, was communications. It was inevitable, therefore, that the services of the Post Office should be enlisted at an early stage. But this was not all. There were other problems which, it was realised, could be readily solved by the use of telephone switching technique and the assistance of the Post Office was sought in the development and production of the equipment required.

Historical Survey.

Co-operation was first established in 1938 when the Air Ministry approached the Post Office regarding the development of equipment for use with the east coast chain of reporting stations. Development proceeded with all speed, and by early 1940 it was possible to provide equipment for all stations covering likely areas of approach. From 1940 onwards an ever increasing Air Ministry programme had to be met. The number of existing types of stations was increased to cover all areas. New types to meet the constantly changing operational needs were projected, developed and established almost in one operation.

It was not long before the spotlight of urgency changed from reporting stations to interception stations and thence to controlling stations concerned primarily with offensive operations. During the same period the programme of mobile stations, both for home and overseas use, increased considerably. In all these stations P.O. equipment had to be installed, varying from small keyboards to racks of automatic equipment, etc. Finally the records showed that 66 different types of stations had been dealt with and a grand total of 365 fixed and 644 mobile stations had been equipped.

Space does not permit of the description of the communications equipment, and the remainder of the article will be devoted to a brief outline of some of the more interesting items of special equipment which were produced.

The Calculator

However impressive the towering aerial arrays, high powered transmitters and bays of receiving equipment at a main reporting station might be, it is with the final answer that the operational side are concerned and how soon that answer can be transmitted to a control centre in a readable form. The electrical calculator was developed to obtain this final answer from the radar information.

The Problem.

The message to be transmitted to the control centre is required in the following form

(a) A map reference position.
(b) A height in feet.
(c) A number of aircraft.

The map reference is required in the form A1234, where the letter defines a particular map square of side 100 km., the first two figures represent the distance in kilometres along the "x" ordinate and the last two the distance along the "y" ordinate, within that square.

Fig. 1 represents the face of the cathode ray tube on the radar receiver. The length of the trace represents the full range of the station (e.g. 300 km.). The deflection E is an echo denoting the presence of aircraft at a range "R" from the station.

The angle of bearing (Gq) or angle of elevation (Ga), dependent upon whether bearing or height measurements are being taken, is given from the angular setting to which the gonio control must be rotated for E to be at minimum amplitude. The value of R can be read directly from a scale along the trace. The number of aircraft can be estimated only from the formation of the echo.

The values of Gq, Ga and R can be read directly, but require conversion into message form. A further complication is that neither Gq, nor Ga is a true value and must be corrected to the true angles of bearing q, and elevation a respectively. The correcting factors which must be applied are dependent upon the surrounding terrain and thus upon the angle of bearing. They are values which must be predetermined for each station.


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Updated 06/11/2001

Constructed by Dick Barrett

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ęCopyright 2000 - 2002 Dick Barrett

The right of Dick Barrett to be identified as author of this work has been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.