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 Post Office Equipment for Radar

There are therefore the following requirements to meet before the information given is available in message form.

(a) Bearing - to measure Gq - apply correction to obtain q - evaluate R sin q and R cosq to obtain the answer in the form A1234.
(b) Height - to measure G
a - apply correction to obtain a - eva1uate R sin a to obtain the height.
(c) A further requirement was that (a) and (b) should be determinable for any one of eight different aerial systems, each having different G
q and Ga correction factors.

Circuit Principles.

The underlying principle used to perform these calculations was that the banks of motor uniselectors acted as squared paper, the wipers corresponding to the abscissae of the curves R sin q, etc., and positions around the banks representing the ordinates. Fig. 2 shows a simplified schematic of the arrangements for the determination of map references.

When the range and bearing controls have been set, the depression of a start key causes the G switch to rotate to the Gq marking. Gq is corrected by the translation field to true q. Switch A then rotates to true q. Wipers of the RC switch corresponding to sin q and cos q are selected by the A switch. The banks of the RC switches are wired such that all contacts having the same values of R sin q or R cos q are connected together and wired away to the banks of X and Y switches. The RC switch rotates to the value of "R" and thus the products of R sin q and R cos q are selected. The X Switch then rotates to the R sin q marking and the Y switch to the R cos q marking. The function of the X and Y switches is to convert the values R sin q and R cos q into the form A1234 and light corresponding lamps on a display.

The height cycle is very similar except that the corrections to be applied are somewhat more complicated and that the R sin a values can be wired directly to the lamp display.

The number of aircraft is included in the lamp display, the appropriate lamps being lighted by the depression of keys on the receiver.

The equipment was arranged as shown in Fig. 3. Siemens No. 17 motor uniselectors were used to obtain the high speed of searching and the bank capacity required. A third rack was included at a later date to provide for an increase in facilities.


As the field of application of radar widened, the increase in operating personnel and reporting circuits was such that a reduction in both became desirable. A scheme was therefore projected to enable aircraft plots to be automatically recorded at the reporting station, forwarded to the filter room in the form of a teleprinter message, and then converted into a voice message, to be received as such by the filter room plotters.1

Increased efficiency was expected to result at the reporting station and a reduction in the number of physical circuits by the use of multi-channel working. For various reasons the sending and filter room portions of the scheme were abandoned and only the equipment at the reporting end was completed. This equipment was known as the message recorder and incorporated all facilities for transmitting to line.






1P.O.E.E.J. Vol. 38, page 109.

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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.