Rotor Radar System

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Rotor radar system

Radar Type 13 CMH

Type 13 CMH height finder (photo - Watching The Skies)The Type 13 CMH (Centimetric - Height) was the R.A.F.'s first centimetric radar and was developed in order to improve height information at GCI stations.

Development started in 1942 using two cheese antennae mounted together vertically to give an aperture of 20 feet by 3 feet and employing Naval Type 277 transmitter and receiver. The narrow vertical beam of 1.5o was nodded vertically from -1o elevation to +20o elevation at 6 cycles per minute. The horizontal beam width was 7.5o.

A range/angle of elevation display was used to measure the height of an aircraft which had been selected and towards which the Type 13 had been turned by remote control. The Type 13 or CMH set was put into production in March 1943 but the requirement for the Type 14 diverted effort. The first Type 13 Mk II was operational in early 1944.

Type 13 Mk5 height finding radar (Photo: via Subterranea Britannica Research Study Group )The Type 13 Mk III and IV were similar to the Mk II but the Type 13 Mk V had a much improved aerial. The improved aerial consisted of a reflector made up of 0.5 inch rods forming a paraboloid cylinder and was fed by a slotted wave guide. The resulting antenna was similar to that employed on the Type 14 Mk VI though somewhat smaller. The Type 13 Mk V antenna measured 20 feet by 5.5 feet. The performance of the Type 13 was very similar to that of the Type 14. (Watching The Skies). 

The typical characteristics of the Type 13 were:

Peak power:

500 Kw

Pulse length:

0.6 or 1.9 us


500 pps


3 GHz (10 cm)

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Updated 30/08/00

Constructed by Dick Barrett


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ęCopyright 2000 - 2003 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.