Saturday, 27 August 2011

Listening Ears to Radio Waves


Denge Sound Mirrors - photo by Paul Russon, reproduced under Creative Commons Attribution Share-alike license 2.0

These ‘listening ears’ or ‘sound mirrors’ were built in the 1920s and 1930s They were experimental as can be seen by the the different shapes of each of the three reflectors: one is a long, curved wall about 5 m (16.4 feet) high by 70 m (230 feet) long, while the other two are dish-shaped constructions approximately 4–5 metres across. Microphones placed at the focal point of the reflectors enabled a listener to detect the sound of aircraft far out at sea.

Unfortunately, you can no longer visit the site except as part of a guided tour and we were unable to arrange one when we passed through in 2010 while visiting Dungeness.

Radar (Radio Detection and Ranging) was developed for military purposes during the second world war – don’t worry, you are not getting a dissertation on the subject, you can Google as well as I can!  We visited The Royal Airforce Air Defence Radar Museum.  I’ve typed in its full name as there are several Radar Museums in the area.


It is difficult to believe that The Battle of Britain was controlled in rooms like this with young women pushing little markers across a plan.  The site was operational till 1993 – with many upgrades and the Cold War Operations Room looks like a smaller version of NASA or Dr Strangelove.


One of the great names in early radar development was Marconi and I grew up near this tower at the research station just outside Chelmsford.  It is a ‘Chain Home’ tower, that being the code name for the ring of coastal early warning systems built along the east and south coasts.  It is the only fully intact system left and celebrated 70 years from the Battle of Britain in 2010.

Last but not least, Alan saw a demonstration of this website and it is his latest toy.  I have been known to visit the site myself – purely in the interests of research of course.


  1. That's really interesting - surprising those things really worked.

  2. Some of the science museums have 'whisper dishes' on the same principle - there's one at the Exploratorium in San Francisco, I believe.


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