Site Records


Site Name: RAF Holmpton/Patrington ('VQJ') GCI R3 ROTOR Radar Station

Rysome Lane
Holmpton,
Yorkshire

OS Grid Ref: TA365227

[Source:RAF Holmpton Archive & Nick Catford]


KELVIN HUGHES PHOTOGRAPHIC DISPLAY UNIT


The Kelvin Hughes plotting table at RAF Buchan


Photographic projection unit - this photographs a radar display onto film and projects it to the underside of the plotting table via mirrors

The Kelvin Hughes Photographic Projector; consisted of equipment that could record the radar image on 35 mm film, develop, fix and dry the image and then project it up on to the plotting table in the control room on the floor above. The displayed image was one minute behind real time. The PPI image from a high intensity cathode ray tube was projected on to the film through a focusing lens. Each revolution of the radar antenna took 15 seconds and it took this time to expose the film to a full revolution. At the end of the sweep, the frame would be moved on to be developed, whilst the next frame was exposed. When the frame moved on at the end of the next sweep the image was fixed, it then moved on again to be dried.

Finally the frame moved on once more where it was projected, via a mirror, to the underside of the frosted glass plotting table on the floor above. Meanwhile the next frame to be exposed has been following on through the process, so at the end of the next revolution this frame was projected, 15 seconds after its predecessor. As frame after frame was displayed on the map the plotters in the pit could place markers on the map to indicate friendly or hostile aircraft.


A slightly different unit to the above picture shown in situ with the
rear of the second unit to the left and the mirror in-between.

 

[Source: Nick Catford]

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Last updated 19th January 2005

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