Radar and Oscilloscopes
A practical commercial radar display requires a signal from a rotating aerial to produce a picture on the cathode-ray tube. It is, therefore, seldom possible to use fully practical radar equipment in studio productions.
Radar scanner
To simulate a working radar it is possible to have a ‘display’ which is scanned by a rotating radial ‘beam’ of light. This can be achieved by using a rotating disc of clear plastic sprayed with black paint in such a way that it fades gradually from clear to opaque. The opaque section should cover at least one third of the disc, while the clear area should be in the form of a narrow line.
The disc is fitted to the extended spindle of a gear box driven by an electric motor. Alternatively it can be driven by a motor via belts and pulleys.
In front of the disc is the display. This is also a sheet of clear plastic sprayed uniformly with black paint to render it opaque. The display (usually in the form of a map) is scratched through the paint leaving a clear, brilliant outline. Next comes a sheet of tracing paper and finally another sheet of clear plastic.
A light placed behind the disc provides a typical rotational scan followed by the characteristic fade out. The effect is enhanced by putting a yellow or blue-green gel in front of the display.
Where ‘moving’ blips are required a number of clear areas can be covered and uncovered in turn by pulling sliders behind the main display disc. This activity is carried out during the period when the area is blacked out.
Oscillographs
Oscilloscope patterns, provided that they do not have to show varying patterns, can be simulated with a double mirror partially sprayed on both sides with black paint. The paint is sprayed in such a way as to fade out the trailing edge of both mirrors.
A light reflecting from the rotating mirrors falls on a display which has been prepared by spraying clear plastic with black paint and then scratching out the area required for the simulated trace. The front is covered with tracing paper and coloured gel.
Mock traces
A motorised, revolving bent wire, painted white and set in a black hole gives the impression of a realistic trace if not seen too closely. A useful gimmick for science-fiction sets.
1. Parts for a motorised radar scan simulator
a, Clear plastic front, b, Diffuser screen, c, Clear plastic with scan pattern, d, Graduated disc, e, Motor.
2. Parts for a simulated oscilloscope display
a, Clear plastic front, b, Diffuser screen, c, Clear plastic with trace pattern, d, Mirror drum, e, Motor.
3. A ‘busy’ display to use in the background
a, White painted bent wire in black box. b, Motor.