THE CATHODE RAY TUBE [Main Title]

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  • Title: THE CATHODE RAY TUBE [Main Title]
  • Film Number: AMY 230
  • Other titles:
  • Summary: A technical instructional film aided with animated diagrams which explains the principals of the basic cathode ray tube and its value as a basic electronic instrument for the measurement of high frequency signals. The film then shows how the cathode ray tube is a critical and integral part of any radar system
  • Description: In radio, signals of very high frequency are employed and it is necessary to have an instrument that will respond at such frequencies. Due to the mass and therefore the inertia of the moving parts of a mechanical device, they can only respond to frequencies of a few thousand cycles per second. The cathode ray tube does not suffer from this limitation because the moving part is a beam of electrons of negligible mass. It is invaluable in the study of radio since it will trace out signals accurately as high as ten million cycles per second. The history of the cathode ray tube over the past 50 years is reviewed and of the many developments, the television receiver is probably the most familiar. With the outbreak of war new devises were invented to detect aircraft and shipping and research concentrated on the development of radar in conjunction the cathode ray tube which is the heart of any radar system. An explanation of what a cathode ray tube is and how it works then follows and shows how the coating on the face of the tube can cause a moving spot to appear as a straight line. The cathode ray tube is similar to a thermionic valve and as such has a heated cathode, anodes, etc. A series of intertitles accompanied by film clips and diagrams explain each major component of the cathode ray tube. “Focussing” is controlled by the voltage at the second and third anode. "Time base”. When the input signal is independent of the time base and is applied to the vertical deflection plates (Y plates) it is said to be “free running”. If the two signals are not synchronised the trace moves along the screen. To prevent this the time base is triggered by the input signal. Fixed time base speeds are obtained by using a series of different value capacitors. “Electrical measurement”. The signal is applied to the Y plates and its position relative to the screen is noted, which is calibrated with known levels of voltage (or current). Instantaneous signals of a fraction of a second or less are recorded by a camera triggered by the signal. “Deflection and shift”. Two methods are available to deflect the beam, electrostatic (four plates) or electromagnetic (two coils). When the spot appears as a continuous line this is called the trace, and may be moved to any position on the screen by the X and Y shift controls. “Display of waveforms”. When the input signal is of high frequency the duration of the display on the screen can be 1/50 second or less. To make the trace visible to the eye, only one complete cycle is displayed, after which the spot returns to the beginning to repeat the process. Thus the final signal comprises many such retraces superimposed. “Radar” Radar (Ra radio, d detection, a, and r, ranging) is based on the reflection of radio waves, analogous to sound waves. The principals of radar are explained and the film depicts various types of antennae and how the transmitted and received signals are connected to the X and Y plates of the cathode ray tube. The X axis is calibrated in terms of distance, and is achieved with an oscillator. In operation the target is associated with a blip on the horizontal trace. The amplitude of this blip is a maximum when the transmitted beam points directly at the target, detailed examination of the blip may be made with a second cathode ray tube with increased brilliance known as a strobe, and can be moved to any desired position of the trace. As an alternative a single cathode ray tube may be used with two different timebases to display alternate traces The radial time base is synchronised with the rotating antenna of the radar system and the display appears as a circle with a rotating radial arm that leaves behind a bright spot representing the target, or series of targets as it rotates. The cathode ray tube display is effectively a plan view superimposed with a grid and topographical features, thus identifying the location of the target. This is called the PPI, Plan Position Indicator. Film cuts to show the incidence of the rotating antenna with the blip on the PPI, and the target, a ship under attack from an aircraft. “Controls” The use of the cathode ray tube is fundamental to radar systems as the film has demonstrated. The majority of radar controls are thus inherent in the cathode ray tube unit, brilliance of the spot, focus, two positioning controls X and Y, calibration and synchronisation.
  • Alternative Title:
  • Colour: B&W
  • Digitised:
  • Object_Number: AMY 230
  • Sound: Sound
  • Access Conditions:
  • Featured Period: 1939-1945
  • Production Date: 1943
  • Production Country: GB
  • Production Details: Air Ministry (Production sponsor) British Thompson Houston Research Laboratories ()
  • Personalities, Units and Organisations:
  • Keywords:
  • Physical Characteristics: Colour format: B&W Sound format: Sound
  • Technical Details: Format: 35mm Number of items/reels/tapes: 3 Footage: 1124ft
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  • Link to IWM Collections page:

    AMY 230

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