A V/S Special transmitter is essentially a lantern, similar in general design to an ordinary V/S lantern, fitted with a screen which prevents the passage of almost all the visible light radiated from the source and allows only the short-wave infra-red radiation t? be transmitted. Light from the transmitter is visible, for short distances only, as a deep red glow; the infra-red radiation cannot be detected without the aid of a special V/S Special receiver. |
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A V/S Special receiver is an instrument that converts an image, formed by infra-red radiation received from the transmitter into a visible image. When a V/S Special transmitter is viewed by means of a V/S Special receiver, a spot of light is seen in a manner analogous to that in which light is.seen when a source of visible radiation is viewed by the unaided eye. |
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It is known that other countries have apparatus, similar to the V/S Special apparatus, in naval use and every effort should be made to detect and report enemy transmissions. Similarly, precautions must be taken when using transmitters on the assumption that the enemy has means of detection similar to our own. In general, therefore, the use of the transmitter, selected for a particular application, should be limited to the range and dispersion required. Special care must be taken in enemy waters. |
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Receivers. |
The term "V/S Special receivers" covers any apparatus (except television) capable of receiving infra-red radiation and transferring it to the eye as a visual image. |
Transmitters. |
V/S Special transmitters may be divided into two classes
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Trans-Receivers. |
These consist each of a transmitter and receiver, combined to form one unit. They are used in cases where the operation of both transmitter and receiver is required to be carried out by one operator. They are essential for use with "corner cube" reflectors. In this system, the operator transmits a beam which is picked up by a special reflector (known as a corner cube) and sent back to the operator. The system requires the receiver to be close to the source of transmission. |
It must be stressed that the performance obtained by any system of receivers and transmitters depends not only on the strength of the transmission but also on the sensitivity of the receiver. Since these vary under different conditions and, to a certain extent, from one instrument to another, it is essential that operators should know the individual performances of the instruments supplied to them. The following considerations affect the performance of V/S Special systems. (i) The accuracy of training of the transmitter. Transmissions are stronger in the centre of the beam and grow weaker towards the limits of dispersion. (ii) Atmospheric conditions and temperature. The transmission of infra-red is affected by fog in the same way as that of visible light. Also, the sensitivity of the receiver, and hence the greatest range of the system, is reduced at high temperatures. (iii) Condition of optical system and cleanliness of glass, screen, etc. (iv) Age of transmitter lamp. (v) Condition and endurance properties of transmitter battery. The performance of the battery will drop after it has been in use for some time. Since both transmitters and receivers are affected by high temperatures, special steps have been taken to provide for efficient operaticn in the Tropics. |