DIRECTORATE OF TELECOMMUNICATIONS
THE FIELD ORGANISATION
By: A N Holdstock
page 5 of 8


a. Faulty diagnosis, using a fool-proof indicator system, would be rare.

b. Faults such as complete loss of power supplies at a hill top site would be apparent if a number of tests proved negative.

c. Changing individual units is preferable to changing bays because the chance of two units of the same type failing together is less than the chance of a failure occurring in two bays at the same time. (The standby bay carries similar equipment to the working bay).

d. By checking all systems at frequent intervals or by checking systems in an area as soon as a fire alert occurs in that area, it is possible to rectify a fault before it becomes apparent as a result of an operational failure.

This method would then, in the case of main station equipment, become FIRST LINE SERVICING, to be followed by second and third line in the same way as with mobile equipment.

Systems Problems

The two major maintenance problems with which we are concerned are together responsible for more communications failures and complaints than all other faults put together.

Phase of Incoming and Outgoing Channels

This problem is applicable to multi-station schemes only. All sounds are produced by vibrations which can be passed on in the form of a pressure wave in the air.

Electrical replicas of these waves can be produced by using a device such as a microphone, and these electrical waveforms can be depicted as shown in diagrams I to 6

Figures 1, 2 and 3 for instance might illustrate the sounds made by a flute, and are waveforms composed of one frequency only and known as sine waves. Figures 4, 5 and 6 do not have their origin in any instrument but are complex waveforms in that they contain the basic frequencies of waveforms 1, 2 and 3 plus an infinite number of harmonics, or frequencies which are multiples of the basic or fundamental frequency.

The human voice produces sounds which have their origin in the vocal chords and are then modified or altered in form by various changes in the shape of the mouth, to produce letters, syllables, and words. The reason we can hear and understand different letters and syllables is because the waveform of a particular sound is always the same, and vastly different sounds such as the letter "S" and the letter "0" are very different in form whereas the letters "B" and "D" would be somewhat alike. If reproduced on a cathode ray tube and photographed they would, in form, lie somewhere between the waveforms illustrated in figures 1 - 3 and those shown in figures 4 - 6

It follows from this that if the waveform is distorted or altered in any way, then the result of feeding the changed waveform into a loudspeaker would be a different sound, probably not recognisable as the original letter or syllable.

Source: Home Office DOT Exhibition 1971 Papers

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