DIRECTORATE OF TELECOMMUNICATIONS
THE FIELD ORGANISATION
By: A N Holdstock
page 7 of 8


Stability of Mute Operation on Main Receivers

Automatic gain control - the means by which receiver output is kept constant with varying input - has been in universal use for many years. One of the unfortunate effects of this system is that when no signal is being received a great amount of noise is usually present.

Mute circuits were developed so that operators were not constantly forced to listen to this noise and so that signals were fed through to the operator only when the signal to noise ratio was good enough to make signals readable. Developments to receivers - in which the Directorate has played a part - have made it possible for signal levels of from 0.5 to 1 micro-volt to be readable above noise level, and it is natural that this technical accomplishment should be used in order to extend scheme cover from around 80/85% to almost 100%. It is obvious that reliable communications can only be achieved if the point at which the mute operates can be maintained at a stable level between 0.5 to 2 microvolts depending on the scheme end site.

Before operational equipment can be set up to give a particular performance, the test equipment used for the setting-up procedure must be stabilised at an even better level of performance. To this end the Directorate has recently set up a special test equipment maintenance and calibration centre at Weyhill near Andover. Very special calibration equipment has been installed, but even so the measurement and stabilisation of a millionth of a volt at a frequency of 100 million cycles per second is extremely difficult to achieve, even in a well equipped laboratory.

From this it follows that if special laboratory equipment cannot cope with the problem, even less can operational equipment be so stabilised.

This problem is being tackled by the Field Organisation of the Directorate, and it may be that a new technical approach is needed in order to ensure that worthwhile signals are not excluded by unreliable mute operation. In fact this problem is a good example of the way in which automatic gain control and mute operation, both worthwhile technical developments have assisted the operator but at the same time have contributed to system unreliability.

Although new uses for electronics in the field of communications are constantly being sought, and new control systems built, the basic need for system reliability is often not met. It is the job of the Field Organisation to ensure that maintenance is of the highest possible order, and to look continually for new methods, which will enable basic communications systems to give a more reliable service to the user. Force Communications Officers have done a great deal to improve communications between the maintenance organisation and the force, and it is to be hoped that with suitable training they will be able to play a fuller part in the vital work of maintenance.

Mr Holdstock joined the Directorate of Telecommunications in 1948 after Radar service in the RAF. He served in a number of depots and moved to headquarters in 1969 as a Senior Wireless Engineer in the Field Services section with responsibilities for installation, maintenance and the provision of special communications.

Source: Home Office DOT Exhibition 1971 Papers

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