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Appreciable developments in the design and application of ripple-control equipments have taken place during the past ten years. The paper reviews the progress made and indicates the modern requirements of such systems in view of their proved value to the supply authority and their anticipated widespread use. Basic requirements for a system of ripple control are described, followed by a method of network analysis for predetermining the ripple power required to give a desired signal strength, and for evaluating its degree of uniformity, on a known supply network. Limitations in the practical and economic application of series-injection methods for superimposing the signalling power on the supply system have led to the parallel-injection method being more usually adopted. The modern injection circuits described and methods of connecting them to the electricity supply networks show that appreciable improvements have been made in injection efficiency, with corresponding reductions in size of plant required. The need for ensuring that a ripple-control system should not be liable to mal-operation owing to Â¿spilloverÂ¿ signals is shown to be an important factor governing its principle of operation. The present trend of the art is to use a single ripple frequency as a Â¿carrierÂ¿ for each supply area, and to use some form of coding as the discriminating factor for affording separate control channels. The principle of various forms of coding suitable for ripple control, and receiving relays to suit such codes, are discussed. The economics of centralized ripple control for off-peak loads, and as a means of improving the domestic load factor, are reviewed.