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Hokitika Guardian, 27 December 1928, Page 2

Substantial savings in telephone extension costs and clearer conversation over trunk lines are the .outstanding merits claimed for the carrier system of telephony now being experimented with by the Post and Telegraph Department (states the New Zealand Herald). The tests are being made on the the service between Auckland and Hamilton, and as soon as the “0.k.” is given, the system will be brought into public use and extonded on other lines in tbo Dominion. The cost of a new telepliono lino between Auckland and Hamilton of tho type required for heavy traffic is estimated at £BOOO. Tho carrier system is designed to placo all the extra traffic on existing lines at a cost of £I3OO and to do away with tho necessity of adding to their number. Transforming apparatus is installed in the toll exchanges at the terminal points on tho system. The mechanism makes use of valves to pitch the sound vibrations caused by the subscriber’s voice up to high wave, giving a howling note which cannot bo recognised as the human voice or he understood until it passes through the companion plant 'at tho other end. Without a transformer it is impossible to tap a line being so used. An essential to tlie successful use of tbo carrier wave is the harmonising of the transforming mechanism at the terminals. To whatever height the sound waves are pitched at the point of despatch they must be lowered to exactly the same level at the other end.