NEW TELEPHONE SYSTEM

Taranaki Daily News, 5 October 1929, Page 11

NEW TELEPHONE SYSTEM

CARRIER CURRENT IN HAWERA INSTALLATION FOR TOLL CALLS. GREAT ADVANTAGES OF METHOD! To the layman it seems almost incredible that three persons can bo in telephonic communication with three other persons, each in different centres and each using the same line at the same time. Further it is hard to realise that there can be a gap of t"O chains in that line, perhaps caused by a breakdown, and yet tho voice will jump the gap, connect with the othei end of the line and be perfectly audible hundreds of miles away. It is neverflie-: less a fact, and Hawera residents will this morning be able to converse with residents of Palmerston North and hear better than if they were speaking by plioile with friends in Hawera. This has bce'ri' brdugh't about by the installation of the most modern inveu-. tion iu telephony, the carrier ivave system, in the Hawera post office. For the last few days departmental engineers have been installing the apparatus and expect to complete their work this morniug* Tho system,' which was invented in America, was first tried in the United States about. five years ago. Shortly over a year ago” a' New Zealand engineer was sent to Australia to inspect the installation of ; tfic System in the Commonwealth and it Avias as a result of his investigation’that it'.was decided to instal it througlid.ut the Dominion. The work has gone''Ahead gradually and already Auckland has been connected with Hamilton, Hamilton , with Palmerston N'.rth and Phhnerstpn North with Napier and ifaiUrira. In tho South Island, Seddon, a ! srirall Marlborough town,; has been converted with Christchurch. After the, installation at Hawera the engineers' will go bn to. Wellington and instal; the plant there, thus completing the'’chain from Auckland to Christchurch. Eventually the system will operate throughout the Dominion. From Wellington a submarine cable crosses Cook Strait, runs down the east coast of the South Island and travels up the Awatere River to Seddon. The complete plant costs about £l6OO and does away with the necessity of erecting' a land line. Such a line from Hawera to Palmerston would cost about £6OOO. With the carrier system the maintenance cost is practically nil, whereas with a land line it is fairly heavy. . The machine is of simple construction, is portable and takes only a few days to instal. It stands on an iron base about 2ft by Ift and is 7ft high. The actual equipment is similar to that of a radio set, consisting of valves, transformers and condensers. By the installation of the apparatus in Hawera a direct connection with PalNmerstbn North is made,” said one of the engineers to a Daily News representative yesterday. “It does not involve the erection of'a new line, as the old line passing through Wanganui, can still be. Utilised. Using that line Hawera will be enabled to be in communication with Wanganui and Palmerston North simultaneously.” Ho stated that the system involved a high frequency carrier current between Palmerston North and Hawera. Ordinary speech frequency, ranged from 360 to 2700 cycles, while carrier frequency ranged from 4000.'td 16,000 cycles, a fact which would almost eliminate line interference. Speech, was amplified by valves in a manner similar to that of a radio set. The speech input at Hawera would be modulated (converted from ordinary speech frequency to carrier frequency), passed over the line at high frequency and demodulated at Palmerston North. The separation of ordinary speech from carrier speech was obtained by means of filters, whieh were pieces of electrical' apparatus having the properties of passing either high or low frequency. The low-pass ■ filter passed speech frequencies. ,anfl rejected carrier frequencies, while ,j.he high-pass filter did the opposite. The installation was-;..tested yesterday with satisfactory Jesuits.