TRUNK TELEPHONES

Otago Daily Times, Issue 23830, 9 June 1939, Page 2

TRUNK TELEPHONES

HOW EFFICIENCY IS MAINTAINED TESTS WITHOUT SPEECH Periodically throughout the day the long-distance telephone circuits which link New Zealand’s towns so effectively are tested in order to maintain their efficiency at the dear-speech point. The modern method is far different from that of the day when there were no “carrier” circuits. Once it was a case of shouting “Can you hear me?” and a complaint if the conversation could not be maintained by the exercise of considerable lung power. Modern tests on the carrier circuits do not involve speaking. Expert mechanics are able to check speech efficiency and make adjustments compensating for variations due to atmospheric conditions which may interfere with the constant flow of revenue-pro-ducing speech. They employ a method of electrical measurement of sent and received current at the telephone frequencies, and this is done periodically throughout the day. On the most important circuits carrying the longest trunk-line business the Post Office engineers have installed ingenious apparatus which constantly attends to variations in the circuit, changes being made automatically which compensate for losses due to electrical leakage generally caused by bad weather conditions. Many radio listeners are familiar with the automatic volume control operated on their sets, and they know from experience how well this system deals with great variations in signal strength. The Post Office apparatus bears some resemblance to the volume control on a radio set. although it is much more elaborate and costly.