Many Causes For T. V. Interference In Auckland

Press, Volume C, Issue 29421, 25 January 1961, Page 8

Many Causes For T. V. Interference In Auckland

“The Press- Special Service

AUCKLAND, Jan. 22. “Ham” radio owners in Auckland are unhappy about allegations by television viewers that their transmissions are to blame for interference with Channel 2 telecasts. “Television sets are subject to many forms of interference depending on the design of the receiver, its location, and the amount of signal it is receiving from the transmitter,” said Mr C. Betson, chairman of the Auckland Very High Frequency Group. “Unfortunately, Channel 2 is operating on low power from not the best of locations, and as a result practically all receivers are in areas of fringe reception, which means that not enough signal is received to overcome other scources of interference. “When Auckland gets its big tower and 100-kilowatt transmitter—in anything up to two years—9o per cent, of the interference on television will vanish.” Cars and Razors Among the sources of trouble were car ignition systems, sewing machine motors, electric drills and razors, flashing signs, street lamps, and household switches, lamps and wiring, said Mr Betson. Amateur radio transmitter interference formed only a small proportion of all interference. “When a receiver is near ah amateur radio transmitter the amateur can overload the station selector unit of the television receiver and cause

what is called a ‘blanketing effect.' This can remove both picture and sound, but the remedy is to install a highpass filter, which, if properly put in, should remove the trouble entirely. “When the amateur trans* mission interferes with television receivers not in the immediate vicinity of his station it is invariably the fault of the receiver. The design of the television set, the alignment of the intermediate frequencies for the picture channel, and the operation of the fine tuning control at the back of the station selector, plus the efficiency of the television antenna beam, can all be causes. Shared With Army* "Television uses a channel of seven megacycles—the equivalent of seven broadcast bands—for a signal. Some amateurs are operating on the 51 megacycle band, which is shared with the Army, and is half a television channel away from Channel 2. This separa* tion is more than adequate to avoid interference. “But no standards seem to exist for television receivers, and it is left to the individual firm's designer what precautions are taken against interference. “Quite a few receivers lack sufficient shielding to keep out interference, and at the same time to prevent radiation from the receiver itself, which can upset other television sets in the neighbourhood.” Post Office Check Mr Betson said that some amateur transmitters alleged to cause interference had been inspected by the Post Office, and were found to comply with all the present regulations. “But they can still cause interference if the television receivers are not properly designed,” he said. “The policy overseas is that it’s the manufacturer’s and purchaser’s responsibility to cut out interference—most of the .amateurs transmitting during television transmissions have been tested and are in the clear.”