NEW TV TOWER MAY CAUSE DIFFICULTIES

Press, Volume CIV, Issue 30763, 29 May 1965, Page 1

NEW TV TOWER MAY CAUSE DIFFICULTIES

Because of the introduction this year of higher-powered television transmissions in some centres, including Christchurch, manufacturers have warned installation technicians that they can expect difficulties —chiefly “multi-path signals,” or “ghosting” as the phenomenon is commonly called. »

Increased reflection of signals from natural and man-made objects, resulting in double or multiple images on television screens, is predicted in technical bulletins sent out this week. Manufacturers say “ghosting” from hills, buildings, chimneys, powei’ pylons, bridges, and even trees may be aggravated and require expert adjustment.

One manufacturer has given a formula by which the offending “reflector” may be identified. It consists of measuring the interval between the main and “ghost” signals in microseconds and multiplying this figure by 300 to give a distance in metres. A search is then made for an object at this distance from the aerial which may be causing the “ghosting.” Trial And Error Those in the business say curing “ghost” images is still largely a matter of trial and error in orientation of the antenna. In some cases it may even be desirable to reject the direct signal and concentrate on the reflected signal, for example by turning the antenna vertically. With indoor aerials a change of only a foot or two may

make a considerable difference. “Pre-ghosting” or leading signals, which arrive ahead of the main one, may also arise. Some of these, one bulletin says, may be collected by the lead-in cable or by parts of the receiver itself-. Besides shortening unnecessarily long leads, the insertion of alternator networks is recommended. Because those in the trade are being advised that they may expect new problems, it seems that simple turning of aerials toward the new trans-

mitter on Sugar Loaf Hill (when it opens) may not be enough. “We could receive a plaster of calls from up to 5000 television owners all wanting adjustments the day the new tower is used,” said one representative of the trade. “Until it opens we don’t know what to expect; but I hope the public will be patient.”