TV DISRUPTION REMEDY SOON

Press, Volume CXII, Issue 33067, 7 November 1972, Page 16

TV DISRUPTION REMEDY SOON

The disruption of the television coverage of the election address by the Prime Minister (Mr Marshall) occurred on one of the few remaining stretches of the national television network which is not linked by microwave, says the New Zealand Broadcasting Corporation’s public relations manager (Mr R. E. Coury). He was replying to a correspondent, “Microwave engineer,” who, in a letter to the editor of “The Press,” wrote.—

“Why are we told that ‘ionospheric disturbances broke the link’ during last night’s political television link when it is a scientific fact that ionospheric disturbances were due to fading caused by multipath propagation — an atmospheric effect? The phenomenon has been adequately researched and it is common knowledge that short hops and frequency diversity remove this problem. I am appalled by the very poor engineering exhibited by the N.Z.B.C. in designing their links. It is only the indifferent she’ll-be-right attitude of many New Zealanders which makes it possible for the N.Z.B.C. falsely to proclaim the commercial viability of their microwave network. The N.Z.B.C. should have informed Mr Marshall of the risks involved in using their substandard link. In the circumstances Mr Marshall’s prudence in commencing his campaign from Whangarei is questioned. The circumstances were not beyond the N.Z.B.C.’s control, contrary to their claim.” Vulnerable section

Mr Coury said that “Microwave engineer” had assumed that the degradations to the television signal were because of the fading of a microwave signal at some point in the national circuit. “The breakdown, in fact, occurred over the section between the Wharete and Kaukau transmitting stations. This is one of the few remaining sections of the national television network that is not yet microwave, still relying on the Kaukau transmitter to pick up an ‘off-air’ picture from Wharete. “Microwave paths are where the television signals are carried between repeater stations on microwave ‘bearers.’ These signals are of very high quality and can be precisely directed between one station and another as

long as there is no obstruction. “Off-air, or rebroadcast, paths are where the normal television broadcasts of a main transmitter are received at the next repeater in the same manner as on the domestic television receiver and the off-air signal is the actual broadcast signal used by the general public.” “Relatively rare” The cause of the breakdown was a phenomenon related to ionospheric conditions, known as anomalous v.h.f. propagation over long distances, resulting in cochannel interference. “Under these relatively rare conditions, unwanted v.h.f. signals from other television transmitters on the same frequency are present and result in severe interference to the wanted signal,” he said. Microwave equipment scheduled for delivery next year would provide a microwave circuit between Wharete and Kaukau via the Wairarapa to replace this rebroadcast section of the linking system.

“Risk accepted” “Regarding the reference to the design of the microwave link systems, N.Z.B.C. engineers are fully aware of the factors relating to microwave fading, and of the techniques, such as frequency and space diversity, that are employed to elmininate the effects of such fading. The N.Z.B.C. already have certain microwave hops equipped for diversity operation. “We were well aware of the risk involved in originating Mr Marshall’s speech from Whangarei, but this was out of our control once we had advised the political parties against going away from main centres,” said Mr Coury. A