NTA takes Black Mountain Off air to Install VHF & UHF Digital TV

Canberra - ABC-TV and Ten Capital's VHF TV signals will be off air in the early hours of Tuesday (14/7/98) morning to allow the installation of a Channel 12 combiner. Channel 12 and 29 will be used for testing Digital Television in the Canberra area. The combiner will allow channels 7, 9 and 12 to be transmitted from the existing VHF antenna system on the tower. The Transmitter has been specially produced by Itelco for the trial and is rated at 2.5 kW average power (digital). It is fed from an Itelco DVB-T COFDM modulator which is incorporated into the transmitter unit.

The National Transmission Agency are installing the equipment on Black Mountain Tower as part of a test program to determine how their existing infrastructure can be used for both Analogue and Digital transmission.

On Thursday (23/7/98) the UHF TV transmissions in the Canberra area will be off air to allow the installation of the UHF channel 29 combiner. This will see the operation of Channels 28, 29, 31 and 34 into the same antenna system. The NTA is using an ITIS DVB-T COFDM modulator feeding a converted NEC PAL 5 kW UHF transmitter and combiners supplied by RFS Australia.

Steve Farrugia outlined the NTA digital trial in a paper to the February 1998 ABA planning conference. This paper is also on this site.

Trial Background

The National Transmission Agency (NTA) has been engaged in trials of the new digital technology for radio and television transmissions for about two years, focussing until now on radio.

As with the continuing digital radio trials, the forthcoming digital TV transmission trials in Canberra will allow the NTA to test equipment configurations for possible use in the nationwide transmission network controlled by the Agency on behalf of the Commonwealth, and will assist staff to become familiar with the special requirements of this new transmission technology.

Evaluating different equipment configurations will facilitate planning of the new digital services and allow the NTA to estimate the likely costs of the new technology when applied across the entire network, one of the biggest in the world.

Television trials

An important reason for the digital TV transmission trials in Canberra is the need to determine the extent to which existing infrastructure can be used to support both the existing analogue and the new digital transmissions. The trials will also allow planners to compare digital signal coverage with coverage predicted using theoretical planning tools.

The trial broadcasts, scheduled to begin in mid to late July, will centre on Black Mountain as do the five existing TV services-the ABC, SBS, WIN, Prime and Capital.

The NTA will conduct the trials on both VHF and UHF channels with VHF 12 and UHF 29 being used. Test material will be transmitted in digital format to special receivers used in conjunction with TV monitors. Householders will be unable to view the test material because digital TV receivers are not yet available in Australia.

Agency staff will investigate the strength of the digital signal at various locations in the service area and assess the quality of reception.

The NTA has bought a 5 kW UHF transmitter for the digital TV transmission trials and has been loaned a 2 kW VHF transmitter by its manufacturer.

Radio trials

Trials of digital radio transmissions have been under way in Canberra for more than a year; before that, similar trials were held in Sydney. Recently the NTA commissioned a new site at Bywong Hill off the Federal Highway outside Canberra. Equipment at this site is linked with the Black Mountain Tower and a facility at Tuggeranong Hill, as a part of a Single Frequency Network (SFN) for the digital radio trials.

In an SFN, several radio signals-each carrying the same program material-can be broadcast on the same frequency from different nearby locations, but without causing interference, as would be the case were the present analogue system used. This has signal coverage and reception advantages.

Signals for the digital radio trials are being broadcast on 1.4876 GHz in the radiofrequency spectrum's L Band.The digital radio program material cannot be heard by the general public because existing domestic radio receivers cannot reproduce it.

14 July 1998

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