Skytower, A Light In The Centre Of Auckland
15 September 1996

Imagine a darkened room. Would you rather have the light in the centre or over to one side?

Most people would want the light in the middle of the room, where it would illuminate evenly. And that's the premise behind the $82 million construction of Auckland's latest and most prominent landmark.

Looming large in the view of almost every Aucklander, the Sky Tower is fast becoming the city's highest vantage point, and it is also quickly shaping up to be the major telecommunications tower for the region.

From its air conditioned equipment floors behind special low metallic, low interference glass to the tip of the mast, 331 metres above the ground, Sky Tower is designed to provide Auckland with the best broadcast and wireless telecommunications site possible.

"The site was chosen because it is the best place for a mast like this," says Sky City manager development, Bryce Morrin. The tower belongs to Sky City Ltd, the publicly listed company created early last year and Morrin is the client company's Representative in the project, which involves a long list of architects, engineers, consultants and construction specialists.

Although the tower will accommodate up to 800 visitors and staff, it will also host a variety of broadcast and telecommunications technologies. From sensitive line of site antenna and pie plate sized dishes mounted behind special low impedance glass to external three and a half metre microwave dishes and the gamut of broadcast aerials on the mast above, Sky Tower has been purpose built as a central telecommunications and broadcast mast.

"Behind the dark glass there are two air conditioned floors for delicate transmitters that need to be protected from the elements, plus another floor for the necessary electronics," says Morrin. "Above the rotating restaurant and the outdoor public viewing platform there are two external levels for mounting larger dishes. The mast is designed to accommodate a wide variety of transmission technologies, from VHF television to ultra-high frequency two way communications."

With the project counting down to completion, plans are being made to populate the tower with a variety of communications technologies that need a central location to be effective.

Despite its location and promise, not every potential customer is thrilled with the prospect.

"It's a pity it wasn't built twenty years ago," says TVNZ's distribution strategist Chris Lambourne.

He believes the tower may be too late to meet the city's immediate broadcast needs and says although it will improve television reception in Auckland, it is unrealistic to expect people to realign their television aerials or invest in more rooftop hardware without a compelling reason.

Located just across the road, Television New Zealand has its transmission equipment on a broadcast mast operated by BCL, at Waiatarua on the top of the Waitakere ranges. Like other prospective users TVNZ is currently 'in negotiation' with Sky City over the use of the tower.

While radio broadcasters have welcomed the tower with open arms, Lambourne says while Waiatarua may not be the best place to provide Auckland's television coverage, its height, 200 metres above that of the tower, serves the broadcaster's pledge to meet its USO-Universal Service Obligation. "It's not ideal, but it not only provides service to Auckland, it also feeds translators elsewhere in the country," he says.

"The tower will make it simpler for television broadcasters to provide live coverage of events," says Morrin. "It will eliminate the need to bounce signals all over town."

The tower will also reduce shadows and poor coverage areas caused by the city's volcanic landscape, especially if a broadcaster uses it in tandem with their existing equipment.

And for services like the Coastguard, the tower will be a godsend, offering the opportunity to eliminate poor reception in the inner harbour.

"We'll be good corporate citizens," says Morrin. "We'll make space available for peppercorn rentals for public services like Coastguard."

The location is also expected to appeal to other two-way communications users who rely on antiquated facilities on Mt Eden. The Auckland City Council has given marching orders on that site, effective once the tower is operational. "We have even been approached by Transit NZ , who believe it should be possible to mount remote cameras on the mast to monitor traffic flows around the city," says Morrin.

The mast also provides a platform for 'inter office' communications.

Expected to appeal to newer telecommunications providers, the tower is an alternative that is being looked at closely, according to Clear Communications spokesman Ian Parkes. "We already have leases with several landlords in the city, and this provides an argument in site renewal discussions."

While TVNZ is deliberating over its use of the tower, not all broadcasters share their reservations. It is understood that TV3 intends retaining its space on Waiatarua and relocating several of its translators to the tower to improve regional coverage.

"It will also be home for TV4," says Warren Harding, a broadcast specialist with the Tower's transmission consultants JDA - Johnson, Dick & Associates Ltd. The latest free to air station in Auckland will be operated by TV3 when it goes live later this year.

"It's a pity, because we were going to use those frequencies (TV4) to improve our coverage," says Lambourne.

JDA has been involved with the tower project since its inception. One of the first tasks JDA undertook was designing the earthing system for the structure. This required special techniques to integrate heavy duty copper earthing straps that run the height of the building into the reinforcing around the base of the tower to protect the tower and its equipment from lightning strikes.

The twelve meter diameter shaft houses three public lifts in a common shaft facing the sea, with a separate shaft housing a goods lift in the centre.

There are two stairwells running the height of the pod and a single stair from the bottom of the pod to the ground. It is possible to walk the stairs, in about twenty minutes. As well as the lifts and stairs, several large service ducts run the height of the building, with metal mesh floors every four meters. The tower has a fibre optic junction at its base and all internal construction is fire rated.

In the event of an evacuation of the public areas, the tower has three 'refuge' areas located at the lower levels of the pod, with a separate stairwell from the upper public areas. These floors are served by the goods lift and one of the passenger lifts and will provide a safety zone in the event of a fire in either the restaurant, kitchen or a machine room.

Because the Tower is the most prominent structure on the Auckland skyline, the designers have spared no expense to guard against natural interference that can generate short lived high voltage electrical spikes capable of igniting fibre glass and destroying electrical circuits in a flash.

To counter every possible contingency, butt welded 30mm steel rods are embedded in the concrete of the tower to catch side-strikes. A sophisticated Australian lightning system attracts energy to the tip of the tower and channels it to ground through a continuous length of ultra-low impendence triaxial cable.

"The System 3000 senses minute voltage fluctuations in the air and reacts instantly to attract a strike," says Enertec Services engineer Jon Davy. The company is the local representative for the Tasmanian based designers Lightning Protection International. "As the voltage rises to indicate an imminent strike, the Dynasphere on the mast-tip actually generates upward leaders to attract the strike and protect nearby antenna."

As an additional protection against uninvited electrical interference, all mains power circuits in the tower are also protected using a three step process that progressively minimises surge voltages that can be caused by lightning or even nearby electrical activity.

"Unless they are checked, voltage fluctuations cause subtle damage to delicate electronics," says Connector Systems automation interface expert Allan Schischka. "With lightning, several thousand volts in the power supply or data leads of a computer are by no means exceptional."

As well as providing protection for digital equipment, the TRABTECH-Transient Absorbtion Technology- from European industrial equipment supplier Phoenix Contact, safeguards the Honeywell analog control circuits required for the building's several air conditioning systems.

This technology is designed to provide progressive protection from currents as high as 60 kA and several hundred protective devices are in place throughout the tower's electrical circuits.

"We believe we have all the bases covered," says Morrin. "The tower is designed to last 100 years, and a lot can happen in that time."

Author: Ian Miller