Closure of MT Eden VHF communications site

By Ian Walker ZL1BFB

The New Zealand Post Office had a communications centre on Mt Eden in Auckland, which provided communications to businesses and emergency services in and around the city.

This VHF radio centre was housed in two buildings near the top of Mt Eden, although not actually at the summit. No public access was permitted but there were all sorts of stories about what the technicians actually did inside the buildings. One of the two concrete huts was used for the transmitters and the other for the receivers, the roof of the latter being used as a lookout platform for visiting public. Siting of the buildings aided the electrical requirement for repeater separation usage, and each had its own power supplies and underground services. Access then was by the same steep narrow one way road which still winds round the side of the hill.

Passengers in the vehicle enjoyed the views but the driver had to keep a steady eye on the road for pedestrians as well as roaming cattle. There was normally ample parking for tourist cars and buses at the summit. The PO had a service driveway to the transmitter hut which kept their vehicles away from the general public, and meant equipment could be carried in and out without undue hindrance from public and also gave a little security.

It was an easy walk from either hut to the summit Obelisk and Cairn, which had a map showing points of interest about the Auckland isthmus and farther afield. Many group and scenic photos were taken by visitors to the area at this point. The main viewing platform was an even shorter walk to the roof of the VHF receiver building to the east. From here could be seen the two harbours, as well as the spread of the Auckland CBD and surrounding suburbs. Both the receiver and the transmitter huts were supplied with 100 foot masts to carry the many antennas. I have been able to obtain some photos of the inside of the transmitter station, and also of the antenna poles.

Inside transmitter building on Mt Eden, Auckland

Transmitter racks, holding mostly Collier & Beale 57 sets, PYE Cambridge and later Tait transmitting equipment and associated Deltec filters

The units seen here were mainly on the “A” and “B” bands of frequencies and the method of connecting the transmitters to the antennas can also be seen by the coaxial cables coming from the sets. From the transmitter set they went into a band pass filter then into an ‘Octopus’, (which I’m told was made by NZPO). From here the signal was passed into another “Octopus” (NZPO) with quarter wave stubs and then into a “Trombone” (another PO design), and up the heliax to the appropriate antenna on the 100ft mast.

The telephone cables were transferred in pairs to the receiver hut, and these pairs fed off to each piece of equipment.

The trolley table held the test generator and the tools for the job and a multi mains plug to power the portable equipment. A small footstool or short ladder was available for those who had to reach the high connections, or could be used as a seat.

Inside the transmitter building on Mt Eden, Auckland

The wall at the end of the transmitter racks had a panel where cables from the Post Office telephone exchange terminated.

Although air conditioning was not installed until later on the building was very comfortable on cold winter days, as the operating valve equipment kept the place quite warm and cosy. In summer, however, one had to leave the door open to get a cool airflow.

There was also a big diesel electrical generating plant at the transmitter hut which, when operating, became a great noise generator and vibration conditioner for the building. It was uncomfortable trying to monitor the channels when it was running, as I found out on many an occasion.

This was a 24-hour operation, and during the working day there was normally a technician on duty in case of a service breakdown or to make necessary changes to equipment as required

Some of the services supplied were to the Police, Fire and Ambulance Services, local councils, taxi and trucking companies, Auckland Radio, a telephone service to Great Barrier Island, and many others.

The heliax cables between the antennas and the main patch panel had their entry point also on the rear wall and were divided amongst the equipment as required by the various tuned coaxial cables and filters.

Radio mast on Mt Eden, Auckland

Timber bracing supporting the host of antennas most of which was to lead to a little cross modulation effect. This situation was mainly engineered out by having only certain radio channels on site.

The antennas on the masts were changed in design over time to give the best coverage and bandwidth for 50 Kc/s, the operational band width in those days. The VHF conical antennas were special brass rods welded into a conical shape. They were at the time a great antenna, any minor failure rate being caused by poor welded joints, whereas the dipole type antennas failed due to osmosis or cracking of the plastic covering allowing moisture to enter.

The poles and the buildings remained for many years until they were deemed aesthetically unacceptable and were removed from the Mt Eden skyline. The Post Office (later Telecom) negotiated the removal of the radio station and the transfer of equipment to Sky City.

The site at Mt Eden closed in 2000.

Although OSH requirements for increased safety standards provided more protection for riggers with scaffolding around the masts, memories of their skillful and sometimes daring feats still brings nostalgic admiration.

Test room at Mt Eden radio site, Auckland

This photo is of the early model test room which was modernised a few years later with better equipment, larger desk, and more work for the technical staff who manned it.