Himatangi Radio bearers

By Rex Johnson

Rex JohnsonThis page discusses the ‘bearer’ systems which connected Himatangi Radio Station to other land-based points of the New Zealand Post Office communications network, mainly for the purpose of providing speech and telegraph traffic to the station for onward transmission over HF radio circuits.

There were two key bearer systems for Himatangi Radio:

  • a VHF radio circuit to Wellington (“South VHF”)
  • a 5-channel VHF radio circuit to Irirangi Naval Base near Waiouru (“North VHF”)
VHF bearers at Himatangi Radio in the 1970s
The South VHF bearer was at the hut at the top left of the picture. North VHF was at the top right of the picture beyond the red-roofed farm building. Photo c1970s courtesy Rex Johnson. Click to enlarge

VHF Bearer (South VHF)

Installed during the initial construction phase of Himatangi Radio was a VHF bearer system to Wellington. The Wellington terminal was at Mt Albert (approximately in the row of hills just south of the Wellington zoo). There was a repeater site at Colonial Knob to the north (on the coastal range of hills above Tawa Flat) which allowed a clear radio path north up the coastline to Himatangi.

Two VHF (80 Mhz) rhombics were erected at Himatangi for the link, along with a purpose-built equipment building at the rear (west) of the property. In the 1970s this building was referred to as ‘South VHF’ because its traffic route was to the south of Himatangi. Traffic was cabled to the Himatangi Radio carrier room.

Marconi 48-channel VHF bearer equipment, c1970s
Marconi 48-channel VHF bearer equipment, c1970s. Photo: Rex Johnson

The radio equipment used was Marconi 48 Channel VHF operating at a frequency of around 80 MHz. According to an Information Note of February 1958 the service carried two 12-channel carrier groups. One of the groups brought traffic to Himatangi Radio and the other group was passed on to Palmerston North by landline to provide twelve toll circuits between there and Wellington. The NZPO had commonly used Marconi 48 channel equipment around New Zealand as it sought alternatives to running masses of wires on telephone poles between main centres.

5-Channel VHF Bearer (North VHF)

The North VHF building at Himatangi Radio, c1970s
The North VHF building at Himatangi Radio, c1970s. Photo: Rex Johnson

Also situated at the rear (west) of the station buildings was another smaller equipment building. This was the site of the ‘North VHF’ bearer system which used GEC equipment to provide five VHF radio channels northward to the Royal New Zealand Navy’s radio station at Irirangi near Waiouru.

Murray Smith checks the GEC link equipment at North VHF, c1970s
Murray Smith checks the GEC link equipment at North VHF, c1970s. Photo: Rex Johnson

GEC 5-Channel equipment also seemed to have been a standard platform used by the NZPO into the 1970s for smaller bearer circuits at other New Zealand locations. Apart from annual maintenance of the equipment, the North VHF system did not need much technical support. Traffic information was cabled via the Himatangi Radio carrier room to the Defence Communications Centre in Wellington.

Wellington – Palmerston North coaxial bearer

About 1962 the NZPO completed a major upgrade of telephone and telegraph circuits between Auckland and Wellington. This consisted of a coaxial cable bearer between Auckland and Hamilton, a microwave bearer system between Hamilton and Palmerston North, and another coaxial cable bearer between Palmerston North and Wellington. Joining these three separate systems provided the increased traffic services sought. The relevance for Himatangi Radio was that the southernmost coaxial cable passed by the station. In fact, an equipment building to service the cable was located just inside Himatangi Radio’s front gate.

Palmerston North - Wellington Coaxial Bearer brick building at Himatangi Radio gateway in the 1970s
Palmerston North – Wellington Coaxial Bearer brick building at Himatangi Radio gateway in the 1970s. Photo: Rex Johnson

It is unlikely that any coax cable carrier groups were used by Himatangi. However, it is likely that cable pairs wrapped around the coax cable were used for telephone circuits to Foxton and connections to Palmerston North.

One function of the Himatangi coax cable building was to house a SCUBA diver’s tank. The function of the tank and a combined air regulator was to feed a steady low pressure of dry air through the outer protective sheath of the coax cable so that the inside of the cable was pressurised. This meant that any tiny leaks in the cable would produce a steady flow of air outward, thus preventing any moisture from getting into the cable. A regular check by maintenance staff would show if compressed air was being used at an unusually high rate and if maintenance work was required.

Published October 2016