Radio Section, part 10: 1965-1987

By Chris Underwood

The next three pages on Radio Section cover quite a time span so will be more of an overview touching lightly on the numerous activities undertaken by topic.

Trunkline Rollout Continued

Wrights Hill, 2018
Wrights Hill in 2018
The rollout of new microwave systems continued apace including an overlay of the Palmerston North–Wellington coaxial cable link providing extra circuits and diversity.

The Wellington end was located in a new purpose-built station on Wrights Hill, near the old WW2 gun emplacements.

Although this work was now largely undertaken by the districts, most of the planning and purchasing of equipment was undertaken by Radio Section.

Chris Underwood (left) and Dave Burger checking the Lenkurt 776 microwave bay at Wrights Hill in 1965
Chris Underwood (left) and Dave Burger checking the Lenkurt 776 microwave bay at
Wrights Hill in 1965. Photo: NZPO

Microwave system training was now undertaken by Hamilton Radio Depot in conjunction with Lenkurt module repair.

More systems continued to be installed around the country and, in 1982, a very large 1800-channel Fujitsu 1+1 analogue hot standby system was installed between Wellington and Christchurch. It was extended to a 2+1 system around 1985.

Cashmere microwave station, the Christchurch end of the 1800-channel system
Cashmere microwave station, the Christchurch end of the 1800-channel system.
Photo courtesy Kevin Heyward

A training school for this equipment was set up in Christchurch and run by senior technicians on secondment from the Christchurch Radio Depot.

As there was no room at the Radio Depot for this school, accommodation was leased at the University of Canterbury’s Ilam campus. 

Training facility for the 1800-channel system in Christchurch
Training facility for the 1800-channel system in Christchurch. Photo courtesy Kevin Heyward

Many microwave stations were built on high or exposed sites. Damage from extreme wind or ice falling from higher up a tower onto dishes was a constant problem despite ice shields being fitted at known bad sites.

A microwave dish, damaged by ice
A microwave dish, damaged by ice

To reduce outages from this cause, restoration trailers were kept. Fitted with a spare dish and lengths of elliptical waveguide, these could be rapidly deployed and the dish mounted temporarily on the tower and fed by the waveguide until permanent repairs to the damaged dish were made or a replacement obtained.

microwave restoration trailer
A microwave restoration trailer.

To meet ever-increasing demand a new system using NEC digital microwave technology was designed and built. This was a major change in technology.

Tower for new digital microwave station being built in Ashley Forest, north of Christchurch
Tower for new digital microwave station being built in Ashley Forest, north of Christchurch.
Photo courtesy Kevin Heyward
Left: Digital microwave station near Palmerston North. Right: Racks of DMR equipment.
Left: Digital microwave station near Palmerston North. Right: Racks of DMR equipment.
Photos courtesy Kevin Heyward

Land mobile

Land mobile stations were being built as required all over New Zealand. The technology was being rapidly developed.

Chris Underwood at Wrights Hill transmitting station c1965
Chris Underwood at Wrights Hill transmitting station c1965. Photo: NZPO

By the mid 1960s the standard base station sets were the PYE 6001 transmitter and receiver units made in the UK, and the more numerous PYE 6201 sets manufactured by PYE in New Zealand. There were also a few Tait sets in use.

These were all valve sets and larger stations such as Wrights Hill transmitting hut got very hot, melting the wax impregnation out of the transformers of sets mounted near the top of the racks. Heat diverter panels had to be installed between transmitters mounted in a rack. This improved things considerably but although the transmitter station was a nice place to work in winter, it was somewhat hot in summer. The separate receiving hut at Wrights Hill was also warm but nothing like the transmitter hut.

PYE Cambridge with AC supply, for trigger base use
PYE Cambridge with AC supply, for trigger base use
Mobile sets for installation into vehicles improved rapidly. When I started at the Wellington Radio Depot in the mid 1960s, some of our vehicles used Collier & Beale 10L sets. Although quite a good set, they were heavy and took up a lot of room – and if you forgot to turn them off when you turned the engine off, inevitably the battery was flat when you came back ten minutes later. The introduction of the partially transistorised PYE Cambridge was a huge advance.

Normally, NZPO Land mobile stations were line-controlled but, where this was not possible, a mobile was used to access the repeater station. These mobiles were normally fitted with an AC power supply but in an emergency could be operated from a 12 Volt battery.

After the success of the Cambridge, PYE introduced a new base station receiver based on the receiver in the Cambridge.

PYE transistorised receiver
PYE transistorised receiver

The land mobile service started with 50kHz channel spacing in the B Band (roughly 100MHz). When more channels were required, channel spacing was reduced to 25kHz in the A band (roughly 80MHz) and the B Band, with a few E Band (roughly 150MHz) channels.

With the advent of FM broadcasting, there was a need to compress the channel spacing further, to 12.5kHz as the main land mobile services band (the B Band) was cut in half and the bottom half assigned to broadcasting.

New equipment with a much higher specification was required. GEC, which had just taken over Collier & Beale, produced the first 12.5kHz sets. These were followed by Tait-manufactured sets and later by the AWA NZ factory produced sets. These sets were very much smaller and multiple transmitters or receivers could be fitted in a standard shelf.

AWA 12.5kHz channel spacing equipment
AWA 12.5kHz channel spacing equipment

AWA land mobile equipment
AWA land mobile equipment.

AWA Teleradio
AWA Teleradio
New mobile and portable sets were required and these were produced by companies such as AWA and Tait. The Tait Miniphone became the defacto industry standard and outsold everything else, including the AWA Teleradio.

In major stations, traditional methods of connecting sets to common antennas using cavity filters and “porcupines” were no longer adequate and new techniques using combline filters for receivers and circulators for transmitters had to be developed.

These were designed in Radio Section’s fourth floor development workshop into formats suitable for mass production by New Zealand-owned and operated companies based in Tawa, near Wellington. One of the companies was Deltec and I forget the name of the others. This was probably the height of radio manufacturing in New Zealand, and today of all these companies only one remains.

All photos courtesy Chris Underwood (except where noted).


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