New Zealand’s World War 2 ZC1 transceiver

4 versions of the ZC1 radio transceiver
The four main versions of the ZC1: Original Mk-1 top left, Mk-1 Type 2 top right, Mk-1 Type 3 bottom left and Mk-2 bottom right. Photo: C Underwood

By Chris Underwood ZL2CU

With the outbreak of War in 1939, authorities in New Zealand gave urgent consideration to the training and arming of the troops that would be sent overseas to help the British war effort. Equipment of all types was in short supply, including field radios. The Ministry of Supply surveyed New Zealand industry to determine what could realistically be manufactured locally under wartime conditions. The Ministry identified a total of six manufacturers of domestic radios, including a smaller number capable of manufacturing a wide range of radio equipment including high-power transmitters.

After much debate it was decided that New Zealand industries had the capacity to design and/or manufacture a range of special purpose radio equipment including a field radio, to be known as the ZC1. There was dissatisfaction with the reliability and range of the few existing field radios held by the army. These were generally considered to be barely adequate for training purposes. The new radio had to be much better and suitable for both mobile and field base operation.

A Radio Equipment Supply Committee had been set up with representatives from the Army, Industry, Ministry of Supply and the Post Office to oversee the specification, design, procurement of components and the manufacture of all new radio equipment. This committee reported in April 1942 that sufficient materials were now available for the manufacture of 750 sets of the 1000 ZC1 Mk I sets approved. Considerable difficulty was being experienced in obtaining certain components, especially meters. Difficulty was also being experienced in retaining skilled technical staff. The ongoing delay in commencing manufacture was causing the Draft Board to lose patience and it was becoming ever more difficult to convince it not to draft the radio technicians and skilled assembly workers required for the manufacture and testing of the new field radio.

Supply problems were only improved in late 1943 after samples of the ZC1 Mk I were tested by the Canadian Signal Engineering Establishment. Such independent testing was a requirement under the provisions of Lend Lease and the Canadians provided copies of their report to the American and English authorities controlling war materials supply. The report compared the ZC1 with a laboratory No. 19 set (Canadian) and indicated that, overall, the ZC1 was superior. The Canadian report particularly noted the following in order of importance.

The ZC1 Mk I gave better:

  • Range, both transmit and receive under normal and abnormal conditions.
  • Decided saving in primary power due to low battery drain.
  • Ease of operation in the field by even inexperienced operators, simplicity of dials and operating knobs on front panel.
  • Accessibility, in as much as servicing and replacement in the field was concerned.
  • Capability of being able to trouble-shoot speedily and easily, due to separate send and receive circuits and increased space for assemblies.
  • Flexibility as to type of aerial which may be used with sets.
  • Simplicity of netting procedure, and tuning, indicated by a definite dip in plate circuit.
  • Compact and lightweight (approximately half the weight of the No. 19) and comparatively easy to install in any vehicle.
  • Does not require an extensive installation kit.

Records indicate that after the Canadian report was circulated the American Pacific forces showed interest in acquiring a large number of ZC1 Mk IIs for their own use. Rather than outright purchase, completed sets were to be swapped for essential components required for the manufacture of the sets. Although a small number of sets seemed to have been supplied, no major orders eventuated.

Initial plans called for up to 30,000 ZC1s to be manufactured, including an order of 15,000 expected from Eastern Command. However, by the time production commenced, the rapid Japanese advance had already captured much of the area these sets would have gone to and the order never eventuated. Thus, in practice, only about half the proposed production number was ever built. During early production runs, each individual ZC1 took 60 man-hours to construct. Initial production was 20 sets per week, with a production goal of 2000 sets per month at peak production. It is not clear if this rate was ever achieved. Delivery of the first batch of five hundred ZC1 Mk Is was planned for December 1942.

ZC1 Mk-I Type 3
ZC1 Mk-I Type 3. Photo: C Underwood

Design

Design of the ZC1 Mk I is generally credited to Percy Collier and Bill Fever of Collier & Beale, a Wellington-based radio design and manufacturing company. It was, as far as possible, designed around components readily available at the time, largely those used in the manufacture of domestic radios.

Specifications

The ZC1 Mk1 is a 2- 6MHz, single band, CW, MCW and phone-capable transceiver, suitable for vehicle installation (jeep or radio truck) and/or field base operation.

The receiver uses a 6U7G RF stage, 6K8G mixer, 6U7G IF, 6Q7G detector and 1st audio stage, 6U7G output and 6U7G BFO.

The transmitter uses a 6U7G master oscillator, 6U7G buffer, 6V6GT PA, 6V6GT modulator and 6U7G modulation amplifier.

The power supply uses a non-synchronous vibrator with two 6X5GT rectifiers in conjunction with a tapped transformer permitting switchable HT voltages to provide two different RF power outputs. Its power requirements are 12 volts at 4-6 amps, depending on mode of operation. In transmit mode, a maximum of 2.75 watts RF output is achievable in standard configuration.

Using the supplied 34-foot rod field base antenna and associated counterpoise earth, the transmission range is typically 25-34 miles over rolling country. Use of more efficient aerials and sky-wave working permit much greater distances to be worked. The top sections of the antenna were suitable for mobile use over shorter ranges.

At least three production versions of the Mk I are known.

  1. The first version, produced in small numbers, was fitted with an aerial current meter. IF transformers with fixed cores and variable capacitors were used.
  2. The second version, also produced in small numbers, used the same IF transformers but had a plate with a watch holder fitted in place of the aerial current meter.
  3. The third and most numerous version used different IF transformers with fixed capacitance and variable cores. The watch holder is fitted directly to the front panel without the need for a plate.

Note: Serial numbers of sets are deliberately not in sequence, to disguise build numbers, hence providing little clue as to date of manufacture or actual numbers built.

Companion RF Amplifier ZA1 Mk I & II

The ZC1 had a matching RF power amplifier, model ZA1, for longer-range coverage.

The ZA1 Mk 1 was housed in a wooden case similar in appearance to, but much smaller than, the metal case of the ZC1. Two parallel 807s operating in class C were used as an RF amplifier producing 50 watts output. This unit was intended for CW use only.

A second version, the ZA1 Mk II, differed in that the parallel 807s were modulated by a second pair of 807s fed from a 6V6 phase inverter and a 6U7 microphone preamplifier. The ZA1 Mk II unit was a much larger and heavier unit, housed in a modified metal ZC1 Mk 1 case. For this unit, the ZC1 acted only as an RF driver and keying or modulation are achieved via the ZA1 Mk II amplifier.

Neither mark of the ZA1 was produced in quantity. Official records indicate it is likely that only 12 production ZA1 Mk IIs were ever made. They were ordered and delivered in mid 1943.

Manufacture

Although the first trial batch of ZC1 Mk I units was manufactured by Collier & Beale, all subsequent production was undertaken by Radio Corporation of Wellington and Radio (1936) Ltd of Auckland. Many subassemblies and components were manufactured by other companies. Key components such as meters, valves and the main tuning capacitors were all of Australian, American or English manufacture.

Shortage of these components was to plague production until the later part of the war when American “Lend Lease” components became available. Official NZ war records show considerable frustration with shipping problems with large quantities of urgently needed, and already paid for, components being held up for many months on the wharves in the USA while officials argued over their shipping priority.

In all, approximately 5000 ZC1 Mk I sets were made. Even before manufacture of the Mk I began, design and production of the Mk II was already being planned.

ZC1 Mk II
ZC1 Mk II. Photo: C Underwood

ZC1 Mk II

Experience with the Mk I in the Pacific proved the basic soundness of the design but also highlighted the need for improved tropicalisation of the sets. The Mk II was a development of the Mk I and its design is generally attributed to RJ Orbell of Radio (1936) Ltd.

The significant differences between the two are as follows:

  • The Mk II is dual-band, having an LF band of 2-4 MHz and an HF band of 4-8 MHz.
  • A synchronous vibrator was used dispensing with the need for the two 6X5 rectifiers.
  • The switchable HT voltage feature was dispensed with.
  • Much improved tropicalisation of components and sealing of sets.

The ZC1 Mk II completed its service life without further change. A small number were manufactured with “flying rubber leads” for use with the combined microphone/headset as used by the No. 19 and No. 62 sets.

Official records show that the Mk II was originally planned to have a UHF transceiver included in the design. However, unlike the No. 19 set, this was to be housed in a separate case with its own power supply and capable of independent use. This idea was not followed up, although prototype UHF modules for this project were designed and constructed as a joint effort between Collier & Beale and the NZ Post Office Radio Section.

During 1943 consideration was given to producing the Mk II as an FM-capable set, following the lead of developments in the USA. A small number of ZC1 Mk 1 sets were modified by the DSIR to permit AM or FM modulation to allow comparative field tests of the different modes under real operating conditions.

FM operation was proven to have a number of advantages over AM during severe interference. However, despite this, the decision to continue producing the Mk II as an AM-only set was made on the grounds of cost and expediency. It was calculated that production of the Mk II as an FM set would have set back production of the Mk II by at least six months and significantly increased the cost. It seems probable that, had the war gone on, such a set, or a derivative, would have been produced as the ZC1 Mk III.

Radio Ltd and Radio Corporation undertook production of the ZC1 Mk II with sub-assemblies being provided by other manufacturers. Official records indicate that orders were placed for 10,000 ZC1 Mk II sets, but only a little over 9500 of these had been manufactured when production stopped. One document attributed to Eastern Command put the total production of ZC1s at 14,601 sets.

War Service

The first issue of the ZC1 Mk I was in the Pacific at Guadalcanal, and it saw active service for the first time when NZ troops landed at Vella Lavella at 8am on 18 September 1943. Official records indicate that it performed well in the dense and wet jungle, outperforming many other types in use at the time.

The Mk I also saw service on Stirling Island where, once again, good results were achieved. The NZ 3rd Division 2nd NZEF records show that they used the ZC1 in conjunction with the American 48 Set with good results. However given the relatively small overlap of the frequency ranges of the two sets, the choice of working frequencies must have been limited.

This Pacific campaign was the only recorded active service seen by the ZC1. Although large numbers of the Mk II version were sent to the Middle East and Europe, they arrived too late to see active service in WW2. However, a number saw service on the home front in NZ during the last months of the war.

The ZC1 Mk II also saw service with the NZ occupation force (J Force) in Japan after WW2. The sets used by J Force were among the last to be manufactured, and a special run using “flying leads”, as used in the No. 19 Set, was produced in the hope of increased inter-changeability with the No. 19 Set which other Commonwealth Forces were using.

Civilian use

In late 1944, a large consignment of ZC1 Mk IIs was set to Egypt, but arrived too late to be issued. Many of these sets appear to have been eventually issued to post war Greek, French, Belgian, Turkish and Egyptian armed forces. Numbers of these sets remained in service with these forces until the late 1950s early 1960s.

Also, a significant number of sets from this shipment were sent to the UK, where most were eventually disposed of as war surplus.

In New Zealand, the ZC1 Mk II continued in service with the Territorial Reserve forces until the mid 1960s. They were also issued to many Government agencies and departments including the Ministry of Transport, Civil Defense and the NZ Post Office.

The Amateur Radio Emergency Corps (AREC) also received a significant number of sets and many were also disposed of as Army surplus. During the 1950s and 60s many NZ Amateur radio operators “cut their teeth” using ZC1s on 80 metres. Their owners extensively modified many of these ZC1s and numerous articles appeared in Break In during this period describing improvements that could be made.

Collier & Beale produced a modification kit for the Mk II to make the set more suitable for small ships maritime use, and large numbers of ZC1s were used in this service. The LF receiver section was changed to the AM broadcast band and the HF TX and RX sections to the marine band.

Common modifications included xtal control for fixed channel use, used by the MOT for car-to-car communication for their traffic control cars, the Post Office for point-to-point services and various organisations and individuals for maritime use. Changes to improve RF power out and modulation depth were also common.

Cost of the Wireless Set No. ZC1 Project

In documents published in the mid 1960s on the New Zealand War Economy, reference is made to the production of the ZC1. In papers corrected and supplemented by Mr R Slade, former Controller of Radio Production, it is noted that sets and spares sufficient for 15,000 complete stations were ordered to the value of just over £3 million. These documents also record that, of the 15,000 sets ordered, only 14,601 were delivered before production was stopped.

These figures suggest that, on average, each individual set cost in the region of $NZ40,000.00 in 2009 values. The average expected life of a set under wartime conditions was 6-18 months.

Production involved a total of 56 factories making parts or assemblies and the two factories where production sets were assembled. At peak production, during 1943-1944, 900 individuals were involved in the ZC1’s manufacture.

Acknowledgments

Thanks to Roy Symon of SPAM for his generous assistance with information.
Thanks to Fred Johnson, Bill Heinz and Reg Motion for their support and guidance.

Learn more about the ZC1

ZC1 Radio Club