RF - Shortwave
This page continues our review of the development of radio services in New Zealand. Here we focus on 'shortwave' radio frequencies (RF), which enabled the follow-on services from longwave radio. A key development was the concept of 'beam radio' which directly affected much of the equipment types selected to replace longwave services at NZPO coast stations. Shortwave services also became the main medium for communication to regional remote land-based sites.
Amateur Radio - Pushed into the Wasteland
Longwave transmission was considered the only usable part of the frequency spectrum and those low frequencies were controlled as the 'official' domain of government and commercial radio services. Consequently, in 1912 the US Senate restricted American amateur radio operations to the supposedly useless frequencies above 1.5 MHz (200 metre wavelength or shorter).
Much experimenting and many advances in radio communication can be attributed to individuals and the amateur radio community. Amateur operations were closed down during the war years, but experimenting in their 'radio wasteland' recommenced when that restriction was lifted. In 1921 American amateurs challenged their UK counterparts to receive radio contact from them and many signals were soon heard. At the end of 1922 a UK signal was heard in the US and by the end of 1923 a transatlantic two-way contact had been made. By 1924 New Zealand amateurs had made contacts with their counterparts in South America, North America and Britain.
In 1923 the Marconi Company was experimenting with low power shortwave technology, however they did not yet have a confirmed commercial product. In July 1922 when the British government announced it would build the longwave station at Rugby, they also added, almost begrudgingly, that they would build some 'beam stations' to communicate with those Dominions which chose to use the new technology. In August 1924 a new British government confirmed this plan, identifying beam stations to communicate with Canada, South Africa, India and Australia. So what enabled this 'beam station' concept?
Wavelength and Frequency
Radio frequency and wavelength are directly related. Low frequencies have long wavelengths while high frequencies have short wavelengths. Also, the most efficient transmission and reception of radio signals was found to be through using aerials that were 'resonant' at one half of the wavelength in use. This meant that aerials used for shortwave circuits could be smaller than aerials used for longwave circuits and be just as efficient. Consequently, aerial support towers could be shorter and easier to maintain. There were definite aerial cost efficiencies to be had in using shortwave technology.
Even in early longwave aerial development it had been found that a good 'ground plane' improved signals, even if that reason was unclear. For instance, while Telefunken's 400 foot longwave towers supported lots of aerial wires at great height, they also included many wires at or just above ground level spreading out radially from each tower. When experimenting with shortwave aerials it was found that the earth itself could form this 'ground plane' and was particularly effective where ground was damp and a good conductor. Then came the understanding that the ground plane was acting as a mirror and was reflecting radio signals back up to the aerial wires. Aerial design could now factor in this 'mirror' effect for improved signal strength.
Not only was the earth a reflective mirror at radio frequencies, but it was found that for shortwave signals the earth's upper atmosphere (ionosphere) could also act as a mirror. At night there was a layer at high altitude that reflected and during the day the suns rays created additional reflective layers closer to the earth. This opened up the concept of having shortwave signals 'hop' over a distance by bouncing them off the ionosphere before coming back to earth. Further, there could be 'multi-hop' signal paths where radio waves repeatedly bounced between the ionosphere and earth. It was also found that stations in between the earth's 'hop' points would not hear a signal even though stations further away could receive strong signals. This effect was also known as 'skip' as in the 'skip distance' of a radio signal.
Hop distance is affected by two main factors, the frequency of the signal and the time of day which controls which ionosphere layers are present. An additional factor is whether the sun's energy is different than normal, either through sun spot emissions or during auroral activity. For stations working to the other side of the earth's globe there were advantages if a radio signal could be sent on the night-time side of the world. The ionosphere was likely to be more stable and at a higher altitude than on the day side, resulting in fewer hops and clearer signals at the receiving end of the circuit. But how could a choice be made which way to send a signal?
Beam Wireless Concept
A big advantage of using high frequencies and short wavelengths is the flexibility available to design aerials for particular uses. Designs were found which would focus transmitter energy in a particular direction (in a 'beam') which gave the effect of using a higher power transmitter. Likewise, using such an aerial at a receiver minimised interference being received from the sides of an aerial and effectively amplified the signal coming from the desired direction. Shortwave 'beam wireless' stations made low power, long distance communications possible, very effectively and at much cheaper outlay than for longwave services.
Cable and Wireless
For Britain, having moved on to the use of Marconi's high frequency 'beam wireless' radio telegraphy caused an issue, brought about because beam stations were much cheaper to install than were the undersea telegraph cables of the day. Because of the significantly cheaper radio telegraph charges the cable companies lost business. Within 6 months of establishing beam wireless services the previous telegraph traffic carried by Britain's Eastern and Eastern Extension cable companies had dropped by 68% and on the Post Office's own Pacific cable route by over 50%.
Political lobbying and merging of Eastern and Marconi businesses ensued, the outcome in 1929 being a conglomerate called Imperial and International Communications - renamed Cable and Wireless in 1934. The Cable and Wireless merger produced a single company that controlled thirteen cable ships, 253 cable and wireless stations, more than half the worlds cable systems and nearly all the worlds high frequency radio stations. Britain was now firmly in command of global communications, any American challenge to that dominance being lost when the Wall Street stock market crashed in 1929 and the great depression set in until 1939.
Collier and Beale
In 1926 Messrs Percy Collier, a radio engineer and Gordon Beale an accountant established the company of Collier and Beale. Based in Wellington, they designed and built everything from domestic broadcast receivers to high power shortwave transmitters. Collier and Beale established a significant relationship with the NZ Post Office, as their products formed a core part of early NZPO coast station equipment.
For example, a standard 'pair' of transmitters were Collier and Beale 1000 watt and 100 watt devices, assigned as the primary and reserve transmitters for a designated service. At Awarua Radio one pair supported the 500kHz telegraph service and the other pair supported the Small Ships service providing amplitude modulated voice communications on 2182 kHz.
During the war years of 1939 - 1945 Collier and Beale worked on the development of radar systems and in 1942 produced the first of their iconic ZC1 portable receiver/transmitter devices for military use.
NZPO Beam Wireless Stations
During the 1930's and 40's the NZPO gradually added beam wireless systems to its coast stations to meet its international communications needs. An issue with beam wireless was noted on long range signal paths where marginal signals could fade in and out due to changes in the ionosphere. Also, the buildup of radio and electronic noise being created by cities had raised the electrical noise level making radio signals harder to receive. Moves to overcome increased noise and to minimise locally-generated transmitter interference were undertaken.
ZLB Awarua Radio Station
In the early war years Awarua Radio updated its services. Dropping of the old Telefunken mast in 1938 had cleared the way for the erection of three 150 foot self-supporting steel lattice masts and improved transmitter aerials. In 1940 a new Receiving Office (RO) was established along with the installation of new receiving antennas located in distant paddocks of the Awarua farm.
ZLD/ZLF Musick Memorial Radio Station
In 1942 ZLD and ZLF Auckland Radio were transferred from the Auckland Chief Post Office building to a purpose built facility, the Musick Memorial Radio Station located on a remote Auckland headland which was renamed Musick Point. The new ZLD receiving and transmitting services were separated by a few kilometres to minimise local interference the station might cause itself.
Makara Receiving Station
In 1944 a new site, Makara Receiving Station (Makara Radio) was constructed on lonely hilltops some 11 miles from Wellington. The large property of 2300 acres (930 hectares) allowed a significant number of aerials to be installed, including 54 inverted V's providing 360 degree directional reception, broadside arrays and rhombic antennas. The specialist equipment installed included triple-diversity receivers to counter international signal-fading issues. The concept of triple diversity is like having three separate receivers connected to three physically separated aerials (space-diversity), each receiver possibly being tuned to a separate frequency (frequency-diversity) where the same traffic information was being sent on all three frequencies. Automatic switching circuits could switch to the receiver that had the strongest signal at any time, thus minimising signal fading or dropout.
Himatangi International Transmitting Station
In November 1953 a new NZPO radio station was commissioned located on the Manawatu coastal plain. Himatangi International Transmitting Station (Himatangi Radio) was a solution to concentrating New Zealand's international radio services that had been scattered around its coast stations ZLD, ZLW and ZLB. Himatangi Radio worked in conjunction with Makara Radio and a controlling terminal located in Wellington. For voice circuits the International terminal would request receiver and transmitter services from Makara and Himatangi, then would connect the incoming and outgoing voice circuits as a telephone circuit to the Toll Room where traffic would be passed. Voice calls to ships, islands and other continents were all handled this way. International radio teleprinter traffic was handled in a similar way, while International radio telegraph traffic was remote keyed from ZLB and later from ZLW. Consequently there were no operators located at Himatangi.
Beam Wireless Services
New Zealand beam wireless provided radiophoto services to Australia and Britain (from 1947), radio-telegraph services to London (1952), Sydney (1954) and Vancouver (1959) and an international telex service (1960). By 1962 there were four voice channels to Australia and one each to Britain, Canada, the United States and Fiji.