RADIO LINKS FOR TELEPHONES

Chronicle (Levin), 11 October 1946, Page 7

RADIO LINKS FOR TELEPHONES

—Press AssDciation

♦ Alternative to Lines And Poles

By Telegraph-

WELLINGTON, Oct. 10. Esta/blished. ior ' experimentai purposes to Keep New aeaiand abreast wiwi work overseas, a hign-irequency raaio telephone iinn with the ioouth i.siand irom Wellington iias been deveioped to tbe extent that it is now capaDie of providing an alternative to me submarme cabie system that i'ormeriy was tbe only metnod of telephone ana teiegrapn communication between tbe Nortn and South Islands. 4 ' Direct radio teokmquo otfers certain advanfages and is' likely to be used when tbe f uli . capaeity qf existing eables lias been reacked," said tlie Cluei Engineer uf. tlie Post Office (Mr. E. H. 11. ureenj, in connnenting on tbe work of the developniental stations. ' ' Kadio is by no nieans liinited to sea crossings, and niigbt have an applicatiou as an alternative to existing toll liue services. 4 4 An example whicb has received consideration is the link between Wellington and Palmerston North, wbere certain difficulties exist in duplicating the pole line, and where use might be made of the high ground near Wellington'to facilitate communication with the Manawatu plain." The work of the radio section of the Post and Telegraph Department on alternative methods of communication to carry telephone and telegraph traffic proved its worth last year when transportable sets built originally for use by the armed services were quickly brought into operation to take over the traffic between Christchurch and Ashburton, where the service had been disrupted by snowstorm damage to lines. The equipment providecl eight channels of ordinary toll communication for several months without the public realising that radio was being employed. The Wellington terminal of the developniental ultra-high frequency radio telephone linlt is situated in Buckley Road, Melrose, where a sniall building and aerials are the forerunner of whai will beeome an important part of the eoinnninic ations witli tlie Soutli Island, and even now provides a scrviee auxiliary to that provided by the snbmarine eables. Tlie southern station is situated at Seddonj and the distance covered is abont 40 miles. Links in sueh a system ean be longer, tlie main limiting faetor being the necessity for a elear 44vision" to the next link — the ultra-liigh-frequency radio used will not surmount obstacles and niust have a direct run to tlie receiviug station, so that aceessible hut dominating heights must be selected. In flat eountries overseas it has been nessary to build high pylons to give that uninterrux)ted radio "view", but it is expected that in New Zealand suitable heights on whieh to establish relay stations ean be i'ound. For instanee oue hill near r Ihxekak^i'iki giyes anliuniu|:er> rupted line to the slopes of Mount Egniont, so that for a system to couneet with New Plymoutli, that hill could be eonnected with Wellington by relays on hills with the tinui relay from Mount Victoria to the Chief Post Office, where Ihe conneetion would be made with the norma] toll service and the general telephone. "The Post Office is actively interested in the use of ultra-hlgh-frequeney radio communication as a possible nieans of extending the telephone network, " said i\lr. Green. During the last 10 years the Domiuion had kept in close toucli with overseas dcvelopments in the use of radio for telephone systems. The British Post Officc used rauio extensively across thq Irish Sea, to the Jsle of Man, and to tlie Cliaiinel lsJands; and New Zealand had been interested in tliose developineiits particuJarly in regard to tlieir possible apjilieation to .communication over Cook Strait, a vital link in New Zealand 's communication system. Safeguard Against Accident. Althougli tlie two liigh-frequency submarine cables linking tlie North and youth Islaiids provided adequate facilities for toll aud telegraph coininunications, it was tlie Department 's poiicy to exploit radio as a safcguard against the possibiiity of interruption, said Mr. Green. The Cook ytrait developniental link might ultimately be extended to Christchurch to give an auxiliary service in country that sulfers from storm and snow damage. The developmental unit was started in New Zealand two years ago with an experimentai single-channel radio-tele-phone across Cook Strait, and from that it had been developed to the stage where it had taken 12 channels in a test which was held on a busy day, he said. All the radio equipment was designed and built by the Post Office. The unit consisted of a receivcr and a Aansrnitter with highlv directional •lials in positions that gave a elear optical patli to the destination station. "Althougli it is not in regular use it iK known tliat the plant installed ex[lerimentally is quite capable of carrying the Department 's services if re(piired," eontinued Mr. Green. "It is proposed to put the radio link into coritinuous use with a sniall number of channels to give experience in its operation and to tesl its working. " "The system has been tested and proved capable of carrying the telephone and telegraph traffic under average busy eonditions," he said. "For tlie experiment the multi-cliaunel 'carrier' equipment . used with one of the submarine eables was temporarilv eonnected to tlie Melrose and .Seddon radio stations to enalile 12 telephone conversations, together with telegraph services. to be maintained over tlie single radio link." Asked about possibilities of interference to the service from atmospheric eonditions, AEr. Green said that use of the radio wmhl not be acceptable unless it conq)lied with the highest standards of communication. When thev had 12 channels in operation across Cook •Strait for the test, people had not known the diiference in the service. The processes of the "carrier" svstiem and tlie type of modulation employed made it virtuallv impossible for a cou-

versation over tlie system to be tapped. "Modern developments in long-dis-tance telephony are all in the direction of usiqg radio teclmique," said Mr. Green. He added that while circuits over land lines and submarine cables would alwavs figure largely in New Zealand telephone reticulatiou, there' was a distinet possibiiity of use being made of very high-frequencv radio cir•uits from pvlon to pylon or from hilltop to hilltop as an alternative means of providing trunk line communication, with a rcsultant increase in the reliability of the whole sysrem. ^