THE MAGIC SPARK.

Auckland Star, Volume 55, Issue 63, 14 March 1924, Page 13

THE MAGIC SPARK.

"SEARCHING" FOR DISTANCE. THE AUCKLAND RADIO ASSOCIATION. £ SlTini-SEXSITIYE MICROPHONE. PIDE BAND TRANSMISSION". (By "PHONOS.") A wire was received in Auckland this we ek from the Postmaster-General stating th:it he was prepared to place a bill before the house this session giving power to proceed with the suggested broadcasting scheme. provided all arrangements therefore were in train. It is only recently that reception of American concerts was quite a unique feat, but now- several local radios report regular distinct reception. }lr. 11. i Messenger, using a. four-valve set, and usually one stage of radio frequency reports that he finds no difficulty in enjoying complete programmes. Jilr. Edwards, of IAA, informs \is that from his station he has successfully worked 3BD (Mr. E. H. Cox, Gibson Street, Melbourne), his signals being mute clear. Other amateur stations in Ifew Zealand accomplishing the same feat are 2AC, 2AP, 3AA, and 4AA. Incidentally, through the courtesy of Mr. Edwards, Dr. Burst, of Hawera, who was recently in Auckland, carried on from bere very successful conversations with his own station in Taranaki. THE AUCKLAND RADIO ASSOCIATION. Last Wednesday's meeting achieved an objective which marks a distinctly nro'Tessivc step in connection with local radio development. There is now in being a body for the specific purpose of watching and forwarding amateur - interests, and when the local association grows, as every radion recognises it must do, and when it amalgamates with similar bodies now being established in other centres, wireless amateurs in' the Dominion will be assured of the activities of a body united enough to safeguard their welfare. Unanimity of policy among all listeners-in is essential if the future of wireless is not to become a monopoly of the dealers, or of that powerful body that has exerted such an influence in England and Australia. A keen executive has already the support of about ■ a hundred financial members, and it is hoped that within a month this number will be quadrupled. There was quite a warmth in the debate regarding the admission to executive positions of those financially interested in wireless dealing. The final decision, carried by an overwhelmin" majority, was to place no restrictions upon membership. Undoubtedly, under present conditions, it was a wise one, aud the present committee of the association is the stronger for it. It is hoped to persuade the Mayor of Auckland to accept the presidency of the association. HOW TO SEARCH. The set owner of to-day has one great ambition —the achievement of distance ' reception. The following hints in connection therewith will be of very general use:— When searching for long-distance*sta-tions, the reaction coil should be coupled to the aerial just tightly enough to cause the set to be on the point of oscillation. At this point, carrier waves, when picked up, will be stronger than if the reaction and aerial .coils are tightly coupled together. On picking up the carrier wave, tune it in as strongly as possible, and then decrease the reaction coupling to bring in the telephony, keeping the "silent point" of the carrier wave in tune the whole time. This will need slight adjustments on all condensers, so the greatest care must be taken. Otherwise the carrier wave will he lost altogether. Though reflex, circuits are undoubtedly §ood, and have proved very useful, even receiving America on one or two valves, this type of set is not recommended as a transpacific receiver, owing to its un- i certainty of operation where reaction or H.F. valves are concerned. For this Teason, the simple, more orthodox cirsuits are preferable, as they are, as a. ■ rule, more easily handled than their more efficient, though moody brothers. Do not expect to receive America as soon as you begin to tune inpas, more likely than not, you will have to '"search" for twenty to thirty minutes, or even more, before anything is heard. SIDE BAND TRANSMISSION. So much interest is now being taken in a recent development termed side hand transmission that a brief reference to its method of application is apropos at this time. A modulated carrier wave consists of a carrier frequency component, the upper side hand extending to the carrier frequency, plus 3000 periods and the lower side band extending down to the carrier frequency minus 3000 periods. The transmission of the carrier frequency component invilves an unnecessary loss of power, so therefore only one side band is transmitted, which, if due to a simple sine wave, only requires onesixth of the power of the complete modulated wave. As all the frequencies except those in one of the side bands to be transmitted have been eliminated byfilters, it is necessary to introduce again the. carrier component at the receiving end before detection. If the side band is applied directly to the receiving tube the signal on the output circuit would he unintelligible, because it is proportional to the square of the input, and consequently would be of double frequency. THE EXTENT OF THE RADIO INDUSTRY. An idea of the extent of the growth of radio manufactures may be gleaned from the following official American figures for 1923: —The gross purchases of radio apparatus for that year aggregated more than £22,000,000, while the value of radio tubes sold approximated one-third of the value of all electric light bulbs disposed of during the same period.