THE WIRELESS WORLD

Otago Daily Times, Issue 21987, 23 June 1933, Page 2

THE WIRELESS WORLD

NEWS AND NOTES

By Maona Vos.

Items of local interest are invited by “Magna Vox” for publication in this column. It is necessary that such matter should reach this office by Tuesday ot each week for insertion on the following Friday. 2BL, Sydney.—Bss K.C., 353 metres. 2PC, Sydney.—66s K.C., 422 metres. 3AR, Melbourne.—62o K.C.. 492 metres. 3LO, Melbourne.—B3o K.C., 371 metres. SCL, Adelaide.—73o K.C., 395 metres. 4QG, Brisbane. —760 K.C., oSS metres. XVA, Auckland—B2o K.C., 365.8 metres. 2YA* Wellington—72o ICC.. 420 metres. 3YA, Christchurch. —980 K.C., 306 metres. 4YA, Dunedin—6so K.C., 463 metres. ANSWERS TO CORRESPONDENTS. E. T. M‘G, Dunedin.—The length of the winding (i.e., the gauge of the wire) has an important effect, and tor this reason the figures have not been checked. Nos 1 and 4 would be satisfactory tor No. 20 d.s.c., and No. 5 would vary with the effective diameter of the winding, but seems satisfactory. iNo. 6 should be about 70 turns. “Bias,” Anderson’s Bay.—No valve should be under-biased, and to apply too little bias is to increase greatly the anode current passing through the valve. This in turn decreases the useful me of the valve, and increases the draw on the H.T. supply. Besides this, it is frequently a cause of distortion on loud transmissions. The most serious consequences may occur when the grid-bias negative plug is removed from the battery in order to make an adjustment, or perhaps the plug may be knocked our accidentally. In such a case the valve is left without nnly grid-bias at all, and the anode current rises to a very high figure. Be careful always when altering the grid-bias voltage to switch off either the H.T. or the valve filament. High amplification detector valves are sometimes microphonia —a trouble which manifests itself as a howl that gradually builds up after the reception has been switched on for a time, and which may commence ns the result of a slight ]ar to the set. “ New Listener,” Gore. —You must examine the variable factors on your set before attempting to receive the more distant stations. If the aerial has a selectivity condenser, adjust this to the known most favourable position; or, if you are uncertain how it should be set for the beet all-round foreign reception results, leave it set in a midway position until you have # found it advisable, by preliminary tuning, to increase > or decrease the sharpness of the tuning. If the set hag a local distance switch, it must, of course, be placed in the j instance” position. But before this is done a note should be made of the exact dial readings of any stations that can be heard on the “local” position. It may prove to be much easier to determine the exact dial position when the switch is on “local,” and as such exactness is the* essence of tuning it ia necessary to get every station as accurately placed as possible. AN INTERESTING BROADCAST The Vacuum Oil Company, Pty., Ltd., has recently secured the exclusive rights to a series of particularly fine gramophone records entitled “ Viennese Nights,” which are recorded in the atmosphere of a European beer garden. Each record will be played once only from Station 4ZL on Monday evenings at 8.45 p.m. Each record measures 16 inches, runs at a speed of 33 1-3 revolutions per minute, and takes approximately 13 minutes to play. The series will be continued throughout a period of approximately six months, and should prove very popular amongst listeners. THE WORLD’S LISTENERS. Figures issued by the International Broadcasting Office, Geneva, show that at the end of 1932 there were more than 160,000,000 listeners.in the world using at least 40,000,000 receivers. The United States is at the head of the list for both number of listeners and number of receivers; but Denmark has pride of place for density (140 per 1000 inhabitants); U.S.A. (138.34) is second, Great Britain (117.5) third. Canada (66), Australia (63.88), and New Zealand (58), occupy ninth, tenth, and eleventh places in the world’s list. SHORT-WAVE. “ CATCHES.” . Hand-capacity effects may be present on the broadcast waves without being noticed, as the change of frequency they cause will be very small indeed. When we go down below, though, and the effect is 10 times as great we certainly do notice it; and when we get down to 15 metres (20,000 k.c.) and it is 20 times as great, it begins to be serious. The reason is that the length of the earth lead on the average short-waver is such that the set is not really earthed at all, A short-waver with an earth lead 20ft long is rather like a 300-metre receiver with 200 ft of earth lead; And if the set is not stable “ hand-capacity ” and “ head-capacity ” troubles begin to assume worrying proportions. By the way, I heard of a man who cured “ headcapacity ” (that awful effect that causes signals to disappear if one moves one’s head or handles the ’phone cords) by sitting in one of those ultra-modern chromium-plated chairs, duly earthed. One can sum up most of the troubles that appear to be peculiar to shortwaves by saying that they are still there on 300 metres, but that, on account of the lower frequencies being dealt with, they don’t show up.

SUNDAY TRANSMISSIONS. Listeners will be pleased to learn that Sunday hours have been increased at all stations since Sunday last. A morning session has been introduced, starting at 9 o’clock and extending to 11 o’clock. This consists of popular music. After closing down at 11, the stations reopen at 1 o’clock, and continue to operate till 4.30. From 1 to 2 o’clock music of ! the dinner-hour type is broadcast, after | which the Sunday afternoon’s programme ‘ of the character now well established is given. Few listeners realise what the extension of Sunday programmes involves so far as the radio authorities are concerned. Apart from the considerably increased hours for the broadcasting staff, these extra hours involve an appreciable additional expense. Longer hours mean more wear and tear on the machinery, more wear on valves, and increased upkeep all round. As trails- j mitting valves may cost anything up to £2OO, this matter is not unimportant. I Moreover, extended hours means an ; additional burden on programme expenses, It will be seen, therefore, that although there may be innovations that the radio authorities might wish to introduce, until they can see their way to finance alterations the ideal way may have to give way to a compromise. There is little doubt that the increased license returns this year have played their part in this much-asked-for improvement to the Sunday services. THE ROYAL BROADCAST. Although the announcer’s voice was heard with comparative clarity, the broadcast last week of the King’s speech | and that of Mr Ramsay MacDonald at | the opening of the World Economic Con- j ference in London, recorded by the Blatt- j nerphone process, was disappointing to I New Zealand listeners. The records ' were broadcast from the Empire short- ; wave station at Daventry, England, and were rebroadcast by the four national; stations in the Dominion. The signal strength was much greater than that of the short-wave transmission of the actual opening of the conference in the early hours of Tuesday morning (New Zealand time), but the recorded speeches were distorted, and only occasional portions of them could be distinguished. It is stated that although the recording process used is remarkably effective over distances of up to 500 miles, quality of reception deteriorates over greater distances. During preliminary testing for about three-quarters of an hour before the rebroadcast began reception is under- j stood to have been good, the announcer’s voice coming through with remarkable 1 clarity, but as soon as the recorded j speeches were put on distortion occurred. GROWTH OF LISTENING. | Through the courtesy of the general manager of the Broadcasting Board the Auckland Star publishes the following interesting table, which tells effectively, if only in figures, of the growth of listening in New Zealand over a period of eight years. It is remarkable how each

month, exclusive of the first one of thq radio year (April) shows a steady increase. Particularly pronounced jumps mark the opening of new YA stations and some of the Christmas periods, showing that radio sets must have been, as they still are, appropriate presents at this season. Here are the figures for each year ending March 31 since 1925, with any special feature bearing on them: —

1925 4702 (the fee was then ss, and broadcasting was conducted by enthusiasts and supported by contributions from the small number of dealers then existing). 1926 — 3588 (In this year the company took control, and the license fee became 30s). 1927 — 18,162 (IYA and 3YA opened). 1928 — 39,315 (2YA opened).

1929 1930 1931 1932 — 74,741 (the board took control for the last three months of this year). 1033 —93,914 (the first complete year of board control).

The above figures do not include the free licenses issued to the blind, to schools, etc. It should be noted that the greatest increase in one year was the Jump of over 21,000, which _ occurred during the year when 2YA first came on the air. This phenomenal increase is closely followed by the one in the year just past, when over 19,000 new licenses were added to the list —this, too, in the year of severest financial depression. Figures suggest that the radio trade has not experienced the bad times that many other concerns have had to face. But the outstanding story in these figures is the steadily increasing popularity ot listening. A much smaller ratio of increase than has occurred in any of the last eight years will be needed to carry licenses over the 100,000 mark, a total which in all probability will be reached before next Christmas. The opening of the new 3YA should give considerable impetus to licensing in the South Island within the next six months. SUBSTITUTES FOR AERIALS. Many devices have been tried for doing away with the aerial which, in fact, are really substitutes for the aerial. Probably many of you will remember the arrangement of a metal disc adapted to ba placed under the ordinary house telephone instrument and connected to the aerial terminal of the set. Although the lead from the metal disc to the set might have been only a few feet in length, actually you were getting the benefit of the telephone line, which sometimes acts as an excellent aerial. Another rather interesting case is where the set is used fairly high up in a building of several storeys, with a long earth lead (which may be a gas pipe or a water pipe), and without any aerial proper. In this case excellent signals arc often received, aim it would seem perhaps at first sight that the earth was acting better than an aerial. In point of fact, of course, you can regard the “ earth ” lead in this case as an aerial, but the set is perched at the top end of the aerial instead of being in the usual position at the lower end. In spite of all the different kinds of aerials and aerial substitutes it seems pretty well established that for the best results you must have some kind of vertically extended conductor. It doesn’t seem to matter very much whether you treat this as the aerial or the earth, or whether the receiver is at the top end or the bottom end, or what, so long as you have this conductor with one part at a substantially different height above the ground from another paVt, so that srou5 r ou can get high-frequency oscillations excited in it by the passage of radio waves. DETECTOR PROGRESS. Every listener knows that the process of detection is essentially one of rectification. Both the crystal detector and the diode valve detector operate as simple half-wave rectifiers, while in the threeelectrode detector a certain measure of amplification is also obtained. Thus the leaky grid detector acts as a half-wave rectifier plus a low-frequency amplifier, while the anode bend detector is, in effect, a high-frequency amplifier followed by a half-wave rectifier. With the diode rectification is practically perfect, but so far this system has not achieved any great measure of popularity, because it necessitates an additional valve, and thus adds to the cost of the receiver. Two diodes operating in push-pull to give fullwave rectification form an almost ideal system of detection, but there is still the feeling that a certain amount of voltage amplification should be provided in the detector stage. The solution of the problem will be in special valves in which one or more diode rectifying elements will be combined with an amplifying electrode system. Several variants are possible—single diode combined with either triode or tetrode, and doube diode combined with a triode or tetrode. In the double-diode-triode, which represents possibly the most useful combination, a single cathode is employed. Two small anodes serve for the full-wave rectifying portion, and the rectified output is then passed to the control grid of the triode portion, which has its own anode and operates as an audio-frequency amplifier. Thus, detection and amplification are kept entirely separate within the one bulb, the triode portion of the valve being electrically screened from the rectifying element to prevent unwanted coupling. The same type of valve can.be employed in other ways. For example, one of the diode anodes can be used for half-wave rectification, while the other serves for introducing automatic volume control.