THE WIRELESS WORLD.

Otago Daily Times, Issue 21147, 3 October 1930, Page 5

THE WIRELESS WORLD.

NEWS AND NOTES. By Magna Vox. 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 of each week for insertion on the following Friday, Metres. 7ZL, Hobart 535 3AR, Melbourne 484 4YA. Dunedin 463 2FC, Sydney .. ~ ~ '.. 442 2YA. Wellington . . .. .. 420 4QG, Brisbane ~ ~ 385 - 3LO, -Melbourne .; .. .. 371 2AB, Sydney ........ 310 2KY. Sydney .. .. .. .. 230 4ZO CHILDREN’S HOUR. WELCOME. 'The following 1b the eighth list of new members who havo-Jolned Uncle Ben’s Happy Radio-Family, and will shortly receive their badges:—Jack Drake,- 63 Malvern street, Woodhaugh; Adelaide Marett, Macandrew Bay.; Keith Altken, - 511 .Main South road, Caversbam; Pearl ..Simpson, Palmerston North; Annie Barclay, 7 Parkhlll-- avenue, Mornlngton; - Charlie Anderson, Wakart ; Edina Pettet, 18 Queensbetry • street, NorthEast Valley; Jack Marett, Macandrew Bay; Agnes . Barclay, 7 • Parkhlll avenue, Mornington; Geffy Hesse, Parkhlll avenue. Mornington; Bobby Grant,, Talnui; Jack M’Leotl, 46 Selwyn- street, North-East Valley; Noel Brooks, 96 Albany street. BIRTHDAY GREETINGS. Dorothy Booth, 58 Meadow street, Mornington; Jack M'Leod, 46 Selwyn street, North-East Valley; -Joyce Starr, 46 Maitland street; Noel Brooks, 96 Albany street; Sydney Roxburgh, 63 Malvern street, Woodhaugb. , . Uncle Ben and all the members of the' Radio Family also'send greetings to Grandma Riddle, Macandrew Bay Mrs Bramwell; Mr Barclay, 7 Parkhlll avenue; Mr Brown, S 3 Forth street: Keith Altken, 511 Main South road, Caversbam. . ■ COMPETITION. A' B C D goldfish—Abe, see de goldfish: M N O goldfish—Em en no goldfish; 3 A R Esa a are. Winners: Phyllis Mathewson, 15 Loyalty' street; Nancy Dale,, 107 Hanover street. A number of competitors were very near having the correct solution, so a number of consolation prizes will he given. OUR LETTER BOX. 10 Marquis street, North-East Valley. Dear Uncle- Ben and Aunt Alma,—l hope you are keeping well. I listen to your children’s hour, and: enjoy It very much. As I hea’r that you are having badges, I should like you to send three, please, as my brother and sister would both like one. I shall have- to close now, as It Is time to go to bed. Love to. all the aunts and uncles of our Radio Family, from your loving niece, EVELYN WEBB. [Thank you, Evelyn, for your welcome letter. We are pleased to hear 'that you enjoy our sessions. The three badges have been sent to you. Best-wishes from Aunt Alma, Aunt Dot, and Uncle Ben.] . _ ■ „ , „ Taler! Beach. Dear Uncle. Ben,—l would Hke to become a member of your family. We have a two-valva wireless set, and enjoy listening Into your children’s session. I would like you to send me one of your badges. I must close now, hoping that your children’s session will always be on.—l remain, yours sincerely, v LAURENCE JAMBS LIDDELL. , [Many thanks ’ for your letter, Laurence. You are very , welcome to Join our happy family. Your badge has been sent to you, son', and all at 4ZO trust that you like it. Greetings from Aunt Alma, Aunt Dot, and Uncle .Ben.] - ■ ' _ 40 Grey street, North-East Valley. Dear , Uncle Ben, —Thank you so very much for the badge. I think It la lovely. I wear It every day. I go to, the North-East Valley, School. I, am six years old. -My mother is writing this for me. I like the childrens hour on Thursday nights. Best love to Aunt Dot and -yourself.—Your wee Radio niece, DAPHNE JARVIS. , [Thanks, Daphne,, for your kind message. I hope you are getting on well at school. Daphne. Aunt Dot and Uncle Ben both send :thelr greetings to you.] Best wishes to the family, ; UNCLE BEN. ANSWERS; TO CORRESPONDENTS. Six Volt,” Waimate.—Your query in regard to your battery is covered in a special paragraph in this column. R. G. D., Dunedin.—The fault is certainly - not in your , speaker. The noise you complain of is probably due to electrical interference or an open grid . circuit in .the receiver, itself., Lightning, Milton.— The conductor must be of good, mechanical strength and_ electrical conductivity. Sharp bends ' are to be avoided, and the r ed should ( terminate in . a number of sharp points, and should, for preference. be separated ami plated from the building. The earth connection must be of low resistance, and made in soil which must be kept permanently moist; it must also be kept well away from all metal « work and places likely to be inhabited * a Expensive copper rods or cables ate not absolutely essential. _ If there are no high resistance joints,, galvanised iron pine will serve very well. ,f Home-built,” Ranfurly.—Yes, but you must remember that if the valves .are passing a relatively heavy current a drop in voltage along the wires must result. This can be offset by using fairly thick wire. Do not use thin wire, as, if the supply is taken to a valve at one end of a row. the last one may be receiving a voltage of from .1 to .2 less than the first. WUh main valves, which pass 1 amp. at 4 volts, the drop may exceed this, unless you use thick wire. Be sure that the heater pins of the holder .make good contact with the springs in the valve holder, as, if they do not, a further loss will occur., CARE OF ACCUMULATORS, accumulator generally has an efficient, life of about 18 months. After that the wet battery will not hold its charge for several reasons. ' In the first place the plates are liable to become bent, through constant heating and charging. Ihe paste falls away froth the plates, Jind lies at the bottom of the cell, where it shorts what small charge the accumulator might hold. The plates themselves become eaten away through the action of the acid. It will not help much flushing the battery out and replacing •the acid, because the plates are probably useless now. To repair the battery would cost almost as much as a new one, and the old battery would not be as efficient as a-new, one. You should, of course, make mire that the battery had ended its useful life by referring it to some reliable, battery service station. Test the specific gravity of the electrolyte with a hydrometer. There is no need to change the acid if its specific gravity reads as recommended by the makers of the battery. When adding acid to the battery, or when mixing fresh acid, use distilled water only, and add the acid to the water, not water to the acid, otherwise an explosion is likely to occur. The battery not be washed out with anything but distilled water; and it should not be left in a dry state, _s the plates, when drying, will buckle, and the paste will fall away at the slightest jar. The best plan is to take the battery to tbe makers in its present state. They will be able to advise you if the battery is worth further treatment. AUSTRALIAN LICENSES INCREASE. . There were 309,192 licensed listeners in the different States at the end of July, 1929, when the Australian Broadcasting Company, Limited, was given the contract for the supply of programmes from all the “A” stations. After that there was, for a time, a period of stagnation, with a definite falling off of licenses, in Victoria, and only slight increases in New South Wales and the other States. The big increases in new licenses during the post two months has brought the total for the Commonwealth to 335,037. ihe States increase for the past was as follows:—New South Wales, 17,888; Victoria, 4430; Western Australia, 3176; South Australia, 2890; Queensland, 1829. During August there were 5934 new licenses issued in New South Wales, and only 605 cancellations, leaving the net increase for the mouth 5328. In Victoria the new issues were 6090, and the cancellations 2626, the net increase being 3464. The new issues in Queensland were 1132, and the cancellations 543, making the increase 589 Australia had 1777 new licenses, and_6s2 cancellations, leaving the increase 1123. In Western Australia there were 757 new licenses, and 90 cancellations leaving the net increase 067. Tasmania’ had an increase of 860. tile new issues being 026 and the cancellations 60. Victoria. with its total of 147,180 licensed listeners, still holds the record per 100 of population for the Commonwealth, the

percentage being 8.25. New South Wales, with a total of 120,673 licenses, has a percentage of only 4.86, showing that there is still considerable leeway to be made up in this State. Queensland has a percentage of 2.59, the total being 24,217. South Australia has the same percentage as New South Wales, the-, total being 24,217. Western Australia, with' 7298 licenses, has a percentage of only 1.75, whilst Tasmania has a percentage of 3.45, the total being 7442. The average percentage for the whole of the Commonwealth is 5.21. OBTAINING SENSITIVITY. When sensitivity is the first consideration it by no means follows that the modern type of low-impedance detector will yield best results when used on the anode bend principle, and followed by resistance coupling. Generally speaking, the best all-round performance, combined with effective detection of weak .r medium-strength signals, will be afforded by an efficient valve of fairly high impedance—from 20,000 to 30,000 ohms or even more (says the Wireless World!. A valve of this type would generally be used with an anode resistance of up to a quarter of a megohm; this value cannot be greatly exceeded without risk of impairing the reproduction of high notes. When planning a sensitive receiver of the type under consideration, it is hardly possible to better the followmg;—A valve impedance, 25,000 ohms, with an amplification factor of about 25; anode resistance, 250,000 ohms, anode by-pass condenser, 0.0003 mfd. These constants are chosen with a-view to effecting -what _is . generally regarded as the best _ possible _ compromise between the conflicting claims of detector efficiency, high-note loss, grid circuit loading due to reverse reaction effects, and the separation of H.F. and L.F. components the detector anode circuit. Highefficiency valves with impedances of from about 7000 to 12,000 ohms have a theoretical advantage where quality is the first consideration, largely because it is -possible .to >, operate them effectively with a comparatively low value of anode coupling resistance. " EFFICIENT AERIALS.* the early days of broadcasting it was the ambition of every amateur and. experimenter to provide himself with a high aerial of as nearly as possible the maximum 100 ft length. In these days' of valve developments, however, it has been found that the old “P.M.G. aerial 1 ’ is generally , far too long, and much better results are_ obtained with a shorter aerial. Many listeners actually prefer an indoor aerial, and of those who. use an indoor aerial a considerable percent-' age have quite short antennae, not more than perhaps 10ft to 24ft in length. One ot the great advantages' of the shorter aerial is, of course, the increase in selec--I°% * s B eneral| y obtained thereby. With high-frequency amplification so very easy to obtain, by means of screen-grid valves, the possible reduction in incoming signal strength is quite unimportant, whereas the question of selectivity with increasing stations' becomes’ increasingly important. If you . are in doubt about the length of yqur aerial, it is a good plan l to try- using shorter aerials. A simple way to do this is to . disconnect the regular aerial from the set, and to ng up (a little distance away from the regular aerial) a temporary aerial consisting of a length of ordinary copper wire suspended on insulators, of course, in the usual way. It is better, if you want to make the test in the most satisfactory way, to take down the regular aerial and substitute thg temporary one for it, as, of course, the presence" of the regular aerial interferes to a~slight extent with the results which you get with the. temporary one. However, if it is too much trouble to take down the regular aerial, fix up the temporary one as far away from it as you can, and then proceed with your tests. The temporary aerial may be niade a few feet shorter than the regular one to start, ■ with the results on the_ receiver carefully noted.’ Then try cutting - off . a few more feet from the temporary aerial, and again note results both as-regards signal strength and particularly selectivity. In reducing the length of the aerial, of course, you cut off at the end remote from the down lead, and re-attach to the insulator at that end in each case. It is a good plan to have the insulator attached to a rope so that the reductions in length of the. aerial are compensated for by increases’in the length’of the rope. By a few trials in this way, and also trying different heights, you will soon find out whether there is going to be any great advantage in making a change in the length of your aerial. If the aerial was already comparatively short,, probably you . will not_ find a great deal of difference, but if it • was the old-fashioned long aerial it is almost certain that you will find a great improvement, especially in selectivity, by shortening it. Having discovered more or less the best dimensions you can then set to work to alter your regular aerial to correspond, finally re-erectmg it in its new form.