THE WIRELESS WORLD

Otago Daily Times, Issue 21829, 16 December 1932, Page 4

THE WIRELESS WORLD

NEWS AND NOTES By Magna Vox. Items of_ local interest are invited by “ Magna Vox ” for publication in this column. It i« necessary that such matter should reach this office by Tuesday of each week for insertion on the following Friday 2BL, Sydney.—Bss K.C., 353 metres. 2FC, Sydney.—G6s K.C., 422 metres. 3AII, Melbourne.—62o K.C., 484 metres. 3LO, Melbourne.—S3o K.C., 371 metres. SCD, Adelaide.—73o K.C., 395 metres. 4QG, Brisbane.—76o K.C., 335 metres. IVA. Auckland. —820 K.G., 365.8 metres. Every day. 2YA, Wellington.—72o K.C., 420 metros. 3YA, Christchurch. —980 K.C., 306 metres. 4VA, Dunedin, —650 K.C., 463 metres. 4ZO, Dunedin. —IOBO K.C.. 277.8 metres. Monday and Friday. 4ZB, Dunedin.—loßo K.C., 277.8 metres. Wednesday, Thursday, and Sunday morning. ANSWERS TO CORRESPONDENTS. “ Four-valve,” Alexandra,—Your set is doing remarkably well, and under the circumstances I should advise you to leave well alone. Increase or decrease in the number of turns will not affect the spacing; it will only move everything up or down. A condenser of a different value or with differently shaped plates would be required. J. M. M‘C., Dunedin.— (!)• Using 24 d.s.c. wire, 60 turns. ■ Primary aerial coil, 20 turns; r.f. coil, 30-35 turns; reaction coil, 15-20 turns. (2) I am afraid I cannot enter into any controversy regarding the merits or demerits of any particular set. So far as I know, both firms are very reliable. “ Grid Leak,” Oamaru.—The value of the grid leak largely determines the capacity of the coupling condenser, which should have as high a value as possible, but this depends to some extent on the grid-leak yalue. It assists very materially in retaining the strength of the lower audio frequencies if this coupling condenser has a fairly high value. A capacity of 0.005, or even up to twice this amount, mav generally ,be used, while for the leak T megohm is an all-round useful value!

TOO MANY COUNSELLORS. The latest decision on the part of the radio authorities to disband the various advisory boards that have functioned for the last four or five years is probably sound. The decision affects both the Musical and Dramatic Advisory Committee and the Children’s Committee. All that will be left now is the Church Advisory Committee, which arranges church service rotas. While it is difficult to shed many tears at the passing of the other committees, it is only fair to add that in a modest, unobtrusive way they have served their purpose during difficult times (states the Dominion). The Musical Committee has been responsible for the arrangement to broadcast a number of interesting programmes on the part of the various musical societies concerned, not to mention the lead it gave to community singing. Radio in New Zealand to-day, however, is in a sufficiently advanced stage for the radio authorities to be able to continue to function quite satisfactorily without a multitude of counsellors. THE LEAD-IN., The lead-in should be attended to with great care. There, is not,much to be said against a good insulating tube passed through the woodwork of a window frame, providing that precautions are taken to prevent the' entry of rain or dirt. It is very nice, of course, to bring the lead-in through the centre of a pane, but not qveryone- can drill glass, and domestic arrangements do not always allow one to do it ! When the aerial has found its way inside the house, it must still be treated with just as much care. The set should, of course, be as near to the leadin as possible; but if a long journey for the ’inside wire cannot be avoided, see to it that it is kept well clear of walls and ceilings. Ebonite rods about Cin Ibng, with clips at,one end and pins at

the other, are obtainable for the purpose of fixing indoor aerial to picture rails, and are quite useful for dealing with lengthy leads-in.

SOME USEFUL RULES. In almost every art or science there exists a vast collection of , empirical formulae or rules of thumb which are in constant use —unashamedly by amateurs and dabblers, and surreptitiously by highbrow professionals. It is unfortunate (says a writer in an English radio paper) that our own art is somewhat deficient in these easily remembered rules,, and such as exist are open to criticism on scientific grounds. Nevertheless, there are a few that are worth while remembering, and which will be accurate enough for most practical purposes. For the benefit of readers, three of the best known ones arc enumerated below : (1) Wavelength is directly proportional to turns (in a tuning coil). This is a very useful rule. If, for example, a simple short-wave receiver can be tuned to a wavelength of 30 metres with a fourturn coil, there is little doubt that a wavelength of 15 metres will be receivable with a coil of similar diameter having two turns. (2) For a frame aerial wound in a more or less conventional manner, and of roughly the usual size, a total length of 75ft of wire will provide suitable inductance value for tuning to the medium broadcast band with a 0.0005 mfd. condenser. For a long-wave frame (1500 metres) a total of about 250 ft of wire would be necessary. (3) The correct value' of negative grid bias to apply to a three-electrode amplifying valve is ascertained by dividing “ h.t. voltage applied ” by “ twice amplification factor ” {of the valve concerned). This rule tends to become inaccurate when it is applied to modern valves of exceptionally high efficiency. RADIO EMERGENCY CORPS. A very important feature of the Radio Emergency Corps is the transmitting and receiving apparatus, which by nature of its duties requires to be very compact, light, and yet capable of transmitting and receiving over fairly long distances. This has proved a very difficult task for the equipment supervisors, but, after much experimenting and actual testing under very trying circumstances, both pieces of apparatus have been constructed and perfected beyond expectation. The transmitter and receiver designed and constructed for the Otago section of the R.E.C. by Mr W. Collett (ZL4BP) is built in two distinct separate units, one quite independent of the other as regards power supplies and aerial equipment. The transmitter circuit is a splitcolpitts, which has been found to have several great advantages over the usual circuits, the most important being its very great efficiency when using low power. Using a single receiving type tube with a filament supply of 0 volts and a plate supply of 90 volts, B battery, distances of up to 500 miles have been covered quite easily. The receiver is the usual type, two-tube, used by amateurs (one detector and one audio), all being enclosed, including batteries for filament and plate supply, in an aluminium case Win by 4in and weighing about 121 b. This receiver under favourable conditions is capable of receiving signals from practically every part of the world. Both pieces are enclosed within a small wooden case measuring Min by Min. It contains all necessary gear, including transmitters, aerial equipment, batteries, insulators, etc., and weighs approximately 301 b, making a quite comfortable pack for one operator to carry. All this equipment is operated on a special wavelength of 105 metres, and under special call signs. These privileges were given to the R.E.C. by the Government, and are to be used only for emergency use or for actual testing purposes. The recent numerous testa have been carried out throughout Now Zealand with very encouraging results, and have shown that the R.E.C. is nowready in every part of the Dominion for an emergency of any description. The personnel of the Otago section is as follows: —Section leader, Mr Ray Stroud (ZL4AP); assistant section leader, Mr A. Harris (ZL4CA); equipment manager, Sir W. Collett (ZL4BP); assistant equipment manager, Mr E. Cameron (ZL4BJ); secretary, Mr J. Wincfield (ZL4BY); operators—Messrs C. Morrison (ZL4CY), A. Petersen (ZL4CN), A. , Sparrow (ZL4BS), R. M'Connell (ZL4BV), K. Barron (ZL4DB), J. Callander (ZL4BT), and R. Robinson (ZL4ACJ.,

CHAIN BROADCASTING. The problem of chain broadcasting is not yet nearly as complicated in New Zealand or Australia as it is in the U.S.A., where chains extending from one coast to the other and including up to })0 stations have to be arranged. The programmes, which, of course, are sponsored, are generally arranged in units of a quarter, half, or one hour, and whereas one advertiser may require a chain of, say, 25 stations for perhaps a quarter of an hour the next may want 40 stations, some of which may not have been included in the previous period. Thus there arises the problem of arranging for all the stations which are members of the chain to drop in and out of broadcasts originating from the key station at the correct time without any ■ abnormal delays, for there are so many stations competing for the listeners’ attention that periods of “dead air” have to be avoided at all costs, and the aim is never to have silence for more than 10 seconds no matter what may be the trouble or the interruption in the system. This naturally . requires stop-watch co-operation between all stations belonging to the network; and everything is timed to the second. For example, it may be that at 9 p.fn. a programme of a certain type is to be broadcast through a group of stations'. At’, exactly 30 seconds before this time the announcer who is handling the preceding programme will close with “ This is the Columbia Broadcasting System,” or some such phrase, which is a cue for the entire network. Five seconds after this each station in the network will give its own call sign. Those announcements are usually made over a * background of music, which generally continues until 10 seconds before the commencement of the new programme, when it fades Out: /Then follows silence for 10 seconds, during which period the authority ■ known, ns “ Master Control ” disconnects the studio which has been used, connects up that which is to be used,.'and makes the necessary land-line' connections for pending out the coming programme to- the selected stations. Also during this period throughout the whole of the network stations which are leaving it drop out of the system, while those which are to come in make the necessary connections, those which are continuing on, of course, take no action. Then exactly at the hour the opening announcement or the opening bars of the new programme come on the air throughout all stations. This procedure has reached such a state of, accuracy that listeners may check theirclocks with the various cue words and opening times. Programmes are carefully rehearsed before they are allowed to come on the air, and during the broadcast the producer keeps an accurate check, and sees that it finishes neither too early nor too late for the arrangements to bo made for linking up the proper stations for the succeeding performance. The Columbia broadcasting system includes about 93 stations, extending from the Gulf of Mexico to Canada and from New York to California, and it operates from 7.30 a.m. one day to 2 a.m. the next morning. The difference in time between oast and west allows this, ami it is possible tor a'listener with a sufficiently good set to obtain reception practically throughout th, 24 hours, for when the Californian stations are closing down at 2 a.m. it is G a.m. in New York. Not all periods of the day arc‘sought after by_ advertisers, and it is necessary for stations during the “off” periods to put on what arc known as “sustaining” programmes. The key stations use these for trying out new nrogramines and new artists, and any station on, the network which happens to be short of a programme of its own may utilise these if it wishes. When such a programme has reached a satisfactory state of efficiency. it is handed over to what is known as the sales department, and it is sold to whatever advertiser may fancy it, when it takes its place in the more important hours of tlie day.