THE WIRELESS WORLD

Otago Daily Times, Issue 23706, 13 January 1939, Page 2

THE WIRELESS WORLD

NEWS AND NOTES By Magna Vox Items ot 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 lor insertion in the following Friday IYA. Auckland.—oso K.c.. 401.2 metres 2YA. Wellington.—s7o k.c.. 526 metres 2BL, Sydney.—74o k.c.. 405 metres 2FC, Sydney.—olo k.c., 476 metres OAR Melbourne.—77o k.c.. 390 metres SCL, Adelaide.—73o k.c.. 411 metres 4QG. Brisbane.—Boo k.c.. 311 metres 3YA. Christchurch.—72o k.c. 416.4 metres. 4YA, Dunedin.—79o k.c.. 379.5 metres 4YO. Dunedin.—ll4o k.c.. 261 metres ANSWERS TO CORRESPONDENTS W. D, 8.. Dunedin.—There may be a valve which has a tendency to become microphonic, but it is more likely that the voice coil in your speaker needs recentring. In the particular make ol speaker you are using there should oe a washer included underneath the spider—between it and the end of the pole piece into which the locking bolt to hold the spider in place is screwed If there is no washer there, then put one in. To re-centre the coil, cut half a dozen ot so 4-inch strips of fairly thin cardboard, and carefully push these between tire voice coil and the speaker pole piece Then re-tlghten the bolt holding the spider in place. Finally, remove the cardboard, and the speaker should be accurately recentred, ‘ Dusty,' SI. Leonards.—ll is not essential to cover in the back of a set to keep out the dust. In fact, if .he receiver is a very small one, it is vise to leave it open so that the set will not become overheated There would however. be no harm in building a light frame the same size as the back ol the cabinet, and covering it with butter muslin. A RADIO AND CLOCK For those who each morning feel the urge to hurl the alarm clock through the bedroom window, radio manufacturers are offering a clock and radio combination. The receiver is a six-valve affair ouilt into an exceedingly compact chassis, but the usual dial is replaced by a clock face, on which the electric clock shows accurate time. The two mechanisms are inter-linked and one can pre-set the apparatus so that one’s favourite station is brought to sufficient volume to waken one at the desired time The receiver can also be adjusted to turn itself off at any. desired time, thus affording, according to the manufacturers, an opportunity of enjoying “ soothing lullabies ” on retiring without fear of leaving the set operating all night. CONTINENTAL REGULATIONS Stockholm forbids the use of “ loudspeakers " between 11 p.m. and 7 a.m., and Copenhagen will not allow excessive volume after 10 p.m. An interesting case is reported from Belgium There is apparently no regulation for dealing with reproduction which becomes a nuisance, but one set owner who persisted in loud reproduction was held to be giving a public performance, and, therefore, liable to copyright royalties to the pomposers whose works were being “ broadcast.” NO CHANGE YET Speaking to a meeting of shareholders of Amalgamated Wireless (Australasia), the chairman (Sir Ernest Fisk) said he believed that radio broadcasting in its present formtransmitting entertainment and news by sound—would continue for at least another 20 years. Some years of further development would be required before television could be made available to the public, either in Australia or elsewhere, on any large scale. A RECORD SEASON

The chairman of the Australian Broadcasting Commission, Mr Cleary, states that the season just closed has been a record one for paid to visiting artists, but the financial result of the concerts has been to make available for programmes many thousands of pounds more than would have been obtained had the recitals been confined to studios only. Next season, by acting in co-operation with private concert promoters, the Commission hoped to give a greater selection of artists at less expense than had been entailed this year. NOVEL AMPLIFYING SYSTEM An amplifying system has been installed in Westminster Abbey, Six microphones are connected with over 20 loudspeakers cunningly concealed in .different parts of the building, and this sound reinforcement carries the voices of the clergy all through the Abbey. THE. SHIELDED LOOP The loop or frame aerial in a modern adaption may come back into favour for broadcasting receivers as a result of research conducted by a big electric concern in U.S.A This company has produced a shielded type of loop, which, it is claimed, is as effective as a good indoor aerial, and results in substantial reduction of “ noise." The unit as applied in receivers In America, consists of 21 turns of wire on a frame lo£ inches high and 7.} inches wide, enclosed in a special type of shield which is the leading feature of the design The shield is a cylinder with metal discs at top and bottom, the side being made of coarse woven material, which has its vertical threads made of wire and its horizontal threads of an insulating fibre. Every vertical wire makes electrical contact with the top disc, but only one wire is connected to the bottom disc. The unit is mounted rotatably within the cabinet of the receiver. Loop aerials at one time were, fairly widely used in broadcast receivers, but the desire for distance with freedom from noise caused their disappearance. They are found in various forms in commercial communication, especially navigation Their directional properties are vain able, and they figure largely in dire-tion-finding schemes. The properties of loops and the effects of shielding have been known for a long time, but the problem was to find an effective design for the purpose in view The shield has to keep away only one component of the signal, the electrostatic component, and allow as much of the other component, the magnetic component, to enter as possible. This can only be achieved by spreading metal over as much as possible of the shielding surface and avoiding closed conducting circuits. Hence the, structure which has been referred to above Obviously, a shield of this type cannot be perfect, but careful design can materially reduce the effect of “ noise ” radiation from nearby sources, and because of the directional properties of the loop, further reduction can be made by rotating the loop until the response from the principal “ noise" source is zero or a minimum The shielded loop is installed in the receiver. the winding thereof replacing Die usual coil in the input circuit of (he first valve It is “tuned" along with the signal frequency and other tunable circuits of the receiver When the receiver is first installed the loop is rotated and left in the position of minimum noise pick-up. Apart from the fact that use of the new loop removes the need for the troublesome and often unsightly indoor or outdoor aerials, the advantages claimed for it by its originators are that it is a better aerial because its design is correlated with that of the receiver, and subsequent moving of the receiver does not affect its balance and requires no adjustment beyond, perhaps, the alteration of the direction of the loop to avoid a new noise source. It is con- ( coaled within the cabinet of the receiver, which it makes completely self-contained and portable It has valuable noise discriminating properties. It cannot compete with a good outdoor aerial for distance-getting, but is should act admirably for goodquality signals from relatively strong local stations.