NEWS AND NOTES

Radio Record, Volume I, Issue 14, 21 October 1927, Page 8

NEWS AND NOTES

(By

Switch

Too much amperage drawn from an 4 accumulator is apt to damage it. The ‘Maximunr current which can be taken from an accumulator is one-tenth its total amp-hour capacity. ‘Therefore, a 60-amp hour (continuous use) bat‘tery can stand the drain of 6 amperes without damage being’ caused. "A ‘powerful one-valve amplifier for -use with a crystal set cam be made by inserting the B battery between the loudspeaker and the plate of the valve, with orie side of the loudspeaker connected to the plus of the A battery. ‘hus, one side ofthe loudspeaker is connected to the minus side of the B battery atid the other terminal of the loudspeaker is attached to the plus of the A battery. A wireless quarrel is shattering the night air for the European radio fans. ' The Soviets at Moscow every evening for some time have been broadcasting in Esperanto, but at the first phrases n strong French. station has cut into spoil what the French evidently think is propaganda. Moscow, experts say, frequently changes wave-length to find a‘hole in the air, but the French station, whose identity is kept secret, follows the Russians up and down the scale, and so far has prevented Moscow from getting out to France at feast more than a few phrases. Have you noticed the tremendous improvement in the transmission by SAR, Melbourne? The other evening this station was heard consistently louder and clearer than 2FC, Sydney, which has held the championship, so far as reception in Wellington applies. If you are in doubt as to the condition of your dry B batteries disconnect the aerial and earth from your set, and if you hear rustling or crackling sounds your B batteries have dropped too low in voltage. The batteries are then of no use, and can be thrown away. What factors make for the greatést efficiency of a receiviss, aerial? (11 The height of the aerial. (2) The length of the ‘aerial. (8) The efficiency of the insulation. (4) Freedom from any screening cffects " Generally speaking, »# short aerial gives greater selectivity to a set, but reception will not be so strong as when a Jong aerial is employed. An ideal fengsth of an aerial for ordinary broadcast reception is about 145 feet, in€luding the lead-in. The earth wire should not be longer tlun 12 feet, but the shorter it is the better, and heavy genge wire shonld be ased. ‘ Short-circniting on accumulator causes serious damage te it unless the circuit js very brief. It is far better not to test your battery by short-circuiting _ it to make a spark, as this does moze or less harm, The internal resistance of a batterv is so low that an enormous eurrent flows throuch it when it is short-circuited, and this results in backling. disintegration, and the baneful tulphating of the plates Glass has come into high favour as an insulator at matiy of the American experimental short-wave stations owned by commercial concerns. At KDKA "Pittsburg, Pennsylvania) it is used to insulate the heavy copper turns of the inductances; brass-tipped glass knobs Bupport various condensers on the panels, and gelass-air insulation has replaced older through-the-wall types. The glass-air insnlater consists of @rilled pvrex bell-jars placed on both sides of a cirenlar aperture in the window glass. Bv holtine the bells together, with ¢he holts centring in the aperture and the hells separated from the window glass bv ruhher gaskets, an effectively insulated hindine post is obtained. The words "primarv" and. "secondary’? as applied t- radio hatteries have grown into disuse. A primary battery embraces all dry cell batteries, and a secondary battery covers all tynes of wet batteries or accumulators, whether A or B. Sometimes crystals seem to lose their sensitivity. To restore its usefulness chip off a portion of the crvstal to bare i) fresh surface. ‘Then wash the crystal with pure alcohol or carbon disulphide. In any of our New Zealand cities a whole Jot of listening-in should be indulged in by the tramway authorities. They would find a host of wheels with flats on their tires, bad motors, halfcontacting overhead switches, and other ether disturbing factors. Following are the wave-lengths of the British broadcast stations :- Station, Wave-lengths Daventry c.sccssscecssseeee 1,604.8 Aberdeen — cvessscecese seees 500 Bournemouth .e.ccsecsceee 491.8 Glasgow — cecccacesceeeerecs . 405.4 Plymouth ceissssccreeseere 400 Manchester ..iccscesese i 384.6 London — ciccesesssesscsecee 861.4 Cardiff vccsccssececessees we 353 Birmingham ..viceeweee 326.1 | Newcastle -casssesessesee 312.5 | Belfast — .ciccccressssecevene 806.1 Taiverpool -sesesserseeeseeee 297 FLU] cscsesssessceveveeevees 294.1 Stoke — icccsccesscsseveveveee QVAVL SWANSEA -serevervenerceeenre 294.1 T)unlee ec accccecsesevvevece 294.1 Vedinburgl — cccsccesseeesee 288.5 Teeds wees senesepesvesuense 277.8 Nottinglian sasseesseee 275.2 Sheffield qrevsgnce¥roecoees 272.7 Bradford PUT ETITGe ai 252.1

Engineers of a South Carolina trac. tion company have discovered that it is possible to detect mechanical de fects, such as flat wheels, poor motors, etc., of street cars by erecting a radio antenna alongside trolley wires, and listening-in with an ordinary receiver. It is said the idea was conceived when listeners complained of interference in their sets caused by passing cars. An indoor "loop" or "frame" aerial should not be used with a neutrodyne set, but for any other circuit it is quite practicable. A square loop aerial for all-round broadcast reception can be made as follows:-Length of each side, 3ft.; mumber of turns, 8; spacing between wires, fin. Wire for an indoor "loop’’ aerial may be from 22 to 14 gange. When the wire is wound tightly there are dielectric losses which raise the resistance, When spaced several diameters apart it is immaterial whether the wire is insulated or bare When used in a room the proximity of an indoor ‘‘loop’’ aerial to the walls or ceiling has the effect of raising the effective resistance. The difference in resistance when the "loop" is 5ft. away from the wall is 20 or 25 per cent., as compared with that when near. If your audio-frequency yalves have a tendency to howl, separate all wiring as tar as possible to reduce inductive effects. Place the transformers further apart and arrange their wirings at right angles if possible. Also try reversing the connections to one or more of the primary windings of the andio transformers, and also experiment with connections from the iron cores of the transformers, either to earth or to the positive of the high-tension battery. Through permitting an accumulator (wet battery) to stand too long in a ‘discharged condition the plates will become encrusted with sulphation, which causes trouble unless removed. This coating reduces the active surface of the plates. In some cases sulphation can be removed by giving the battery a very long charge at a low rate, after adding a pinch of Glauber’s Salt to each cell. Next, empty out the acid, wash out the cells with distilled water, refill with fresh acid, and again charge the battery, this time at the normal rate. Sediment will sometimes be seen in the bottom of wet batteries. This should be removed. Charge the battery first, wash it out with distilled water, refill with acid, and finally give the battery a short charge. Sediment in the bottom of a wet battery generally indicates that it is being charged or discharged too rapidly. Some novices wonder how the broadcast waves get on to their aerial when it is insulated with cnamel. Electromagnetic waves pass easily through all insulating substances. The cords connecting an indoor "loop" aerial to a receiving set should not be more than 38 feet in length. ‘The cords should be kept well apart, A satisfactory ‘earth’? connection for a portable receiver can be made by connecting to an insulated wire stretched on the ground, instead of to @ poor or metallic ground, such as a tod driven into a wet spot. The best test for a new valve is to put it in a regenerative receiving set or oscillator and determine whether or not {t will oscillate, This is true, because a valve that will oscillate will also detect and amplify (the two other funetions of a valve), This is the test often used by manufacturers and dealers. A valve that will not oscillate is practically worthless for any use. but rectifying, N,