THE WIRELESS WORLD.

Otago Daily Times, Issue 19963, 3 December 1926, Page 5

THE WIRELESS WORLD.

NOTES AND NEWS. By Magna Vox. Items of local interest are invited hy “Magna Vox” for publication in this column. It is necessary that such matter should roach this office by Tuesday of each week for insertion on the following Friday. Those who are interested in the farmers' session at 4YA should note that in future, it will bo broadcasted on Thursday instead of Friday night. As this feature has become exceedingly popular among the farming community, it has been decided to extend the session to three-quarters of an hour. DID YOU KNOW-*-? That a small, singltvwire aerial is far more selective than a big twin aerial, and that in actual practice only a very slight drop in signal strength from inter-Stato stations will be observed. That a reliable variable grid leak is of very real assistance in long-distance reception, not only in obtaining maximum volume, but also smooth reaction control. That if accumulator acid is spilt on your carpel or suit ammonia should be poured over it at once to neutralise the acid. If no ammonia is available bicarbonate of soda will do. It should be sprinkled on, and then moistened with a little water. Keep adding fresh bicarbonate until tiro fizzing stops. WIRELESS EXHIBITION. The wireless exhibition, which, at the time of writing, is being held at Olympia, is undoubtedly by far the largest radio exhibition hitherto organised in Great Britain (states a London correspondent of the Sydney Daily Telegraph), and for the first time it is truly representative of the whole British wireless industry, owing to special arrangements which were made to accommodate all grades and classes of manufacturers and traders on an equal footing. My visit to the show impressed upon me the growing importance of the wireless industry, and the tact that from year to year the changes which take place all tend to show that broadcasting is taking its place as an essential public service. It was a pleasure to remark the amazing improvement in the quality of every type of exhibit. The eye is no longer offended, as has unhappily been the case at former exhibitions, by the sight of clumsy workmanship. and careless design, which only resulted in unattractive external appear ances. to say nothing of internal inefficiency. Visits to the show left a very satisfactory impression. Manufacturers no longer tried to catch the eye of the public by startling claims calculated to imnross those with little knowledge of wireless. It is realised now that the public has got accustomed to broadcasting and to what can bo achieved with modern apparatus, and the present tendency is for rival firms to compete with one another to win the confidence of the public on the merit of their products alone, and not by means of startling announcements and claims. The sets shown this year are of distinctly pleasing appearance. One must search in vain for the earlier typos -of sets, which consisted of an ebonite panel crowded with a miscellaneous collection of knobs- and switches. The tendency to-day is towards simplicity and neatness, and many new designs dispense with the necessity of an ebonite panel to provide insulation. PLATE VOLTAGE. A point which should bo observed in the use of a valve is the amount of voltage applied to the plate. There is in plate as well as in filament voltage a critical point which should not bo exceeded. All manufacturers state the efficient working plate voltage of their respective valves, and apart from that it is fortunately very easy to determine how much high tension voltage is required for a certain duty. Where soft or gas-filled detector valves are used a very pronounced blue glow will appear inside the valve. This is the danger signal, and should not bo ignored under any circumstances. As soon as it is seen the H.T. battery tapping for the detector valve should be immediately decreased. Finally, always handle the valves carefully; in spite of the improved robust construction of the modern valves, they still need a certain amount of intelligent care. Where general purpose valves are used throughout for all duties it is a golden rule to change them about in different sockets, until _ the best combination for tone and sensitivity is found. ATMOSPHERICS—THEIR CAUSE AND CURE. Although very great strides have been made in wireless development, particulary during the past five years, the difficulties caused by atmospherics have not been overcome. Very many and varied devices and methods have been tried, and some are in use, designed for the purpose of getting rid of the nuisance; but all these have failed. There arc certainly some very successful methods for limiting the effect of the interference —but this limiting always involves reducing the signal strength. It is possible to reduce the effect of atmospherics, but in doing so the volume of sound in the head-phones is also reduced. And it follows that to reduce the interfering signals —if atmospheric disturbances in receivers can bo called signals—to a minimum, the desired signals or sounds would also be reduced to a useless minimum. Therefore, a compromise must bo effieted. The failure to produce a device or method for cutting out atmospherics is due to a want of knowledge of the origin of the atmospherics. It is known that they are associated with changes in the electric state of the atmosphere ; they are worst when thunderstorms are prevalent, and are expericned most in the equatorial regions. But there is no scientific data as to their exact causes. That is the big handicap that faces the experimenter or research worker who attacks the problem of designing equipmentsimple and economical —for the purpose of leaving the receiver free to reproduce the studio items without the distorting and annoying noises It is generally recognised that atmospherics are electrical discharges in the atmosphere, invisible lightning—and these discharges act on the aerials like wireless signals, with the important difference that they have no regular wave length. And having no definite frequency or wave length, they cannot be tuned out completely. cannot be timed out, altogether, but it is possible to lessen the disturbance in the loud speaker. In broadcast reception the use of a small aerial is often very effective. The small frame aerial used with supor-hoterodynes and other sensitive sots is very satisfactory in counteracting the nuisance. With ordinary receivers such small aerials cannot be used unless the set is near a powerful broadcasting station, and other methods must be employed. One method is to connect a condenser across the aerial and earth terminals. A condenser across the loud speaker terminals will also bo of use. But the two main points to watch are an aerial that i= not too long and loosely coupled circuits. If the set is not home assembled wo cannot have any more loose coupling than the set will permit, except, in sets that. have aovablo coils. The aerial, however, can bo attended to. It must not be too long. Generally, a good length to use is 75 to 80 feet, including about 2u feet down lead. The higher the bettor. A crystal set requires a bigger aerial than a valve set containing two or more valves, because the crystal set gives to the ’phones only .what it picks up from the aerial, while a valve ect amplifies or boosts up the amount of energy picked up by aerial system. There have been times when most of us have found atmospherics, or statics, or X’s. as they are variously called, to bo good friends. When (bo sot does not work well on the evening that we invited friends to listen in, it was customary to blame the failure on the “statics.” _ Sometimes we didn't know and were quite honest about it. But times have changed. Wo know more about the set those days, and people know the familiar effects of atmospherics better. There' are, however, cases discovered by the traders every day, where the noises attributed to atmospherics are really caused by faults in the set or batteries. A battery (B battery) that is nearly run down will cause noises in 1 lie receiver not i unlike those produced by distant atmospherics or static discharges, A battery j having a voltage of ?2l volts will develop i those noises if the voltage falls below about 17 volts. When it is discharged to that extent it is time to got a now _ one. And that proves the necessity for having a small j voltmeter, so that one can toll readily bow the batteries are. Loose contacts between wires and their terminals, nv in the moving parts of a condenser, or in the valve sockets wil' also cause noises. The SFERAVOX reproduces with remarkable clarity, is free from distortion, and so constructed that no matter if the terminals arc connected the wrong way. the magnets cannot become dc-magentisod. £5 ss, off all loading radio dealers. —N.Z. Reps., Brown and Bureau (Ltd.), Wellington.—Advt.