THE RADIO WORLD

Southland Times, Issue 19757, 3 February 1923, Page 15 (Supplement)

THE RADIO WORLD

e WIRE AND SKIN EFFECT As wire, strangely enough, forms so large • and important a part of a “wireless” re- * eeiving set, the amateur will do well to ; learn a little about that material before con- ’ necting up apparatus. ‘ An electric circuit may be likened to a ’ system of pipes and the electric current to ! a fluid passing through them. The quan--1 tity of liquid which passes through a pipe in a given time depends upon the pressure l>ehind it, modified by the resistance of the inside surface of the pipe, and upon the I d lameter of the pipe, or, precisely, upon ihe cross-sectional area of the pipe. The surface resistance is obviously in proportion to the length of the pipe. Similar factors gov ern the quantity of electricity which flows in a circuit in a given time, for the current depends upon the applied pressure and the resistance of the circuit. In fact, the law regarding direct current is simply that the current in the circuit is arrived ■ at by dividing the pressure by the resistance. Electrical resistance to ordinary direct current depends upon the length of the wire and the area of the wire’s cross-section. The first factor increases the resistance and the latter decreases it. Some wires, being better conductors than others, possess an inherent tendency to pass current more freely. This property belongs to the material from which they are made ai|d is in no wise associated with thejr dimensions. Bearing in mind that resistance dissipates electrical power by degenerating it to the form of heat, we recognise that for efficient wiring we must use the best kind 1 of wire, that we must use as little as possible, and that it must be as thick as possible. All these counsels follow logically from the foregoing explanations. The currents which flow in the oscillating circuits of a wireless receiver art not simple direct currents, but high frequency alternating currents. The resistance which is offered to such by a given circuit is greater than that offered by the same circuit to a direct current. The reason for this is because a high frequency current does not penetrate throughout the entire body of the 1 wire but it confined largely to an area | nearer the wire’s surface. It flows, so.to) speak, only in the skin of the wire, the phenomenon being called the “skin effect.” The inside or core of the wire is practically useless in such a case and a metallic tube would serve equally well. In fact I have seen copper tubes used as conductors for wireless work. The moral to be drawn from the skin effect is that we must provide as much ; skin as possible for the high-frequency currents to flow in, though not necessarily ; by using inordinately stout wire. In practice, wire composed of many , strands braided together is used, or where convenient broad copper straps.

For general electrical purposes copper is the conductor which serves best the requirements of both conductivity and economy. For aerials, seven-stranded copper or bronze wire should be used and the same for the earth-lead. For connecting up oscillatory circuits some kind of manystranded enamelled wire insulated should be used, and for joining up various units it is convenient to employ stout copper straps. It should be stated, however, that in making receiving inductances single strand wires are generally used, the number of turns and the diameter of the wire being essential figures in the formulae employed in the design of the inductances. HINTS FOR AMATEURS Have you ever known a short circuit that was caused by the plate lead coming into contact with the grid wiring in such a [manner that a valve was burned out, This often happens if your “B” battery negative is joined to the “A” battery positive at the filament connection. A small flash-

, lamp bulb in series with the high voltage makes a good fuse. Be sure to choose a , lamp which does not consume more than .5 . of an ampere. Have you an old Ford coil ? If’so don’t keep it for your transmitting set (we have no licenses yet), but use the secondary wire to make transformers for , I high and low frequency circuits. That’s I j what small spark coils are for. i When you buy your next lot of flash- i light cells for “B” batteries, imbed them all in wax or pitch after connecting them up. : Leave all the long lugs protruding through ■ the wax and you will have a compact 1 variable “B” battery. Do you belong to a wireless club? Do 1 you ever think that you owe it to your I fellow amateur that you have a permit? j If amateurs had not banded together wc 1 might not have heard of permits even yet. j Mixing up with other amateurs will help 1 you quite a lot. There is nothing like an , exchange of ideas to improve your knowledge of radio, so join a club now. WIRELESS IN AMERICA America is probably the most notable ex- I ample of the rapid growth of the radio I movement. The wireless amateurs in 1 America have been given a good deal of freedom right from the commencement of 1 the movement and in that country to-day i i there are now approximately a quarter of a ; million amateur receiving stations and 25,000 amateur transmitting stations. i I In most cases the latter class of private I plants use only a small power, and, con- 1 isequently, have a limited range. To over- i I come this difficulty, however, various as- ’ I sociations have been formed the members ‘ of which have organised wireless chains j and relay messages for each other, from ‘ one end of the continent to the other. s The National Amateur Wireless Associa- <• tion, which is a large organisation, includes 1 in its membership most of the leading am a- ( teurs of the country, who, in man) cases, c have progressed so far in their knowledge of c wireless as to be classed as experts. This c association maintains a chain of private I stations and relay messages for its members f free of charge. The stations included in a

the chains contain many fine wireless sets, in most cases manufactured or assembled by the amateurs, and as the equipment of many of them .includes the latest wireless patents, a single station sometimes exceeds a ranee of 1000 miles under favourable atmospheric conditions. I The radio, laws and regulations of the I United States provide that the owner of I an amateur transmitting station must obtain a license before he is allowed to operj ate if the station can be heard in another | State, and also if the station is of sufficient ■ power to cause interference with neighbour- | mg licensed stations in the receipt of signals jfrom outside the State. These regulations ; refer to wireless telephone stations as well ias to wireless telegraphic stations. Station ticenses are issued to American citizens only, 'and a station must be operated under the supervision of a person holding an operator’s : | license. This person is then responsible I j for the working of the station. There is, t I however, no fee for an operator’s license; I neither is there any charge for a station I license. j The Government licenses which are granticd to amateur stations are divided into ‘three classes, as follows:—(1) Special sta tions known as the “Z" class, which are usually permitted to send on wave lengths | up to 375 metres; (2) general amateur stations, which are permitted to use a power input of 1 kilowatt, and which must not use a wave length exceeding 200 metres; (3.1 restricted amateur stations, which are located within five nautical miles of naval radio stations, and are restricted to i kilowatt input, and which must not exceed a 200-metre wave length. Some special experimental stations, which are known as X class stations, and university radio stations, known as “Y” class, are usually allowed greater power, and the use of longer wave lengths at the discretion of the Department of Commerce. All classes of stations are expected to use the minimum ot power necessary to carry on successful communication. Any malicious interference with official stations is a severe of fence, and any incorrect, distress signal is also punishable by a heavy penalty t

Experimenters who have had two yearrf I actual experience with radio plants arc granted special licenses allowing them to i use higher-powered sets and to transmit on : a longer wave length than ordinary amateur • stations. This class of license is, however, i granted only in cases where it can be | proved that the maintaining of the higher!powered transmitting station will prove , beneficial to cither commerce or science, and is not issued where individual amuse ment is the sole reason for the application. Any station on or near a sea coast which is granted a special license must be opera ted by a person holding a commercial license. Special licenses are issued to radio clubs if they are incorporated, or if any member holding an amateur operator’s license will accept the responsibility for the working of the apparatus. I No license of any kind is needed for the j maintaining of a receiving station for either ( telegraphic of telephonic messages, but all persons are bound by law to keep secret any message which may be overheard. No fees are charged for either an operator’s license or a station license. A 1,000 kilowatt vacuum tube, fifty times more powerful than any now in use, has been developed by the General Electric Company of U.S.A. The tube weighs sixty pounds and will Supply energy equivalent to that required to light forty thousand 25 watt incandescent lamps or enough to light 1,500 homes. In recent tests at Rocky Point, L. 1., six 20 kilowatt tubes were used in place of the Alexanderson alternator. The signals produced by the tubes were received at Nauen, Germany, with such clearness that the receiving operators did not know tubes had been substituted for the alter nator. The new tubes are fifty times i powerful as the 20 kilowatt tubes used i this test and five times as powerful as t! alternator. .