THE MAGIC SPARK.

Auckland Star, Volume LIV, Issue 147, 22 June 1923, Page 11

THE MAGIC SPARK.

WIRELESS TELEPHONY.

BOW TEE SYSTEM WORKS. A NO'-TECKNICAL OUTLDvE. JOE THE MAN IX THE STREET. (By "PHOXQS.") Instead of tie usual budget of news ud goasip, I propose this week to give, ia .as simple a sonn as possible, a description of the operation of that Barvel of the twentieth century, the wireless telephone. Necessarily, to the apert and the enthusiast, who know, &ere will be much that is missing in such i description, but they will realise that ttia.is written, not for them, but for a large, inquisitive, mystified public. There are so many quite "ignorant of the high sonnding technical terms common to tireless, who have listened in, and marvelled, and who though anxious to know low it all happens are bewildered by a Seavy scientific explanation. Perhaps "US will clear the atmosphere for them. . A singer or speaker send 3 his voice nto the microphone of a broadcasting *t This microphone U exactly similar a! operation to the transmitter into *«<*. he daily speaks or growls when an Auckland telephone. The pasting station sends through °P"«, per medium of its aerial, wireless fares which for illustration here may »c compared to the waves of the ocean. erween the crests of each wave there is infinite length, measured in metres. i« esample, the Auckland station at *°ts Hall, sends on a 265 metre wave. jL.2? travels at a speed of «o,W» miles a second it can be worked w that there are radiatinjr from Scots' £•"" waTes a * the rate of over a mil--2J? T second - On this wave or through the action of the the voice wave is imposed «4 earned. Those accustomed to *w«l Instruments know well that if a Braf"+ on a one st ringed instruct it wfll set up a vibration on the ~™. ?s* e of another instrument in to it, but will leave notes of a bT» ™ pitch ivite unaffected. In c manner, if these electrical vibrations > **? -PPa-tus that is they are r Same Wave len^th a3 rtsnTt= • ?7 eUm = on > the 7 wUI produce S ****" to those that the sound 'Ct Tf^ P ° n anotl1 " musical instmhst UU i. 1S m the a PP a ratus for receivpi"/. that de ™e which will, The ™—1- d ita wa ? int °- th e home. * ted are familiar with man 7 i^ 13 that frin ? e the Auckland ttevT. ln dt 7 and suburbs, but trivano about "the little conk r bs on " frora which *«daAo^\T he SP ° ken WOrd< ° r the «X on» v Morse al P h abet. Briefly. &n O ff3 t? ° f the receiv ing set is as ' r» •+ ac^ 2al collects waves that tt«e \?k\-" rom the overhead wire ***s^ are carried b^ a dr °p- **«*£' t " h The instrument, to cot, f a the arera S« h °™. this <t ™ " usuaU 3- se ™"d ty w°g tHe wire on to a water pipe.

p_ .--THS-DTG UP. aHfc'wirt 5 COln P ariso n that has been £io&2 it .will • tha * the instrument

can "receive" it must be in "tune" —that is, capable "of responding to vibrations of the same wave length as are being broadcasted. The set, then, in its simplest form, consists of a coil of wire, connected iritb. the aeriaL A sliding device enables any varying length of this coil to be used, the remainder being cut off from operation. In reality this is simply a plan for altering, the length of the aerial so that it will be capable of receiving a certain "wave." There is also a condenser consisting of a series of connected metal plates that are capable of being rotated between another series of connected metal plates.

To pick up measagee there must be a definite balance of inductance to capacity. In other words, if a fixed length of the coil is used and this does not take the correct wave length the difference is supplied by rotating the condenser. Thus by manipulating the length of used wire in your condenser to alter its capacity, or, more frequently by adjustments of both coil and condenser, the receiving set can be put in tune with any desired Eender and when in this condition will respond to the one wave length and to no other. To thia state there are certain exceptions, such as those cauaed by close proximity to high-power plants, such as Awanui or "Spark ,, stations. Those who have had music "crashed out" by the breaking in of the G.P.O. wireless will realise what this means. REPRODUCING THE SOUNDS. Every impulse or vibration Eent out is caught by a receiving aerial within range and carried down its earth wire. These impulses are, as we have seen, of a frequency of about a million per second and are far too rapid for recognition by the human ear. Before they can become audible they have to be, what is termed '"detected"—changed, from a current of high frequency, to an intermittent direct current that will actuate an ordinary telephone receiver vibrating at about 60CO to the second, or less. This conversion is achieved by a detector, of which there are numerous types, the commonest being the "Crystal" and the "Valve.' , Broadly speaking, the action of the valve or crystal is to allow half of the vibrating current to pass and to check the alternate half. Thus is set up a pulsating current that, led to a pair of telephone receivers, reproduces the sounds sent out by the broadcasting station.

The sounds thus received, though perhaps very faint, lose none of the quality that they actually possessed before transmission, and with a good set in a good locality, should be clear of all extraneous noises except that condition technically referred as ''"static." This is caused by atmospheric electrical disturbances, and though rare in these parts during the winter, is on occasions a source of much annoyance to the patient and painstaking dabbler in wireless. The utilisation of the loud speaker simply magnifies the faint sounds on the same principle as the telephone do&s. and this magnification can be developed to such proportions that they are audible to audiences of many thousands, even in the open air. This briefly is an outline of how it is possible for many Aucklanders to sit down and listen to entertainment provided for them by broadcasters in Wellington, Sydney, Melbourne, Dtmedin and their own town. For those who have not yet "listened in" there i= a decided fascination awaiting, while the mystery | of it all may become understandable by the above explanation. !