University of San Francisco - USF Don Yearbook (San Francisco, CA)

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28 TIIE IGXATIAX frequency would make absolutely no impression on the phones. A conversion is necessary to render the transmitted wave audible. These audio frequency currents are not necessarily direct currents in the strict sense of the word. They may be groups of separate direct current impulses but it does not make much difference provided that they affect the diaphragm of the phone under about fifteen hundred impulses a second. There are two general systems of wireless transmission— the continuous wave or C. Y. as it is called in the parlance of the profession, which sets in motion waves of continuous amplitude and undamped oscillation. These are of radio frequency. The discontinuous wave consists of oscillations which are not continuous in their passage through the ether. Furthermore the amplitude of the oscillations are not constant. Instead, after such waves have been given their initial start by the first power stroke of the transmitter, they rise to sudden height and gradually fall lower and lower in amplitude until they are finally damped out completely. The next stroke of the transmitter causes them to rise again and the rising and falling process keeps up indefinitely, depending on the amount of energy in back of it. Thus this sort of discontinuous or damped wave, as it is technically called, travels through space till it is exhausted; likewise its carrying powers are entirely proportionate to its initial energy. It is produced by the spark type of transmitter and has been in use since the inception of wireless communication Another phase of C. AA transmission is what is known as I. C. Y. or Interrupted Continuous 'Wave. I. C. Y. is practically the same form as C. AY. with the exception that an interrupter is inserted in the radiating circuit of the transmitter to break up the emitted waves so that they will be heard as universal audible tones at the receiving end; otherwise a special receiving circuit must be employed to render the waves audible as is done in C. AY. work. Damped and T. C. AV. waves may be detected by the ordinary detector and require no special hook-up for reception. Even a coherer or a mi-

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THREE ELEMEST VACU UM TURK 27 ing away of the filament. Sometimes when ionization takes place positive ions at the surface of the filament combine with electrons forming a blanket of gas around it thus paralyzing the tube. The common saying was, a few years ago. to have a tube “go dead on you ' This meant that while in operation the gas formed effectually insulating the filament. The remedy for this paralysis is a slight overheating of the filament or an entire cessation of operation for a few minutes. There is no danger of paralysis when using a lube that has been thoroughly evacuated. Applications of tiik Three Electrode Vacitm Ti de Since the time when Marconi perfected the Wireless Telegraph. many of the greatest geniuses of science have been at work elaborating, improving and finishing every detail and phase of the original discovery. Hertz had discovered that the waves were transmitted through the ether so the problem was to invent an ultra-sensitive detector which would make known their presence, no matter how weak they might be. The solution of this problem was found in the Vacuum Tube which acts as a most sensitive detector, in fact the most sensitive detector of these waves yet discovered. This is but one application of the Vacuum Tube in Wireless. It may be also used as an amplifier either in conjunction with other tubes or by itself alone. The radio-phone would not exist if it were not for the Vacuum Tube functioning as an oscillation generator. A radio-wave is defined as a vibration through space. These waves range in frequency from the audible to the inaudible. Currents having a frequency of ten thousand cycles per second or over are termed currents of radio frequency and those of cycles under this figure are audible when rectified and are called audio-frequency. The usual wave-length of amateur stations in the United States is two hundred meters and the wave has a frequency, sometimes, of one million five hundred thousand cycles per second. This high

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THREE E LEM EXT YAC1TM TV BE 20 crophonic detector might be used for these types of waves but tlie same does not hold for continuous waves which are damped and which make no impression on any detector except at the beginning and end of such a wave and even then it is only evidenced by a click. When the crystal detector was in vogue it was customary to use some sort of mechanical interrupter in the circuit which was called a tikkcr. This tikker broke up the incoming continuous wave some three hundred to one thousand times a second, thus rendering the wave, when rectified, audible. This method was popular because there was no other. At the best it was crude and could be no better than the crystal detector that was used with it. The advent of the Vacuum Tube caused a hundred per cent improvement in both the detection of damped and undamped waves and in the method of rendering the 0. Y. audible after detection. The Vacuum Tube method entirely supplanted the old “Tikker” method. The system by which the ( AY. is rendered audible is sometimes referred to as “Beat reception” but is more properly called “Heterodyne.” The desired effect is obtained in the Vacuum Tube by supplementing the incoming radio frequency wave with a locally generated current which differs in amplitude by an amount which lies within the range of audibility. The resulting fortification and interference which takes place due to periodic synchronism gives rise to a third or “beat current” which, when properly rectified is audible. In this case as in detection the input is a trifle greater than the output due to the addition of the incoming wave to that locally generated by the tube. A brief account of the two methods, by which damped oscillations may be detected, follows: (1) The grid current is maintained with respect to the cathode, so that a negative grid charge will be followed by a slight decrease in the anode current or a positive charge on the grid will produce a relatively high increase in the plate current and the receivers are affected once for each