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

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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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2fi THE I(iSAT!AX boon already mentioned. Tliis may take place with respect to residual air after evacuation or with molecules of a pas introduced after evacuation. The pas is sometimes required to produce special effects. The degree of ionization depends not only on the velocity with which the electron is moving when it strikes the pas molecule, but also on the pressure of the pas. If the gas pressure is very high it means that the molecules of the gas are very numerous and an electron may collide with one before it has attained speed sufficient to cause ionization. In this ease ionization depends on the pas itself. Tf it consists of elastic particles then it is most probable that the electron will rebound and by so doing will gain sufficient velocity to ionize at the next collision. But if the gas is composed of hard inelastic particles then the electron at the moment of impact may lose all its motion which it naturally imparts to the molecule it strikes. Energy thus imparted is radiated in the form of light, producing photo-electric effects. The “Characteristic curve” of a tube is a plotted graph indicating the strength of the electron flow with various plate potential values. Theoretically it appears similar to a rather straight figure S. Its curved ends are not very pronounced. The point along this curve where the tube functions best is called the “critical point.” This is not a constant but it changes with every individual tube and with the type of work being done. The critical point is usually situated on the lower half of the S just where the curve starts to straighten out. Ionization greatly influences the characteristic. The gas molecules, being split by bombardment, result in more dislodged charges so that the current may be increased. Resulting positive ions cause, by their presence in the negative space charge, a reduction of the charge and an increase in current passed. The life of the tube may be shortened under some conditions by the bombardment of the filament by positive ions produced by collision. This causes an increase in temperature and saturation current and a consequent wear-

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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-