Investigation of Resonance Curve with Respect to Variation of Capacity

Abstract

An investigation of the possibility of using a vibrating variable condenser in a Hartley Oscillatory circuit to modulate the radiofrequency of the circuit, and a study of the effect of u,sing the same type of condenser in a receiving circuit to modulate its radio frequency. Introduction This paper is the result of a piece of work started in September, 1930, by Professor Lyon and the writer at K. S. 'C. The work is still being carried on. In the revised edition of the Radio Manual by Sterling which came out about one year ago this same problem under the heading of Frequency Modlulation is suggested with a method of procedure. Efforts to find out from the author or editor what work has been done on the subject so far have failed. This article did not reach us until this spring when a revised edition of the Manual was received. So this work was completed independent of all others. At the present time the vacuum tube is the only means of modulation and amplification that has proved successful for work in radio telephony. With this in mind, it was decided to investigate the possibilities of a mechanical modulator operating by small variation of capacity in one of two coupled radio circuits. When the three-electrode vacuum tube is used as an amplifier and the plate current is plotted as ordinates against the grid voltage, a characteristic curve is obtained. The usefuj, portion of this curve lies between the points a. and b. Figure 1. The resonance curve obtained by plotting the current against the capacity in an oscillating circuit of very low resistance, bears a certain resemblance to the tube characteristic of Fig. 1. When one-half of this resonance curve is compared with that of the useful portion of the tube curve, it is seen that they are very similar. This suggests the possibility of placing a vibrating condenser in the circuit of an oscillator and obtaining effects of modulation and amplification analogous to those ordinarily obtained with the use of a tube. In other words, the construction of a mechanical modulator and, in some cases, amplifier, to replace the vacuum tube. The object of this work was to determine (1) what effect a vibrating condenser, placed in a receiving circuit coupled with an osThis content downloaded from 157.55.39.163 on Wed, 23 Nov 2016 04:26:51 UTC All use subject to http://about.jstor.org/terms