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 Oscillator circuit to modulate the radio-frequency of the circuit, and a study of the effect of using the same type of condenser in a receiving circuit to modulate its radio-frequency. A receiving set in the form of a wave meter containing a variable condenser that may be made to vibrate at voice frequency is coupled inductively to a Hartley Oscillator and tuned to its frequency. It is found that the current in the wave meter fluctuates with the capacity change and that This shows that the effective current in an oscillatory circuit of extremely low resistance and operating near the peak of the resonance curve, may be controlled by the application of an audio-frequency variation of capacity. These results are, in form, very similar to those obtained with respect to the characteristic curve of a vacuum tube when changing the grid voltage. This makes 3 possible a system of modulation in which the radio-frequency changes according to the action of an audio-frequency control, but without change of amplitude, and without direct observance of the usual heterodyning rules of audio and radio frequencies. It is different from the ordinary type of modulation in which the audio-frequency is impressed upon the carrier wave as an envelope of the amplitude of the latter, and with the ordinary heterodyning rule of the addition and subtraction of the audio and radio frequencies.