The Application of Negative Feedback to Frequency-Modulation Systems

H I S paper describes a method for improving the performance of receivers designed to receive frequency-modulated waves. In its broader aspects this method can be described as the application of the principle of negative feedback to a superheterodyne frequencymodulation receiver. In its details the application of the feedback principle necessitates the use of a rather unusual circuit arrangement. This circuit differs from that of the simple feedback system in that the voltages fed back are not of the same frequency as those applied * Presented before N e w Y o r k Section of I. R. E . , M a y 3, 1939. Proceedings, I. R. E., M a y 1939. Published in 404 NEGA TIVE FEEDBA CK 405 to the input of the receiver, and are caused to influence the response of the system by modifying the performance of the modulator. In the ordinary feedback amplifier a part of the output voltage is carried back to the input and there combined with the applied voltage. The result is to modify the output and if the gain of the system is thereby reduced the feedback is said to be negative. The many advantages which result from negative feedback have been described by Black 1 and are coming to be more generally appreciated. The present paper deals with a method for adapting this principle to a frequencymodulation receiver and will show an example of its application to an experimental system in the laboratory. GENERAL DISCUSSION