The Sideband Intermediate Frequency Radio Communications System

A communications system is described which eliminates oscillator-frequency drift problems by incorporating an amplitude modulated transmitter modulated by an oscillator tuned to half the intermediate frequency of the receiver. The use of a balance modulator elimates the carrier and allows energy at the two sideband frequencies to be propagated to a receiver. In the receiver these two sidebands are beat against each other to produce the IF signal. No receiver local oscillator is required. Only one high-frequency oscillator, the transmitter carrier oscillator, is used in the entire system, and frequency drift problems are reduced to those of low-frequency oscillators. However, preliminary investigation indicates that a bandwidth of twice that of a regular communications system is required in most cases. The system may prove useful at frequencies between the microwave and infrared regions.