The Interference Noise in High-Quality Push-Pull Frequency Modulators

There exists a special kind of loading noise in highly linear push-pull frequency modulators used in radio links. It is caused by the higher order interference products in the mixer of the modulator. This noise can be very annoying and necessitates a careful selection of the oscillator frequencies. The theory leading to optimum frequencies is shown, and equations for the direct calculation of the baseband-interference loading noise are given. Reference is made to experimental results.