Receiver intermodulation: Enforcing the square law

The mathematics of intermodulation (IM) generation are surveyed, and it is shown that for land mobile receivers, worst case IM is a third-order effect occurring in the first mixer. The importance of relating the IM specification to the receiver sensitivity is pointed out. RF gain reduction or elimination, selectivity at both RF and IF, and the new square law mixing devices are all mentioned as techniques used for receiver IM reduction. The new diodes and field effect transistors are examined in greater detail. Their advantages of low noise and high burnout resistance are contrasted with the problems of conversion gain and high required local oscillator power levels.