OVERVIEW

The probability of detecting a signal depends upon many factors in the passive DF receiver system. There are the obvious necessities of being tuned to the intercept frequency, to having the intercepting antenna pointing to the intercept, and having sufficient intercept sensitivity to ensure reception of the target signal down into its back lobes to remove the target scan effectively, if possible. If the antennas are rotating and sensitivities are limited, a "beam-on-beam" condition, where both antennas must point in each other's direction, may be the only time intercept is accomplished. If pulses are transmitted, the receiver must be ready when the target is transmitting. Since these conditions prevail for each intercept, it becomes obvious that the control and setting, or adaptability of the passive DF system, are the major factors in successful measurement of threat parameters, especially in dense environments.

To ensure proper operation of complex receiving systems, the concept of computer control immediately suggests itself and indeed is the method most commonly used. This idea has been rapidly advanced by the availability of faster and better digital devices and the obvious acceptance of digital methods in all areas of electronic technology. It has also been advanced for passive direction finding by the use that is made of this information. Since passive DF data derived for threat detection is used for protection, decision making, and control of countermeasure assets, the idea of "power-managed" defensive countermeasures has evolved as the optimum way to direct protective assets to counter priority...