Abstract: A radio system for determining the range and bearing of mobile equipment, such as an aircraft, relative to reference equipment such as an aircraft carrier, with low probability of interception (LPI). The aircraft remains equipped with high power range and bearing determination equipment, such as TACAN equipment. Reference equipment transmits a LPI beacon, such as a pseudo noise code spread spectrum signal through a rotating beam antenna to amplitude modulate the beacon as a function of antenna orientation. The PN code is inverted as the antenna passes through a reference bearing. Mobile LPI equipment determines bearing and generates a high power signal, such as an emulated TACAN beacon signal. High power range and bearing equipment extracts bearing information from the emulated signal and display it. Range can be determined in a cooperative mode. Mobile LPI equipment transmits a LPI interrogation signal. Reference LPI equipment returns a LPI reply signal.

Abstract: A signal processing means and method of adaptively filtering input signals received at a terminal means in which the input signals include pulse signals and noise, with the pulse signals occurring at unknown times and having unknown durations, which includes signal filtering means having a first input for receiving signals derived from the terminal means, a second input and an output, the signal filtering means having a controllable filter characteristic for passing signals from its first input to its output responsive to signals received at its second input, and a signal analyzing means having an input receiving signals derived from said terminal means and an output delivering signals which are responsive to signals received at its input, to the second input of said signal filtering means for controlling its filter characteristic, whereby the output of the signal filtering means delivers signals corresponding to the pulse signals of the input signals to said terminal means while minimizing delivery of noise