Abstract: This invention relates to a system to alert an aircraft pilot of the presence and general location of other aircraft that might constitute a collision threat to the pilot's aircraft. A first and second antenna on the upper paid lower surfaces of the aircraft each operate in first and second modes characterized by respective first and second directivity conditions. The first and second antennas directly receive pulse signals from a source in order to determine the relative time of arrivals and thus the relative altitude of the source to the aircraft. Analysis means compares amplitudes of responses in the first and second modes to provide an angle indicating signal without having to generate radio signals other than those already being generated by equipment in the other aircraft in response to ground ATC interrogation.

Abstract: Radio signals containing Loran C pulses from stations from a desired chain are amplified, filtered and ensembled averaged in an acquisition memory which is accessible by a controlling microprocessor. By staggering the ensemble averaging of the first four pulses in a station pulse group in time with respect to the last four pulses of the same pulse group, cross correlating the composite pulses formed by averaging the first four and last four pulses of the station pulse group with the help of the microprocessor provides time skew information which is used to adjust the receiver's master clock to align it with the clock of the transmitter. By varying the amount of time stagger, an ever finer resolution adjustment range is achieved. When the staggered averaging cycle times would exceed the time between successive ensemble averaging cycles without stagger, then successive ensemble averaging cycle time is employed for master clock adjustment.