Abstract: A range processor for airborne distance measuring equipment in which coherency of reply signals from the ground based DME station is determined by incrementing the contents of storage locations of a random access memory device for each reply signal according to the time of reception of the reply signal and for decrementing the contents of the storage location if no reply signal is received. Whenever the contents of a storage location exceeds a threshold value a range gate is generated so that the next reply received within the range gate causes the time of reception of the reply to be stored as range data.

Abstract: A video processor for Distance Measuring Equipment in which all timing functions including fixed delays are performed by digital counters counting clock pulses from a highly stable source. Search and track operations are conducted by starting a memory counter by a reply from a responser and stopping the memory counter at a time corresponding to maximum range. On a succeeding interrogation cycle the memory counter is started prior to the time a reply at zero range would be received. In this cycle the memory counter begins count with the count it contained when stopped during the previous cycle; the memory counter counts until it reaches a number corresponding to maximum range, stops and initiates a range gate. A reply within the range gate causes the range gate to be repeated at the same time in the following interrogation cycle. A sufficient number of replies within the range gate cause tracking operation to begin. A velocity memory provides continuing tracking during temporary loss of reply signals.

Abstract: Combined keyed AGC and pulse amplitude comparison circuit for use in pulse pair communications system such as DME wherein AGC keying signal is constituted by the second pulse having a predetermined spacing from a first pulse of a pair and wherein said second pulse also provides a reference against which the amplitude of succeeding pulses is compared. Pulses with amplitudes above said reference level are passed to a decoder for determining pulse spacing. The decoder determines which pulse pairs are properly spaced so that the second pulse of a pair can serve as a keying signal.