Patent ID: 7683823

Claim:
A DME ground apparatus comprising: an aerial unit that receives an interrogation signal from an aircraft; a transponder unit that receives the interrogation signal from the aerial unit, generates a response signal in response to the interrogation signal and transmits the response signal to the aircraft; and a monitor control unit that monitors and controls the transponder unit, wherein the transponder unit includes, a circulator that isolates, separates, or couples a received signal, an IF converting unit that converts an output of the circulator to an IF-band signal, an analog-to-digital converting unit that AD-converts and digitizes the IF-band signal from the IF converting unit, a processing unit that calculates, from a digital signal digitized by the analog-to-digital converting unit, three detected outputs including a center frequency of the digital signal and frequencies that are ±900 kHz deviated with respect to the center frequency, and compares and determines the magnitude of the calculated three detected outputs, and a pulse transmitting unit that transmits a pulse of a response signal in accordance with a result determined by the processing unit, the transponder unit calculates detected outputs of a center frequency of a received interrogation signal, and two frequencies that are ±900 kHz deviated with respect to the center frequency, determines, when the detected output of the center frequency is larger than the detected outputs whose frequencies are ±900 kHz deviated with respect to the center frequency, a received signal as a desired signal and transmits a response signal to the aircraft, and determines, when the detected output of the center frequency is smaller than the detected outputs whose frequencies are ±900 kHz deviated with respect to the center frequency, a received signal as a signal of an adjacent channel and does not transmit a response signal to the aircraft.