| 摘要 |
<p>In distance measuring equipment (DME) for use in aircraft an interrogation is transmitted from a local airborne DME, generally to a ground station. The transmitted signal is also sampled and transformed by a local oscillator means to the frequency of the expected response and applied to the front end of the DME receiver. The sampled and transformed signal thereafter traverses the receiver circuits and is applied to start a range clock at the rear end of the receiver. Simultaneously, the signal traversing the receiver circuits is sampled and memorized in a sample and hold circuit. A response to the interrogation, when received, is also applied to the front end of the receiver and traverses the receiver circuits and applied to stop the range clock, the resulting change of state of the range clock being related to the range between the interrogating and responding stations. The response signal traversing the receiver circuits is sampled and memorized in a second sample and hold circuit, with the contents of both sample and hold circuits being compared against one another. The results of the comparison are applied to the local oscillator means to control the amplitude of the output signal thereof.</p> |
