Off-channel frequency discriminator circuit for use in a precision distance measuring equipment (DME/P) receiver

摘要

A precision distance measuring equipment (DME/P) receiver for detecting an RF signal including at least one interrogation pulse is described. The DME/P receiver includes first and second signal processing channels. The first processing channel includes a wideband filter, of bandwidth BW1, for receiving the processed RF signal and in response thereto generating a wideband (FA) mode signal proportional to the logarithm thereof. The second signal processing channel includes a narrowband filter, of bandwidth BW2, for receiving the processed RF signal and in response thereto generating a narrowband (IA) mode signal proportional to the logarithm thereof, the bandwidth BW2 of the narrowband filter being within the bandwidth BW1 of the wideband filter. A frequency discriminator circuit receives samples of the FA and IA mode signals from the first and second signal processing channels, and in response thereto generates a control signal when the pulse has a frequency within the bandwidth BW1 but outside the bandwidth BW2, the control signal representing an "off-channel" condition. In operation, gating circuits are connected to receive the control signal from the frequency discriminator circuit and operate to inhibit further processing of the FA and IA mode signals in the receiver during the "off-channel" condition.