Aircraft landing radio guidance receiver which warns of signal reflections

Claim 1

Receiver apparatus for use in an aircraft landing radio guidance system of the type which provides two double-sideband guidance signals, the relative amplitudes of which are intended to be a measure of the position of a receiver relative to a preferred approach path; the said apparatus comprising: receiver means for receiving the two double-sideband guidance signals of the radio guidance system, sideband filter means connected to the receiver means, for separating the upper-sideband components of the said guidance signals from the lower-sideband components of the said guidance signals, a first signal multiplier means connected to receive the said upper-sideband components from the sideband filter means, for deriving beat-frequency signals from the said upper-sideband components, a second signal multiplier means connected to receive the said lower-sideband components from the sideband filter means, for deriving beat-frequency signals from the said lower-sideband components, and comparison means, connected to the first signal multiplier means and the second signal multiplier means, for comparing the upper-sideband beat-frequency signals with the lower-sideband beat-frequency signals and indicating a discrepancy between them.