Navigation receiver with doppler filter gating

In a Doppler type radio navigation receiving system arranged to be responsive to a radio beacon transmitting a main angle data signal produced through successively scanning by commutating a radio frequency source to the radiating elements of a linear array according to a predetermined switching directional program and a transmitted reference signal at a frequency offset from the frequency of said radio frequency source, said beacon being arranged to digitize the scan program of said array, the combination comprising:

• first means within said receiving system for deriving a Doppler beat information signal from said main and reference beacon signals;
• a bandpass filter connected to receive said beat signal from said first means, said filter pass band substantially covering the frequency range of said information signal corresponding to said main angle data signals arriving at said receiver by direct path;
• frequency measurement means responsive to the output of said bandpass filter for determining the frequency of said beat signal;
• synchronizing means responsive to at least one of said main and reference signals, generating a gating period for controlling the time of response of said frequency measurement means to produce an output therefrom for a time during each of said scan cycles which is less than the period of the full corresponding scan cycle.