Abstract: A method of analysing clusters of bearings (A, B, C, D) taken of distant sources by an array of direction finding stations. Each bearing has an error +E and a triangulation process is used to fix the position of the sources. A combination of bearings is taken one each from the stations. Each bearing of the combination is taken in turn as a spoke (3) directed at a source. The triangulation process generates a bar (31, 32, 33) of intersection points along the spoke for each other bearing of the combination, each bar corresponding to the error +E of each bearing. The number of overlaps between pairs of bars along a spoke is totalled to give a spoke score. The spoke scores of all spokes of the combination is summed to form a fix confidence score for a source which may be associated with the combination, or cluster, of bearings. Methods are also provided for rejecting redundant fixes associated with subsets of bearings within a cluster.

Abstract: A system for amplifying R.F. signals with a selectable substantially constant phase at the output port (OP) relative to the input port (IP) comprises a phase shifter (PS) and an amplifier (AMP), a phase discriminator (PD) and a video processor (VP) which controls the phase shifter (PS) in accordance with the output of the phase discriminator (PD) and a phase selection signal (SEL). This signal (SEL) selects a bias voltage to cause the phase shifter to introduce a phase shift such that the relative phase at the output port is approximately equal to a desired value and also to select a monotonically varying error function which is derived from the phase discriminator and which is representative of the difference between the desired value and the actual value of the relative phase.

Abstract: Angular ambiguity, particularly in measurements made in radio interferometers, is resolved by comparing an ambiguous value for a desired angle with an unambiguous value for an angle which is ideally equal to the desired angle but which may differ from it by an error angle less than .pi.. For example, ambiguity in the phase difference between a pair of widely-spaced antennas may be resolved by reference to the sum of two unambiguous phase differences between each of those antennas and an intermediate antenna. The effect on the ambiguity-resolution process of certain sources of phase errors in practical systems can be eliminated, leaving a large tolerance to remaining errors.