Automatic recording of the direction of arrival of radio waves reflected from the ionosphere

Equipment is described which, for a fixed frequency, simultaneously determines the direction of arrival of all resolved pulses reflected from the ionosphere by measuring the phase differences for two pairs of fixed orthogonal spaced-loop aerials. The vector sum and difference of the signals for each pair of loops in turn are formed in a special unit. These are amplified in normal receivers and the rectified video outputs applied to the Y-and X-plates respectively of a cathode-ray tube. The orientations of the resulting lines are thus governed by the phase differences between the signals at the pairs of loops. Pulse resolution is achieved by the simultaneous application of a time-base in the X-direction. Phase-balanced receivers are not required; since the phase-sensitive portion of the equipment is confined to the loops, pre-amplifiers and the sum-and-difference unit, the system is stable enough to run without attention for up to one week.