Patent GB-599602-A (GB)
Title: Means for exact reading of the phase position of an arbitrary impulse in a periodically recurrent series of impulses
IPC: G01S1/02
Filed: 1945-10-16
Abstract: 599,602. Radiolocation. SVENSKA AEROPLAN AKTIEBOLAGET, and AKTIEBOLAGET BOFORS. Oct. 16, 1945, No. 27079. Convention date, July 29, 1944. [Class 40 (v)] [Also in Groups XXXV and XXXVI] Relates to means for determining the phase of a train of signal pulses of a wave nature having a recurrence frequency (P.R.F.) fi with respect to a reference oscillation of the same frequency, in which the signal pulses are applied to a normally blocked gate valve which is periodically renderedconductive by a train of gating pulses adjustable in phase with respect to the reference oscillation. According to the invention, the phase of the gating pulses is periodically shifted at a frequency lower than that of the recurrence frequency and the average phase of the gating pulses is adjusted so that the amplitudes of the signal pulses passed by the gate valve in its two conductive conditions is equal, which condition obtains when a signal pulse is located symmetrically between two corresponding gating pulses. Means are also described for automatically maintaining this condition independent of further variations in the phase of the signal pulses. The invention is described as applied to pulse echo ranging systems in which the phase of the echo pulse with respect to the transmitted pulse is a measure of the range. In the radar system shown in Fig. 2, the transmitter component of the transmitterreceiver I is synchronized by the 10 kc/s. oscillator O and the echo signals are fed from the receiver component to the gate valve V. The sinusoidal output from O is applied through a variable phase-shifter FV to a phase-switching device S, Fig. 5 (not shown), comprising a circuit tuned to the P.R.F. across which a reactance valve is connected and a 50 c/s. switching voltage Vs is applied to the valve so that the tuning is varied in successive halfcycles causing the phase of the output voltages to vary by an amount 2## as shown in Fig. 6. The output from the phase-switching device is converted into narrow pulses in the generator Ih and these are applied as gating pulses to the outer control grid of the heptode gatevalve V, Fig. 3 (not shown). If the phaseshifter is adjusted so that the echo pulse is positioned symmetrically between the alternately produced gate pulses, each gate pulse overlaps the echo pulse equally and the amplitudes of the echo pulses passed by the gate valve in its two conductive states are equal, but if the echo pulse is not symmetrically positioned then one gate pulse will overlap more than the other and the resultant echo signals will be modulated as in Fig. 8. The modulated train of wave pulses, Fig. 8, is fed to a detector D1, the output from which is applied to a circuit F1 tuned to the P.R.F. giving a modulated sinusoidal wave train, Fig. 9, which is fed to a second detector D2 giving a square waveform. Fig. 10, which is converted to a sinusoidal waveform, Fig. 11, in the circuit F2 tuned to the switching frequency. The waveform, Fig. 11, is in phase or out of phase with the switching waveform, Fig. 12, according to the sense of displacement of the echo pulse from the position of symmetry and the amplitude varies with the amount of displacement so that the condition of symmetry can be indicated by applying the two waveforms to a dynamometer-type instrument, Fig. 14 (not shown), or to a cathode-ray type indicator. Once the symmetry condition has been obtained by manual adjustment of the phase-shifter FV, it may be maintained automatically by apply-, ing the two waveforms, to a commutator motor M geared to the phase-shifter. In order to assist the selection of a particular echo, all the echo signals together with the gating pulses are displayed as deflections on a cathode-ray tube oscillator with a linear trace.