Patent GB-594710-A (GB)
Title: Improvement in pulse radio direction finder system
IPC: G01S1/02
Filed: 1944-12-29
Abstract: 594,710. Radio direction-finding. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Dec. 29, 1944, No. 26151. Convention date, Dec. 30, 1943. [Class 40 (v)] [Also in Group XXXVI] In a pulse receiver with a cathode-ray tube indicator suitable for use in pulse directionfinding systems, vertically displaced forward and fly-back time-base sweeps of adjustable phase with respect to the received pulses are produced by applying a saw-tooth wave with a slowly increasing component and a rapidly decreasing component to the horizontal deflection systems of the cathode-ray tube and producing pulses of the same duration as one of the components of the saw-tooth which are applied to one vertical deflection system of the indicator, the received pulses being applied to the other vertical deflection system. The invention is described as applied to a pulse direction-finder designed to obtain the bearing of any one of a number of pulse transmitters operating at the same frequency, the transmitters being grouped in pairs with a different pulse-recurrence frequency for each pair. As shown in Fig. 1, the sine wave output 30 from the oscillator 28 is shaped by the valves 31 and 32 to give a square wave 34 which is differentiated in the R.C. circuit 37, 36 to give a peaky wave 38, the positive peaks of which render valve 41 conductive, thus rapidly charging condenser 43 in the cathode circuit. The rising cathode potential cuts off valve 41 and condenser 43 discharges slowly through resistance 21 giving a saw-tooth waveform 17 which is applied in push-pull through valves 18 and 19 to the horizontal deflection plates 16, 16a of the cathode-ray tube 14. The negative pulses 46 developed in the anode circuit of valve 41 are inverted and limited by valve 48 and applied to the vertical deflection plate 13a to separate the slow sweep 26 from the fly-back sweep 27. The square wave from valve 32 is also applied to valve 48 through the small condenser 55 which differentiates it to give a small peaky waveform, the negative peak of which produces a small positive pulse in the anode circuit of valve 48 half-way between the larger pulses 23 and this small pulse produces a centre mark 71, Fig. 9, in the slow sweep 26. The radio pulses received by the rotatable loop im the streamlined housing 10 are applied through the receiver 11 and detector 12 to the vertical deflection plate 13. To operate on a particular pair of transmitters, the switch 29 on oscillator 28 is set to the appropriate recurrence frequency and the fine recurrencefrequency control 73 is set to make the pulses stationary on the slow sweep 26, Fig. 9 ; the control 73 is then adjusted to shift the pulses on to the fast sweep 27 when the direct pulse A can be distinguished from the indirect pulses A', A<11> reflected from the ionosphere, thus enabling an accurate D.F. to be carried out on the direct pulse. If the pulses from a given pair of transmitters A, B are radiated in the sequence shown in Fig. 10, they may be identified by aligning 'one pulse with the beginning of the slow sweep ; if the slow sweep runs from left to right and the second pulse is to the right of the centre mark 71, it is a B pulse, Fig. 10a, but if it is to the left of the mark it is an A pulse, Fig. 10b. The oscillator 28 as shown in Fig. 2 comprises a two-stage R.C. coupled oscillator in which positive feedback is applied from the output of valve 52 to the input of valve 51 through the coupling condenser 54 and the frequency selective network comprising resistances 56, 57, condenser 58, resistances 61, 62 and 63 and condenser 64 which is shunted by the condensers 64a &c. selected by the frequency control switch 29 and by the variable condenser 64<1> operated by the fine frequency control 73. The amplitude of the output taken from the cathode circuit of valve 52 is maintained constant by applying negative feedback from the anode of valve 52 to the cathode of valve 51 along the path comprising resistance 68 and the tungsten-filament lamp 67.