Patent GB-1230071-A (GB)
Inventor: DELAPALME BERNARD M
IPC: G01S1/02
Filed: 1953-05-05
Abstract: 1,230,071. Radio direction-finding. B. DELAPALME. 5 May, 1953 [6 May, 1952; 2 Feb., 1953], No. 12423/53. Heading H4D. A direction-finding radio receiver for determining the bearing of radars, the repetition rate and the carrier frequency of the pulses emitted by them and their radiation patterns, comprises two superposed pluralities of microwave-receiving antennae having all similar directivity characteristics and being adapted to receive energy in different frequency ranges in each plurality, means to mount the antennae in two fan-shaped arrays, each corresponding to a given plurality, in such relative positions that the axis of the horizontal pattern of each antenna of a given array is substantially tangential to the pattern of the adjacent antenna in the array, means permitting rotation of the antennae together about a vertical axis through at least half the angle of their pattern, a detector coupled to each of the antennµ, a first video amplifier receiving in parallel all the pulses picked up by the different antennae from a radar to be located and detected by the detectors, a variable delay circuit and a sweep generator connected to the first video amplifier, a cathode-ray tube the horizontal deflection plates of which are fed by the sweep generator, a delay line having tabs connected to each detector, a second video amplifier having its input connected to the output of the delay line and its output connected to the vertical deflection plates of the cathode-ray tube, and means to radiate energy of variable frequency in the vicinity of each antenna, whereby each pulse received from the radar to be located by two adjacent antennae of the direction-finding radio receiver initiates on one hand a sweeping cycle in the cathoderay tube and produces on the other hand two pips the position of which on the cathode-ray tube screen is characteristic of the adjacent antennµ. Referring to Fig. 1, the aerial comprises two groups each of eight receiving horns, the horns of one group being dimensioned for reception of the 10 cm. band and those of the other for the 3 cm. band. The horns may be inclined at 45 degrees so as to be capable of receiving horizontally or vertically polarized wave, and this patterns at the mid-frequency of their bands are 90 degrees wide. The horns are each connected to a crystal detector and the outputs of corresponding detectors in each group are connected by a common transmission line to the grid of one of the eight double triodes 31-38. The crystals are so connected that if the output from the 10 cm. horn is positive that from the 3 cm. horns is negative. The anodes of the upper halves of tubes 31-38 are connected in parallel to the input of a video amplifier 39 the output of which may be connected alternatively to a variable delay circuit 64 or to a saw-tooth generator 40; the generator 40 is connected to the horizontal deflection plates of a cathode-ray tube 53 and can be switched to give a scan of 20 microseconds duration on one of 20 milliseconds. A thyratron 110 may be connected to the output of amplifier 39, either directly or through the delay circuit 64, and feeds a neon lamp 111 and a loud-speaker 113 through an amplifier 112 so that the pulse repetition rate of a radar under observation may be judged approximately. The anodes of the lower halves of tubes 31-38 are connected to points on a delay line 54 one end of which is connected through an amplifier 59 to the vertical deflection plates of the cathode-ray tube 53. The total delay of line 54 is equal to the time of the slower sweep of the cathode-ray tube 53 and the presentation on the tube is similar to that shown in Fig. 4. The gain of the amplifier 59 is adjusted until the top of the larger pip 71 touches the horizontal line marked 0 and the position of the top of the smaller pipe 70 indicates the angle by which the bearing differs from the bearing indicated by pip 71. For more accurate bearings the aerial may be rotated until the two pips are of equal height and the degree of rotation measured. By rotating the aerial until one horn is aligned in the direction of the transmitter a display similar to that shown in Fig. 1 is obtained and gives a diagram of the radar transmitter antenna pattern. To determine the repetition rate of the radar, the short sweep of the cathode-ray tube is used and the position along the axis 57 at which pulses appear is noted. The variable delay circuit 64 is then switched into the circuit and the delay necessary to make the pulses re-appear in the same position is measured. The repetition frequency is the reciprocal of this delay. To measure the carrier frequency of the radar each horn is provided with a radiating element connected to one of the oscillators 100, 105 covering the 10 cm. and 3 cm. bands respectively. When the oscillator is tuned to the carrier frequency of the radar the height of the pips is suddenly increased, and it is then possible to measure the frequency to an accuracy better than 1 megacycle per second.