Patent GB-761267-A (GB)
Title: Improved direction finder
IPC: G01S1/02
Filed: 1954-03-15
Abstract: 761,267. Radio direction finding. WAECHTLER, M. March 15, 1954 [March 23, 1953; March 24, 1953; April 29, 1953; May 5,1953; May 5, 1953], No. 7396/54. Class 40(7) In a direction finder of the type having crossed loop or Adcock type aerials and an auxiliary aerial for sense determination, which has two amplifier channels coupled to a cathode ray tube indicator provided with a rotatable cursor for reading bearings, means are provided to enable sense determination to be effected by feeding the auxiliary aerial signals through one or both of the said amplifier channels. In a first embodiment the crossed loop aerials are connected at 1 and 2 and each loop feeds through its respective amplifier channel 3 or 4 to influence the deflecting systems of the cathode ray tube indicator 7 the resultant indication is a line trace 9 passing through the centre of the tube. A rotatable cursor, which may have a. number of parallel lines engraved on it, may be manually aligned with the trace and the bearing read off on scale 12. To resolve the 180 degrees ambiguity of the system so far described signals from auxiliary aerial 17, adjusted in phase at 18a, are fed through switch 25 to the search coil of the goniometer 15. The field coils of the goniometer are connected one to each amplifier channel 3 and 4 and the search coil is positioned by mechanical linkage 20, 21, 22 in accordance with the position of the cursor. Operation of switch 25 reverses the phase of the signals applied to the goniometer and in one position of the switch the trace 9 is longer than in the other. The switch positions are colour coded as by markings 23<SP>1</SP>, 24<SP>1</SP> and corresponding coloured markings 23 and 24 are provided on the cursor. The correct unambiguous bearing is that read off from the end of the cursor having the same colour marking as the switch position corresponding to the longer trace. In a second embodiment (Fig. 3), the loop aerials 31, 32, are conected by switch 33 through channels 36, 37 to the deflection systems 58, 56, of cathode ray tube 38 to produce an ambiguous bearing trace 55. The indicating cursor is aligned with the trace as in the previous embodiment and is coupled to position the search coil 41 of a goniometer. To resolve the ambiguity lever 54, operating switches 33, 46, and 50, is put in the sense determination position. The loop aerials are then coupled to the respective field coils of the goniometer and the goniometer output fed through channel 36 to deflection system 58. The auxiliary aerial 48 is, at the same time, connected through a phasing device and over switch 46 to channel 37. The output of the channel is fed to control the intensity of the cathode ray tube beam at connection 57. The sense determination position produces a linear radial indication in one direction or the other from the centre of the tube along the line corresponding to deflection system 58. The direction of the trace indicates which end of the cursor should be read for the unambiguous bearing. In a third embodiment (Fig. 5), the loop aerials 61, 62 feed through channels 65, 66 to produce the ambiguous bearing indication which can be read off by means of the cursor and scale 67. For sense determination switch 76 is moved to couple auxiliary aerial 61a through phasing arrangement 75 to the input of one of the channels. This has the effect of turning the figure of eight pattern of the corresponding loop into a cardioid pattern and the bearing scale is compressed into a 180 degrees scale as shown at 71. The resultant indication on this scale is unambiguous and shows which of the more accurate readings should be taken. Operation of the switch 76 may be ganged with mechanical or electrical means for changing the scale visible round the indicator tube. In the first two embodiments described switches may be incorporated to couple the loop aerials to the goniometer field coils and the search coil through one amplifier channel to an audible device so that bearings can also be determined by the aural null method. Any direction finder according to the invention may be further provided with a, switch having a " calibration " position between the " off and the direction finding position. In this switch position equal test signals are applied to the two amplifier channels and should produce a straight line at 45 degrees. If this is not the case preliminary adjustment of amplification and/or phase shift is necesssary. Preferably the tuning and means for correcting the channel amplification and phase shift are effective only in the " calibration " switch position. Further a photocell device may be provided which, if the calibration has not been correctly carried out to produce a line at 45 degrees, prevents the switch being moved to the direction finding position or effects the disappearance of the trace or bearing scale if the switch is so moved.