Patent GB-600483-A (GB)
Title: Improvements in or relating to radio direction finding installations
IPC: G01S3/08
Filed: 1945-06-07
Abstract: 600,483. Radio direction-finders. CAPLIN, F., and BAGLEY, J. H. June 7, 1945, No. 14458. [Clase 40 (vii)] In a radio direction-finder of the type wherein signals received by a plurality of directional aerials are compared upon a visual indicating means, such as a cathode-ray tube, to indicate the direction from which the signals are being received, and in which the signals are switched to pass through a channel common to all the signals, means are provided for damping some or all of the tuned circuits in the common channel during the periods of switching, so as to prevent " cross-talk " from occurring between the different sets of signals. A direction finder of the type to which the invention is applicable is illustrated in block diagram form in Fig. 1 (Prov.). The outputs from two crossed aerials are fed alternately through switch 5 to a receiver, the intermediate frequency output of which is fed through switch 9, operating in synchronism with switch 5, to narrow band-width amplifiers 10, 11 and thence to the horizontal and vertical deflecting plates respectively of a cathode-ray tube. Owing to the narrow band-width of the amplifier the modulation due to the switching is removed and two continuous waves are applied to the cathode-ray tube to produce a straight line trace, the inclination of which indicates the direction of reception. The damping means may comprise diodes shunted across tuned circuits in the R.F. and I.F. portions of the receiver and rendered momentarily conducting at the instants of switching. In one embodiment, the amplifiers 10 and 11 are replaced by frequency changers, fed from a common local oscillator and intermediate frequency filters tuned to the second intermediate frequency. In the embodiment shown in Fig. 1 (Comp.) which employs diode switching, the switches 31 and 32 corresponding to switches 5 and 9 respectively of the previous figure, the damping means comprise the diodes 60, 61. The sinuosoidal output of oscillator 46 is converted to a stepped switching wave in unit 47 from which it is applied to operate the switch 31, the aerial inputs of which are applied at N-S and E-W. The switch output is amplified by the receiver and is applied to the switch 32 which is operated by a square wave applied from unit 48. The switch output is then applied to the cathode-ray tube through the amplifying channels 50, 51. To remove the effects of the finite band-width of the transformer and tuned circuit 39, which would otherwise cause successive blocks of signals to overlap, the unit 49 applies pulses to the diodes 60, 61 to cause them to conduct during the changeover periods of the switches and so damp the circuit 39. The signal/noise ratio of the trace displayed on the cathode-ray tube is improved by applying the intermediate frequency signal through the condenser 70 to the grid of the cathode-ray tube. Also it appears that the small preset condensers used in the switch 31 form a balanced Wheatstone network with the interelectrode capacities of the diodes, thereby preventing the transmission of signals through the diodes when they are not conducting.