Patent GB-570204-A (GB)
Title: Improvements in radio direction finders
IPC: G01S3/14
Filed: 1942-02-04
Abstract: 570,204. Wireless direction-finding systems. ROOYEN, L. J. VAN, and AGAR, W. O. Feb. 4, 1942, No. 1502. [Class 40 (v)] A radio direction-finder, of the kind in which the signals in two channels fed by two mutuallyperpendicular aerial receiving systems are applied to corresponding mutually perpendicular deflecting members of a cathode-ray indicator, is provided with a brilliancy-controlling circuit operated by the detected combined output from the two channels and having variable delay constants, by adjusting which the trace on the screen may be made to correspond to a component of the signal arriving at a desired time after its commencement. In this way the indication may be produced only by the component ray of the signal arriving in a direction indicating the correct bearing. This' ray may not be the first to arrive, owing to the ionospheric conditions, and in such cases transient conditions occurring during the arrival of the ray are used in the operation of the system. In the system shown in Fig. 1, signals which, owing to the successive arrival of rays travelling by different paths, each have a form such as that indicated at g, Fig. 2, are supplied from mutually - perpendicular aerial systems to oscillator and mixer units SC1, SC2, the intermediate frequency outputs of which are applied to filter-amplifiers FA1, FA2 which pass only the transient components to the X and Y deflecting systems of a cathode-ray indicator CRO1, giving_a straight-line trace, the inclination of which depends on the relative amplitudes of the two outputs. The outputs from SC1 and SC2 are also applied to selective buffer amplifiers BA1, BA2, the combined outputs of which are passed to an amplifier detector AD, the output a from which has a stepped form corresponding to the integration of the three rays arriving as shown at g. The output from AD is applied to a trip circuit TC1 which when the signal output rises above a certain level, at a time t<1>, produces an impulse c which causes a brilliancy control circuit BM to emit, after an adjustable time-delay, a pulse d. This pulse causes the traee on the screen of CRO1 to appear, or to increase in brilliancy, only during reception of the desired component of the signal, in the case shown the second to arrive. The system shown is provided with a monitoring cathode-ray indicator CRO2 which shows a trace of the complete signal in which the portion selected to provide the indication on CRO1 appears at greater brilliancy than the remainder. For this purpose a second trip circuit TC2 connected to the amplifier detector AD emits a delayed pulse e at a time t<11> subsequent to t<1> and trips an aperiodic time-base circuit TB connected to the Y deflecting system of CRO2. The output of AD is applied to the X deflecting system of CRO2 through a circuit DC1 giving a delay such that the output b commences at a time t<111>. The output of the control circuit BM is applied through a unit DC2 giving the same delay as DC1 to produce an impulse f which is applied to the brilliancy control electrode of CRO2, so causing an increase of brilliancy of that part of the trace representing the selected compound of the signal. The trip circuit TC2 ignores signals of short duration and cannot operate again until the detector output has been reduced below the predetermined level for a certain time. When the first ray to arrive is to be used, the brilliancy control circuit is adjusted so that the indication in the tube CRO1 only when the steady-state component h, due to the first ray is being applied to it. In this case, the filters FA1, FA2 are omitted, since transients are not employed.