Patent GB-638292-A (GB)
Title: Improvements in or relating to radio direction finders
Inventor: EARP CHARLES WILLIAM
IPC: G01S3/54
Filed: 1947-03-20
Abstract: 638,292. Radio direction-finders. STANDARD TELEPHONES & CABLES, Ltd. March 20, 1947, No. 7720. [Class 40 (vii)] In a radio direction-finding system of the type comprising a plurality of circularly-arranged aerials which are cyclically coupled to the receiving circuits to obtain a signal which is phase-modulated at the frequency of cyclical coupling, means are provided for simultaneously and cyclically coupling different aerials, spaced apart a predetermined amount around the array, to respective receivers, the outputs of which are combined to derive a signal modulated by the phase-difference between the modulations of two output signals, the last-mentioned signal being phase-discriminated to derive a signal which is compared in phase with a locally-generated signal to determine the direction of arrival of the received radio signal. Since in this system the phase-modulation is obtained by a comparison of two simultaneously received signals, incoherence of phase in the received signal does not affect the operation of the system. Associated with each aerial 1 ... 12, Fig. 1, of the system are two receivers 1A, 1B ... 12A, 12B. Switching waves from the generator 13 connect the aerials cyclically to their respective receivers, it being arranged, in the example shown, that when aerial 1 is connected to receiver 1A aerial 12 is connected to receiver 12B. The connections to receivers of the "B" group similarly lag behind those to the receivers of the "A" group all around the array. The output of the "A" group is taken to an amplifier 15A, Fig. 2, and that of the "B" group to an amplifier 15B. The outputs of the two amplifiers are frequencychanged to a common intermediate frequency by means of the common local oscillator 17. The output of amplifier 18B is again frequencychanged at 19 by beating it with the output of a stable crystal oscillator 20. The frequencychanged signal is amplified at 21 and mixed at 22 with the output of amplifier 18A whereby a signal of the frequency of the oscillator 20 is applied to the amplifier 23. This signal is phase-modulated according to the difference between the modulations of the signals applied to amplifiers 15A and 15B. The output from amplifier 23 is applied to phase-discriminator 24, the output of which is amplified and is applied to the phase-comparing network 26 to which is also applied a locally-generated signal from the oscillator 13 of the frequency of cyclical connection. The phase-comparing network 26 controls the direction of the bearing line on a cathode-ray tube in accordance with the relative phases of the signals applied thereto. The phase-adjuster 27 is used to set the "zero" of the bearing scale. The direction-finder may be made to operate over a wide frequencyband, e.g. 30 mc/s. to 1 mc/s., by dividing the band into a number of sub-bands and using a different spacing in each sub-band for the simultaneously-selected pairs of aerials. Thus the system may operate with the spacing described between 10 and 30mc/s. Below 10 mc/s. the phase-modulation obtained becomes too small to provide satisfactory operation and to compensate for this aerial 12 is arranged to operate simultaneously with aerial 3, aerial 1 with aerial 4, and so on, in the sub-band 3 to 10 mc/s. In the sub-band 1 to 3 mc/s., aerials spaced five apart around the array are simultaneously used. For receiving intelligence in addition to functioning as a direction-finder the receiver comprises a detector, audio amplifier and loud-speaker 28 coupled to the intermediatefrequency amplifier 18A. Specification 594,530 is referred to.