Patent GB-615417-A (GB)
Title: Improvements in radio direction-finding systems
IPC: G01S1/02
Filed: 1945-04-25
Abstract: 615,417. Radio direction-finding. SMITH, S. B., and KEMP, R. J. April 25, 1945, No. 10447. [Class 40 (vii)] A radio direction-finding system responsive to pulse transmission has an aerial system having two overlapping directional polar diagrams defining an equi-signal line and means for rendering the two polar diagrams effective in alternation at the frequency of recurrence of pulses radiated by a co-operating transmitter. The aerial system of one embodiment, Fig. 3, consists of four frame aerials mounted symmetrically on a beam (not shown) capable of rotation about its mid-point and provided with a scale and pointer indicating direction. L1 and L2 are coplanar, as are L3 and L4, and L1 and L4, and also L2 and L3 are coaxial. L1 and L3 are associated to provide one directional polar diagram and L2 and L4 the. other. Frames L1 and L3, tuned by condensers C1, are differentially connected to the grids of valves V1 and V3. L2 and L4 are similarly connected to valves V2 and V4. V1 and V3 and also V2 and V4 operate in push-pull and transformer TC is connected to both pairs as a common anode load. Valves V1-V4 are biassed almost to cut-off and the two pairs rendered effective alternately by means of a sinusoidal voltage applied to their screen grids by transformer TS, thus providing the polar diagram switching. The secondary of TC is connected to receiver REC which has a rectified pulse output J applied to multivibrator MV controlling ringing circuit I which produces the synchronized sine wave in transformer TS. The rectified pulses are also used to synchronize the horizontal saw-tooth time base TB of cathode-ray oscilloscope CRO. Output K of the receiver, of intermediate frequency, is applied to a rectifying network by switching circuits TA1 and TA2 synchronized by the sine wave applied through TS. These circuits, shown in detail in Figs. 3a and 3b (not shown), serve to reverse the output of the rectifier network so that pulses received on one polar diagram appear as deflectors above the datum line TB and pulses received on the other are indicated below it. In operation the aerial system is rotated until the two deflections E1 and E4 produced by the direct ray are equal in length. Deflections E2, E3, E5, E6, caused by indirect rays, are separated because of their longer transit time and can be ignored. In a further embodiment, Fig. 6, only two frame aerials L5 and L6, one mounted on each end of the beam, are used, and the overlapping diagrams are obtained by alternately switching resistors R5 and R6 across their respective frames by means of segments K5 and K6 on a commutator driven by motor MO. This motor is synchronized from the rectified pulse output J of the receiver REC fed by push-pull valves V12, V34. The I.F. output K of the receiver is rectified and applied through reversing segments on the commutator to the oscilloscope CRO to produce the same type of indications as in the system of Fig. 3. The time base TB of CRO is synchronized from the commutator. Mechanical switching in conjunction with a four frame aerial system is described with reference to Fig. 4 (not shown) and electrical switching with a two frame system with reference to Fig. 5 (not shown). In the system of Fig. 3, sense may be determined by switching a resistor (not shown) across the output terminals of one frame when equisignal conditions have been established. In the two frame system (Fig. 6), sense can be determined by observing the deflection pattern on rotation of the beam from equisignal position. It is stated that a hand-operated generator, switched into circuit by switch SW, can be used. if desired, to generate the synchronizing signals. Specifications 582,419 and 582,494 are referred to.