GB524457A - Improvements in or relating to antennae for short wave radio transmitters and receives - Google Patents

Abstract

524,457. Aeriais ; directive wireless signalling. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Jan. 30, 1939, Nos. 3138, 3139, 3140 and 3141. Convention dates. Jan. 29, 1938, Feb. 5, 1938, Feb. 15, 1938 and Feb. 17, 1938. [Class 40 (v)] A dipole aerial suitable for television signals comprises two conical arms, each of a length between.0.23 and 0.5 of the middle wave of the signal band, and diverging from a central feedline. The impedance of the system is normally constant over the range of side-bands, though it can be varied to meet different working conditions, such as a change in effective height, by adjusting the angle of the cone or by making part of the aerial surface cylindrical. As shown in Fig. 3, the two conical arms 1<SP>1</SP>, 2<SP>1</SP> are adjustably mounted on screw rods 5 to which the ends of the transmission line TL are connected. In Fig. 4 auxiliary rings 4<SP>1</SP> are inserted between the apex and base of the cone so as to make the end section cylindrical in shape, for impedance matching purposes. Figs. 6 and 7 show alternative forms of construction. The two aerial arms may be inclined at 90 degrees to each other, or two crossed pairs of dipoles may be used. Fig. 9 shows three conical elements 24, 25, 26 inclined mutually at 120 degrees and arranged in the same horizontal plane. They are energized by three branch lines 27, 28, 29 from the common feed-line TL. The lengths of the branch lines increase successively by one-third of a wavelength, in order to maintain the required phase-relation in each aerial element. The system is arranged half a wavelength above ground in order to cancel out vertical radiation. Fig. 11 shows a stacked array of three pairs A, B, C of crossed horizontal dipoles, placed half a wavelength apart in the vertical plane and energized in-phase by branched feed-lines 33<SP>1</SP>, 341. The aerials are supported, without the use of insulators, first at their apices by the inner conductor of the co-axial feed-lines TL, Fig. 13, and also at a point of minimum field-intensity (about one-third away from the base of the cone) by supports 46. The latter are connected to an axial rod 45 which extends between the apex of the cone and a metallic spider 44. The axial rod may also be extended through the base of the cone to meet external supporting-rods similar to 46. In this case the length of the support is made equal to an odd multiple of a quarter-wavelength, from the ground to the spider 44, in order to present a high impedance to leakage currents. Specification 469,366 is referred to.