| 摘要 |
1,236,364. Aerials. OFFICE DE RADIODIFFUSION - TELEVISION FRANCAISE. 28 April, 1969 [30 April, 1968], No. 21601/69. Heading H4A. An aerial for use within the M.F. band (300 to 3000 kHz) comprises a vertical, grounded metal pylon 1, Fig. 3, which has a height of substantially a wavelength at the nominal frequency of operation and which, as described, is of lattice type and of triangular cross-section. Extending around the pylon is a skirt of conductive wires 2 which are suspended from outriggers 3, and which are kept taut by guided counterweights 5, one being provided for each pair near ground level. A rod insulator 9 is provided in each wire 2 at its mid-point, and another rod insulator 10 is provided above the counterweight 5. The wires are connected together every 15 metres by horizontal conductive wires girdling the skirt. Besides being connected to the pylon at its top, each wire is further connected to it at points which are, respectively, one-, two- and three-fourths of the pylons length from its top. At each said point an articulated linkage comprising a triangle 12, Fig. 7, is provided between a U-link 13 engaged on the wire 2, and beams 11 on the pylon 1. The linkages are bridged by conductive jumper wires to ensure electrical continuity. The aerial is supplied by a coaxial feeder 14, which runs up the inside of the pylon 1. The feeder comprises a central conductor (15), Fig. 4 (not shown), which is supported by insulators inside an outer sheath of conductors (16). As is shown in Fig. 3, the central conductor of the feeder 14 is connected to the skirt of wires 2 at a point in the upper half thereof, adjacent its centre, said point being selected to match the aerial and feeder impedances. The feeder is continued up the pylon, and a short-circuit CC1 acts as a means of adjusting reactance at the feed point. A short-circuit CC2 between the bottom-half skirt of wires 2 and the pylon provides compensation for the capacitance to earth of the end of the bottom half-skirt. |
