GB493860A - Improvements in or relating to aerial feed and aerial tuning circuit arrangements - Google Patents

Abstract

493,860. Impedance networks; wireless receiving and multiplex systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., RUST, N. M., and RAMSAY, J. F. April 15, 1937, No. 10773. [Classes 40 (iii) and 40 (v)] An impedancematching network for connecting an aerial AE or a receiver to a feeder 2 is tapered or composed of asymmetrical sections whose image impedances at a required frequency form a progression while their image transfer constants are equal throughout. Two aerials for alternative use may be permanently so connected to the same feeder. Impedance-matching networks. A balanced aerial AE, Fig. 1, may be coupled to the unbalanced feeder 2 through a network 41 which is balanced at the aerial end and unbalanced at the feeder end, while the inductances and condensers change in magnitude progressively, as shown, so that the impedance is matched at each end. Instead of the lowpass network shown in Fig. 1, a high-pass network may connect a frame aerial to the feeder, Fig. 2 (not shown), or a band-pass network may be used, Fig. 4 (not shown); and the sections may be of the L instead of the H type, Fig. 3 and Fig. 4 (not shown), or of lattice, bridged-T or other type. The Specification gives the theory of tapered matching. The ratio B of input image impedance to output image impedance is the same for each section, but the output impedance for one section is equal to the input impedance for the next section. The image transfer constant is the same for all sections. Then B varies with frequency, but the matching is exact for a selected frequency, such as the geometric mean frequency of the working range, and errors in matching at neighbouring frequencies are reduced by increasing the number of sections. The cut-off frequency of the network is arranged to be outside the working range. Tuning feeders for reception. The tuner T, Fig. 5, may be inserted in the middle of the feeder, Fig. 5, which is then matched to the aerial and receiver by networks 41, 41<1> respectively ; the tuner may be a simple resonant circuit in series with the core of the feeder, Fig. 6 (not shown), or a tee-section with series inductances and shunt tuning condenser, Fig. 7 (not shown), or it may comprise a pair of coupled inductances, Fig. 8, in series with unitarily controlled and symmetrically earthed condensers. A long-wave-stopper condenser of 1,000 ÁÁF. may be interposed. Multiplex wireless telegraphy. A medium- and-long-wave aerial AE is connected to a feeder 2 through a low-pass network 41 with tapered image impedance, and a short-wave aerial 7 is connected to the same feeder through a similar but high-pass network 42. The aerials are for alternative use, but both are permanently connected to the feeder. The networks 41, 42 are tapered, the inductances and condensers changing progressively in magnitude from one end to the other, as shown, for the purpose of matching the impedances.