Patent GB-149282-A (GB)
Title: Improvements in and relating to the reception of wireless signals
IPC: H04B1/16
Filed: 1920-07-15
Abstract: 149,282. Marconi's Wireless Telegraph Co., (Assignees of Goldsmith, A. N.). July 28, 1919, [Convention date]. Wireless telegraphy and signalling.-Continuous-wave signals are broken up or @ at the receiving-station at an audible frequency by rapidly and periodically varying the mutual inductance between coupling-coils in the receiver circuits. The mutual inductance is preferably varied by intermittently placing a conducting- plate or a short-circuited coil between the coupled coils. Fig. 6 shows one arrangement, Fig. 7 is a side view of the rotary disk, Fig. 12 shows another arrangement, and Figs. 14, 20, and 21 are substitutes for the rotary disk. The aerial A is connected to earth through inductance coils C, D, T, of which D is coupled to a coil F in the secondary circuit. This circuit includes other coils G, U, and a detector J and telephone K connected across the condenser H. A toothed disk L, of good conducting material such as copper or silver, is rotated at adjustable speed by a motor and has its teeth projecting into the gap between the coils D, F. When a tooth R lies opposite the coils, the mutual inductance of the coils is reduced practically to zero, so that no current passes through the telephone. A note is thus heard in the telephone of a pitch determined by the number of teeth on the disk L and its speed of rotation. The quality of the note is dependent on the shape of the teeth. To prevent the aerial and the secondary from being de-tuned by variation of the self-inductance of the coils D, F, the coils T, U are so placed relatively to each other and to the teeth on the disk L that while they have negligible mutual inductance, their self-inductance is, by the passing of the teeth, varied in opposite phase to the variations in the coils D, F. The teeth form an electrostatic shield between the coils D, F as well as an electro-magnetic shield, and may be grounded for this purpose. The incoming waves may be amplified by suitable relays before or after they are given a tone frequency by the rotary disk. Audio-frequency amplifiers may also be employed. In the modification shown in Fig. 12, the primary coils V, X and secondary coils W, Y are oppositely wound on parallel formers and the teeth on the disk L are spaced so that one tooth is opposite the alined coils V, W when an adjacent tooth is opposite the alined coils X, Y. This arrangement of the windings causes the couplings to add their effects in the secondary circuit, whereas external magnetic fields produce no effect. The coupling-coils and disk may be enclosed in a grounded metal box, and the amplifiers and detectors may be similarly enclosed. Grounded conducting-sheaths may enclose the leads. A cylinder or cone q, Fig. 14, with wavy edge r may be substituted for the disk, one of the coils D being within and the other F outside. A cylinder of non-conducting material with a series of spaced conducting-plates forming a ring may be employed. A circular disk x of conducting material may have a ring of perforations as shown in Fig. 20. Fig. 21 shows a conducting-annulus y placed between the coils D, F and alternately open-circuited and short-circuited by a toothed rotary member z; or the annulus may be rotated about an axis parallel to its own.