Patent GB-580570-A (GB)
Title: Improvements in or relating to keying devices for high frequency circuits
IPC: H01Q3/24
Filed: 1944-04-24
Abstract: 580,570. Modulating apparatus ; directive wireless systems. STANDARD TELEPHONES & CABLES, Ltd., and WILLOUGHBY, E. O. April 24, 1944, No. 7628. Addition to 580,481. [Class 40 (v)] In a radio-frequency commutating arrangement in which a circuit is coupled to each of three or more transmission lines by reactance networks which together with additional reactance elements form potential dividers providing zero voltage at the transmission line inputs, a rotatable member is adapted to modify each reactance network in turn to permit transmission to the associated line for a definite time which is the saine for all the transmission lines. In the arrangement shown in Figs. 1, 3 and 4 for connecting one input (or output) line I to each of three output (or input) lines P, Q, R, in turn, the lines are attached to a cylindrical metal casing 1 and are closed near their upper ends by adjustable short-circuiting plugs 2, 3, 4 and 9 to form matching stubs Ig, Pg, Qg and Rg. The inner conductor of input (or output) line I is connected to a fixed horizontal disc 8 while the inner conductors of lines P, Q, R are terminated in U-shaped metal shoes 5, 6 and 7. Parallel to disc 8 is arranged a cam-shaped disc 10 rotatably mounted on a shaft 11 which passes through a bearing 14 at the lower end of a short tube 15 forming a reactance connecting disc 10 to the casing 1 which is at earth potential. The disc 10 has a cut-away portion occupying about 240 degrees, having a projecting sector 13 of sufficient radius to enter the shoes 5, 6, 7 and engage one shoe at a time. Three adjustable two-wire stub lines Ip, Iq, Ir (not all shown in Figs. 1 and 3) are provided connecting the disc 8 to each of shoes 5, 6 and 7. With the disc 10 in the position shown, waves from line I pass through the relatively large fixed capacity Id between discs 8 and 10 and thence through the relatively large capacity Dp+Da between disc 10 and shoe 5 to the line P, or vice versa, which forms a high efficiency transmission path when the stubs are correctly adjusted. Smaller capacities Dq and Dr (equal to Dp) exist between the cutaway portion of disc 10 and shoes 6 and 7 and the corresponding stubs Iq, Ir are adjusted to eliminate the effects of these small capacities so that no energy is transmitted to lines Q and R. Stub Ip is similarly adjusted so that when disc 10 is moved from the position shown, and only capacity Dp exists to shoe 5, no energy is transferred to line P. The excess capacity Da is thus transferred to each line in turn by rotation of disc 10, which is driven by a motor 12 so that efficient transmission occurs for about one-third of a revolution to each line, the other two lines being blocked. The stubs Ip, Iq, Ir are located in tubular extensions of the case 1 and therefore introduce shunt reactances in parallel with the matching reactances Ig, Pg, Qg, Rg. In order to prevent these added reactances from disturbing the matching requirements, the outer tubes and inner conductors are extended beyond the short-circuiting bridges such as 16, which are isolated from the tube, so that the total length of each stub is equivalent to half a wavelength and provides a very large shunt reactance with negligible effect. The adjustment of the stubs is not critical and in a modification, Fig. 7 (not shown), they may be replaced by small fixed inductance coils enclosed in screens. Any number of lines similar to P, Q, R may be arranged symmetrically around the casing 1, the angular widths of sector 13 of disc 10 and of the terminal shoes being so adjusted that transmission occurs to one line only at a time. If a large number of lines is employed, the diameter of disc 10 may be increased to reduce the periods during which changeover from blocking to unblocking of each line occurs. To avoid additional. reactance in series with the capacity Dp+Da, the radius of sector 13 should be less than about #/8 or lie between n# and n# + #/8, where n is an integer. When the switch is employed to supply modulated waves to three lines in turn and it is required that the modulation should be different, a commutator comprising four discs 21, 22, 23 and 24, with corresponding brushes, mounted on the shaft 11, Fig. 3, may be employed. The disc 21 is divided into three insulated segments, each of which is connected to one of the other undivided discs. The three modulating signals are supplied respectively to discs 22, 23 and 24 and the brush corresponding to disc 21 supplies the modulating signal to the transmitter. Alternatively, the transmitter may be provided with three normally blocked modulation sources and an unblocking potential fed to disc 21 may be passed,via disc 22, 23 and 24 to unblock the modulation sources in turn. Specification 580,484 is referred to.