Patent GB-358634-A (GB)
Title: Improved switch for audio or radio frequency electric circuits
IPC: H01P1/12
Filed: 1930-07-31
Abstract: 358,634. Two-way terminal equipment. STANDARD TELEPHONES & CABLES, Ltd., DUNHAM, C. R. and CRADDOCK, D. A., Columbia House, Aldwych, London. July 31, 1930, No. 23107. [Class 40 (iv).] Switches for A.C. audio or radio frequency circuits, more especially the change-over switches for submarine cable telephony in which one branch of the change-over circuit, for example the transmitting branch, is at a relatively high energy level as compared with the other branch such as the receiving branch, are provided with co-operating contact members separated by an electrostatic screen having an aperture through which the contacts operate, the aperture being automatically closed when the co-operating contacts are separated, thus preventing leakage between one branch and the other of the controlled circuits. As applied to the system shown in Fig. 1, S is the double-pole change-over switch and switch blades 1, 4 adapted to connect the submarine line LW by contacts 2, 5 to a transmitting path A2 or by contacts 3, 6 to a receiving path Al both paths being connected in turn through a hybrid coil H to a land line LE. Each set of the contacts of the change-over switch is arranged as shown in Fig. 3, a double-ended contact 13 carried by a pivoted arm 14 being adapted to be connected to a contact 8 on an arm 7 or a contact 17 on an arm 18. Between the relatively fixed and movable contacts, however, are intermediate contacts 11, 15 carried by pivoted arms 10, 16 and normally closing apertures formed in earthed screening members 9, 19 separating the co-operating contacts. Thus when the centre contact is moved, either manually or electromagnetically to close one or other of the branch circuits it first engages the intermediate member 11 or 15 and is momentarily earthed and afterwards moves through an orifice in the screening member to move the intermediate member away from the screen and into contact with the contact 8 or 17 so closing the corresponding branch circuit. The disposition of the screening members 9, 19 prevents capacity coupling and leakage between the two branch circuits and the central movable contact may also be completely screened by a copper tube 20. In a single-way switch, Fig. 1 (not shown), the latter may be omitted. In a modification shown in Fig. 5 the co-operating contacts 24, 25 are disposed in apertures 23, 30 formed in relatively movable metal screening drums 21, 22. When the co-operating contacts are separated by clockwise rotation of the inner drum the apertures in the drums are no longer in register but if the rotation in a clockwise direction is continued the movable contact 24 is moved into engagement with a second fixed contact 29 corresponding to the second controlled circuit the contact 29 being disposed within a corresponding aperture of the outer drum. The fixed contacts 24, 29 of the two circuits are screened additionally from each other by a vertical earthed screening member 26. The fixed contacts are carried by spring arms 31 secured to terminals 32, the movable contacts, which with the fixed contacts are duplicated in the case of a double pole switch, being secured to the insulating drum within the rotatable screening drum 21.