Patent GB-744419-A (GB)
Title: Improvements in and relating to electric switching apparatus
Inventor: ELLIS HORACE DUDLEY MCDONOGH
IPC: H04N5/268
Filed: 1953-04-22
Abstract: 744,419. Automatic exchange switches: intercommunication systems. BRITISH BROADCASTING CORPORATION. July 21, 1954 [April 22, 1953], No. 11096/53. Class 40 (4). [Also in Group XL (b)] Switching apparatus for radio-frequency circuits consists of a uniselector having outlets connected to every other bank contact of two levels, between which levels there is an intermediate level, the unused contacts of the two levels and all the contacts of the intermediate level being effectively grounded so as to reduce cross-talk between the circuits. The invention is described with reference to a switching arrangement (Fig. 4) for connecting any one of a number of television programme sources to any one of a number of destinations, providing two video-frequency circuits, four 2- wire audio-frequency circuits and four single wire D.C. signalling circuits per source. Only four uniselectors 36, 37, 39, 40 are shown and only two levels of each. The levels 361, 371, 39<1> and 40<1> which serve for the switching of the video circuits have every other contact grounded, and are assumed to be adjacent to levels having all contacts grounded. The connections between levels 36<1>, 37<1>, 39<1> and 40<1>, although shown as single conductors, are coaxial cables. The incoming audio-frequency lines 46, 48 are connected to the wipers of levels 36<11>, 37<11>, the bank contacts of which are multipled, and connected to the outgoing audiofrequency lines; whereas the incoming D.C. lines 47, 49 are multipled to the banks of levels 39<11>, 40<11>, the wipers of which are connected to the outgoing D.C. lines. A control panel for controlling the switching arrangement (Fig. 5) comprises a jack, e.g. 56, for each destination, which normally contains a plug carrying an illuminated window bearing the number of the destination. Corresponding jacks, e.g. 57, are provided for each source; and lamps, e.g. 58, 59, are provided above each jack. In Fig. 6 one destination jack is shown at 56 and one source jack at 57. Relay circuits associated with the uniselector D for destination 3 are enclosed by the broken line 60, and those associated with uniselector S for source C by the broken line 61. With the plug 62 inserted in jack 56 the lamp (not shown) in the plug is lit over the tip and ring of the jack. To connect a source to a destination, the plug is removed from the destination jack and inserted in the source jack. Removal of the plug 62 brings up relay KA which lights the destination lamp 59 and prevents operation of other relays KA. On insertion of the plug 62 in the source jack 57, the lamp in the plug is lit and relay KB is operated, thus marking the contact in bank DL1 appropriate to source C and energizing motor unit DM. Uniselector D thus drives to the marked contact whereupon high speed relay TA pulls up to cut the drive, and bring up WA. The consequent operation of WB applies a marking to the destination 3 contact of SL1, and other contacts (not shown) of WA and WB complete the wiper circuits of the audio frequency and D.C. signalling levels of uniselector D. The off-normal contacts DM2 complete a driving circuit for SM which is interrupted by the operation of TB when the marked contact is reached. WD and WE pull up in turn, whereupon KB and KA are released and lamp 58 is lit to indicate that the desired connection has been established. Lamp 59 is extinguished on the release of KA to show that a further selection may be made. Removal of the plug 62 from the source jack 57 releases WD and WA, whereupon WE and WB fall away and the uniselectors S and D are homed.