Patent GB-718648-A (GB)
Title: Improvements in and relating to radio transmitting apparatus
Inventor: HUNT GEORGE ARTHUR
IPC: H03H7/48
Filed: 1952-06-19
Abstract: 718,648. Aerial coupling arrangements. BRITISH BROADCASTING CORPORATION. June 19, 1953 [June 19, 1952], No. 15481/52. Class 40 (5). (Also in Group XXXV] For coupling two transmitters to a common aerial, a balanced transformer is provided arranged so that there is no coup'ing between the transmitters, and switching means to modify the transformer connections enable energy to be fed to the aerial from one of the transmitters only without substantial loss in the coupling. In one embodiment, the switching arrangements enable any one, any two or all of three transmitters 11, 12, 31 to be coup'ed to a common aerial feeder 38. The relay contacts are all shown in their unoperated positions. When each transmitter is in use it provides a 30-volt D.C. output for relay operation. When all three transmitters are in operation, relays A, B, C, D and F are energized. The outputs of transmitters 11, 12 are led to tappings 14, 17 of windings 15<SP>1</SP>, 15<SP>11</SP>of the balancing transformer 15 through contacts D2, A2 and F3, B2, respectively, the common output at the junction of windings 15<SP>1</SP>, 15<SP>11</SP>being fed to contact C2. A balancing resistance 24 is connected between tappings 14, 17 by contacts A3, B3 and the free ends of the windings are disconnected from earth by contacts A1, B1. A condenser 23 may be connected across the coils to adjust the impedance. The combined output of transmitters 11, 12 is thus connected through contact C2 to the combining network 37 to which is also fed the output of transmitter 31 through contacts F4, D3. The network comprises two feed condensers 39, 40 and two inductances 41, 42 connected in series therebetween and in parallel with a balancing resistance 43. The junction of inductances 41, 42 is connected to earth through a condenser 44 and inductance 45, the junction therebetween being connected through contact Cl to the aerial feeder 38. If transmitter 31 is switched off, relay C becomes de-energized and the output from transformer 15 is fed directly to feeder 38 through contacts C1, C2. If only transmitter 12 is switched off, relay F becomes de-energized, relay B is energized from transmitter 31 through contact Fl, and relay C is deenergized by the opening of contact F2. The output of transmitter 31 is thus diverted to transformer 15 through contacts F4, F3 and the feeder 38 is connected directly to this transformer through contacts C1, C2. If only transmitter 11 is switched off, relay D becomes de-energized and, in a similar way, the output of transmitter 31 is transferred to transformer 15 through contacts D3, D2. If transmitters 11, 12 are both switched off, only relay B remains energized, the transmitters are disconnected by contacts D2, F3 from the transformer 15 and the output of transmitter 31 is fed through contacts F4, F3. B2 to the tapping 17 on winding 15. The winding now acts as an auto-transformer the lower end being earthed by contact A1. A similar circuit is set up if one of the other transmitters is functioning alone. The construction of a suitable winding 15 is described (see Group XXXV). The switching may be control'ed by an automatic monitor as described in Specification 717,083.