Patent GB-1039823-A (GB)
Title: Circuit for supplying a common consumer from two high-frequency current sources
IPC: H03H7/48
Filed: 1964-03-16
Abstract: 1,039,823. High-frequency bridge circuits TELEFUNKEN PATENTVERWERTUNGSGESELLSCHAFT. March 16, 1964 [March 14, 1963; April 11, 1963], No. 10954/64. Heading H1W. [Also in Division H4] A circuit for connecting two sources to a common load comprises a modified Wheatstone bridge in which the load resistances and, possibly, the balancing resistances, are replaced by the input impedances of coaxial lines which are connected at their output ends to the actual loads, the outer conductors of the lines providing inductances connected between the terminals of the bridge and a neutral point. In Fig. 1, which shows a Wheatstone bridge having load resistances RA1, RA2 and balancing resistances LAW1, LAW2, these inductances L1, L2, L3, L4 are shown connected between the terminals of the bridge I, II, III, IV and an earthed terminal O. They are, in effect, in parallel with the arms of the bridge as far as the generators G1, G2 are concerned, but their effect may be compensated by combining them with capacitors to form a #-section filter giving impedance matching over a desired band of frequencies. As shown in Fig. 2, the inductances (which may, in part, arise from mutual inductance) are provided by the outer conductors of coaxial lines K1, K2, K3, K4 whose inputs replace the arm resistances RA1, RA2, LAW1, LAW2 and which are loaded at their output ends by the resistances WR1, WR2, comprising the actual load, and resistances WL1, WL2 comprising the balancing impedances. The resistances WR each have a value equal to the original arm resistance and carry currents in phase opposition relative to earth. They therefore represent a balanced load. The terminals of the bridge are connected to the generators through condensers C1, C2 and further inductors Lq which together provide impedance matching over a wide range. The additional inductors are provided by the outer conductors of coaxial lines K5, K6, K8, K9 and the Figure shows the mode of connection of two unbalanced generators to these lines. Where the generators are balanced, it is merely necessary to connect them between the inner ends of the inductors. The generators operate in push-pull as indicated by the arrows denoting current directions. Where it is desired to feed an unbalanced load, e.g. the input of an unbalanced line, the load resistances WR1, WR2 are replaced by the circuit of Fig. 3 in which L7=L8 and L7 is realized by means of a length of coaxial line K7. The unbalanced load WR is connected to output end of the line K7. In a modification (Fig. 5, not shown), the balancing resistances LAW1, LAW2 are left in their original positions and all four sections of coaxial line are used for shifting the load resistances from the bridge arms. In this circuit, the inputs of the lines K2, K3 are in series between the terminals II, III and represent the original load resistance RA1 which can be regarded as consisting of parallel parts each of value 2R. The actual resistors WR12, WR13 replacing RA1 and WR21, WR24 replacing RA2, are, therefore, of value 2R and the characteristic impedances of the cables are also of this value. Pairs of resistances carrying inphase currents may be combined. In a modification of this circuit (Fig. 6, not shown), the inputs of the pairs of coaxial lines are in parallel and each pair of parallel inputs represents an original load resistance which may be regarded as comprising two series elements of value R/2. The coaxial lines have, therefore, a characteristic impedance of this value. In the modification of Fig. 7 (not shown), RA1 and RA2 are constituted by the inputs of coiled coaxial line connected across points II, III and IV, I. The other ends of the inner conductors are connected to earth through parallel resistors WR1, WR2 (which may be replaced by a single resistor) and the other ends of the outers are directly connected to earth. Resistors WR1, WR2 carry currents in phase and an asymmetrical output line may be connected across them. In this modification, balancing resistors LAW1, LAW2 are in the arms of the bridge between points II, IV and III, I, respectively. In the modification of Fig. 8 (not shown), LAW1 and LAW2 are removed to the centre by means of two additional coaxial lines and replaced by a single resistor WL using the same technique as in the modification of Fig. 7. In Fig. 8, the load resistance WR is shown connected across the remote end of a coaxial-line feeder whose input end is connected across K2 and K4 in parallel.