US2013140A

US2013140A - Translating circuit

Info

Publication number: US2013140A
Application number: US633423A
Authority: US
Inventors: Harald T Friis
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1932-09-16
Filing date: 1932-09-16
Publication date: 1935-09-03
Anticipated expiration: 1952-09-03

Description

Sept. 3, 19350, H, T, FRHS 2,013,140

TRANSLATING CIRCUIT Filed Sept. 16, 1952 L 2 ""Yf UNBALANCEDQ BALANCED CIRCUIT BALANCED CIRCUIT CH I }UNBALANCED CIRCUIT //v VENTOR h. 7? FRI/5 AT TORNEV Patented Sept. 3, 1935 PATENT OFFICE TRAN SLATING CIRCUIT Harald T. Friis, Rumson, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application Septemberql6, 1932, Serial No. 633,423

11 Claims.

This invention relates to electrical wave transmission systems and more particularly to coupling devices for high frequency signaling systems.

In the design of high frequency signaling systems there is frequently met the problem of coupling a balanced circuit to an unbalanced one. The difficulty usually involved is prevent the unbalanced circuit, one side of which may be .at ground potential, from disturbing the electrical balance with respect to ground of the other circuit. The maintenance of the balanced condition at high frequencies such as employed for short wave radio communication is complicated by the fact that the introduction of the slightest difference in the capacitance of the sides of the balanced circuit to ground may materially affect the efficient operation of the system. So critical are such circuits in this respect that special attention must be given to the small capacitances existing between the windings of transformers and other circuit elements.

An object of the present invention is to provide means for coupling an unbalanced circuit to a balanced circuit without disturbing the electrical balance of the latter.

Other objects and features of the invention will appear in the following detailed description of a specific embodiment of the invention. The accompanying drawing shows in Fig. l a coupling device heretofore proposed; in Fig. 2 a coupling device in accordance with the present invention; and in Fig. 3 an application of the coupling device of Fig. 2.

Coupling devices of the type shown in Fig. 1, it has been noted, have been suggested heretofore. The balanced circuit l is connected to the terminals of a continuous winding L2, L3 which at its midpoint is grounded. The unbalanced circuit 2 is connected to the parallel-connected windings L1, L4, which are disposed in inductive relation with the balanced winding and on respectively opposite sides thereof with their grounded terminals adjacent the line terminals of the latter winding. With this method of connection, it will be observed that the respective sides of the balanced circuit are capacitively connected to ground through the inherent interwinding capacitances. The capacitance C1-2 existing between windings L1 and L2 is effectively between the upper side of the balanced line I and ground, and the capacitance C34 existing between windings L3 and L4 is, in effect, similarly connected between the other side of the balanced line, I and ground. The balance of circuit l is therefore made dependent on an exact equality between these two inherent capacitances.

Referring now to Fig. 2 there is shown a specific embodiment of the present invention comprising a balanced transformer, the windings of which are so disposed relatively to each other and so connected as to minimize the possible unbalancing effect of inter-winding capacitances. The balanced circuit I is in this case connected to the adjacent terminals of the windings L2 and L3, the outer terminals of these windings being connected together, preferably by virtue of their respective direct connections to container 3. Windings L2 and L3 are so arranged as to be inductively in series-aiding relation. Windings L1 and L4 .are arranged on respectively opposite sides of the central windings. Their adjacent terminals are connected together and to the grounded side of the unbalanced circuit l, preferably by respective direct connections to container 3. Their outermost terminals are similarly joined to the high potential side of the unbalanced circuit. The winding directions of L1 and L4 are opposite to each other so that the voltages induced in these windings are in phase agreement with respect to the unbalanced circuit. The container 3, which may be of copper or other suitable material is used to shield the transformer against external interference.

The physical dimensions of the windings and the separation between windings may, of course, be varied within wide limits. In one air-cored transformer which was found to operate satis factorily at a wave length of I approximately twenty meters, windings L2 and L3 were solenoidal is form and comprised two turns each of one-eighth inch copper tubing wound on a three inch form. Windings L1 and L4 comprised four turns of the same diameter separated approximately an inch from the central windings. The dimensions of shield 3 may be determined by the maximum allowable values of the capacitances C1O and C4 o existing between the shield and the outer turns of windings L1 and L4, respectively. Provision may be made also for moving the central windings axially so that an exact electrical balance can be more readily obtained.

Direct capacitive conn tion to ground from the terminals of the balanced circuit l, as Fig. 2 shows, is substantially eliminated. The possibility of capacitive unbalance of that circuit is therefore minimized. Of the inter-Winding capacitances that are present, none tend toward unbalance. The capacitance C24 between L2 and L3 shunts the balanced circuit but does not affect the electrical symmetry with respect to ground. Capacitances C14 and C34 are terminated at points of ground potential, i. e., the adjacent terminals of windings L1 and L4, respectively. They have no effect on the balanced circuit, however, since their points of connection with the latter circuit are the outer turns of windings L2 and L3, which, being at the mid-potential of the balanced circuit, are likewise at ground potential.

The shunt capacitance C2 3 referred to is disadvantageous in some systems. Its magnitude may be reduced by increasing the separation of windings L2 and L3, or by arranging the windings in accordance with the invention of A. G. Jensen, disclosed in his application for Letters Batent b'earing "Serial No. 632,097 and filed September: 8, 1932.

In other systems, as in that shown in Fig. 3, this capacitance may cooperate with additional shunt capacitive elements to tune the system. In Fig. 3 is shown an application of the transformer of Fig. 2 to a directional radio receiving system employing a balanced antenna systemA, which may be, for example, of the horizontal double V or rhomboid type. The directional characteristic of the antenna, which depends to alarge degree on the balance of the coupling circuit, is preserved by the use of a transformer T in accordance with the present invention. A condenser C1 connected across the antenna A and the balanced side of transformer T is used for tuning'purposes. The unbalanced side of the transformer T is connected through a tuning condenserCz to a transmission line CL comprising' coaxial conductors '4 and 5, which leads to the remotely located radio receiver R.

"Although the present invention has been described with reference to a specific embodiment of it, it is not thus limited in nature but is capable of various other embodiments within the spiritand scope of the appended claims.

What is claimed is:

1. In a high frequency transmission system, a balanced circuit and an unbalanced circuit and an air-cored transformer coupling said circuits, said transformer comprising a first pair of windings axially spaced and connected to said unbalanced circuit in parallel-aiding relation, a second pair of windings arranged between and in symmetrical relation to said first pair of windings; the ad'jaceiit terminals of said second pair of win'dingsbeing connected to said balanced circuit the other terminals of said second pair of windings being connected together.

"'2. Ina high frequency transmission system, a balanced circuit, an unbalanced circuit, and a transformer coupling said circuits, said transformer comprising a first pair of windings axially spaced and connected in parallel to said unbalanced circuit, adjacent terminals of said windin gs being connected together and to ground, a second pair of windings positioned symmetrically between and in balanced inductive relation to said first pair of windings, said second pair of wind ings being arranged in series-aiding relation with adjacent terminals thereof connected to said balan'c'ed circuit.

3. A high frequency air-cored transformer comprising four solenoidal windings disposed at spaced intervals along a common axis, a pair of terminals connected to the adjacent ends of the two central windings, a connection between the other ends of the central windings, means connecting the inner ends of the outer of said four windings, means connecting the outer ends of said outer windings, and a pair of terminals con nected to said connecting means.

4. In a high frequency transmission system, a balanced circuit and an unbalanced circuit, and an air-cored transformer coupling said circuit, said transformer comprising a pair of windings connected to said balanced circuit, a pair of windings connected. to said unbalanced circuit, said pairs of windings being in inductive relation and symmetrically positioned with respect to each other, the ends of said first-mentioned windings adjacent said second-mentioned windings being at substantially the midpotential of said balanced line.

5. In a high frequency transmission system, a balanced circuit and another circuit and an aircored transformer coupling said circuits, said transformer comprising two pairs of inductively related windings, connections from said balanced circuit to corresponding ends of a symmetrically positioned pair. of said windings, said symmetrically positioned pair of windings presenting to tlieothers of said windings only their low potential ends, and said other circuit being connected to said other pair of windings.

6. In a high frequency transmission system, a balanced circuit and another circuit, and an aircored transformer coupling said circuits, said transformer comprising a multiplicity of windings, two of said windings being connected in series with each other and with said balanced cir-.- cuit, said two windings being so positioned that the high potential ends of said two windings are substantially free from inter-winding capacitances to ground, and connections from a plurality of the other of said windings to said unbalanced circuit.

'7. In an electrical signaling system, a balanced circuit and another circuit, and a transformer coupling said circuits, said transformer comprising a plurality of windings connected to said other circuit and aplurality of windings inductively balanced and symmetrically positioned with respect to said first plurality of windings and'connected to said balanced circuit, the terminals of said second plurality of windings that are connected to said balanced circuit being not adjacent windings comprising said first plurality of windings.

8. A balanced circuit, another circuit, a high frequency transformer comprising four nonoverlapping windings symmetrically disposed along a common axis, means for connecting a pair of said windings in parallel to said other circuit, means for connecting the other pair of said Windingsin series to said balanced circuit, only the low potential ends of said other pair of wind ings being adjacent said first pair.

9. A combination in accordance with claim 8 in which the low potential ends of said first pair of windings are adjacent the low potential ends of said other pair of windings.

10. In a system for coupling a single ended circuit with a double ended circuit, comprising a transformer having a pair of primary windings and a pair of secondary windings, one pair of said windings being woundin opposite directions and connected in parallel in said single ended circuit and the other pair of windings being wound in the same direction and connected in balanced relation in said double ended circuit, and the points of zero alternating potential on both pairs of windings being placed in close proximity to each other;

11. In a system for coupling a single ended circuit with a double ended circuit, comprising a transformer having a pair of primary windings and a pair of secondary windings, one pair of said windings being wound in opposite directions and connected in parallel in said single ended circult and the other pair of windings being wound in the same direction and connected in balanced relation in said double ended circuit, said pairs of windings being so spaced relative to each other HARALD T. FRIIS.