June 27, 1967 B. , MILES 3,328,527 SINGLE CONDUCTOR AUDIO FREQUENCY SIGNAL AND D. C. SWITCHING TRANSMISSION SYSTEM Filed July 24, 1964

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s INVENTOR. BARRY L. MILES "/4 a.A6 e ATTORNEYS 3,328,527 United States Patent Office Patented June 27, 1967 2 The single conductor audio frequency signal and D.C. 3,328,527 Switching transmission system 10 is shown to have an SINGLE CONDUCTOR AUDIO FREQUENCY SIG audio input/output circuit 11a capable of impressing an NAL AND D.C. SWITCHING TRANSMISSION SYSTEM audio signal across coil 12a with, for example, a 3 volts (Sarry . Miles, Cedar Rapids, Iowa, assignor to Collins peak value. Coil 12a, wound as an input coil on tape Radio Compa Bay, Cedar Rapids, Iowa, a corporation Wound toroid core 13a, can also act as an out of Iowa put coil for an audio signal flowing the other way in feed Filed July 24, 1964, Ser. No. 384,886 ing such an audio signal as an output to audio input/out 8 Claims. (C. 179-3) put circuit 11a. 0 When coil 12a is used as a signal input primary coil This invention relates in general to signal combining, of transformer 14a, coil 15a is the audio signal second conveying, and then signal separating systems, and in ary coil and has a current return to ground from one particular to system circuitry for combining and then end through capacitor 16a. Coil 15a also has a connec Separating a D.C. signal and an audio frequency tion from the other end through single conductor trans signal for most economically utilizing a limited number 5 mission line 17 to an end of coil 15b of transformer 14b. of cable connections between various component loca The other end of coil 15b has a current return to ground tions in the system. through capacitor 16b. For convenience and ease of un In various electronic equipment installations, for ex derstanding, components on the left side of the drawing, ample in many vehicles, particularly military vehicles, having a similar or duplicate component on the right side, including tanks, aircraft, and nautical vessels having mul 20 are given an 'a' identification, and on the right side tiple electronic component stations, the trend to greater a "b' identification. use of electronics and toward more and more sophisti Coil 15b acts as an input primary coil for transformer cated electronic systems has tended to lead to excessive 14b with passage of audio signals from the 'a' side to numerical requirements in cabling circuits. the "b' side of transmission system 10 and on the other It is, therefore, a principal object of this invention 25 hand as an output secondary coil with passage of audio to combine and then separate D.C. switching current and signals from the "b' side to the 'a' side of transmission an audio frequency signal for most economically utilizing system 10. Coil 15b is wound on toroid transformer core a limited number of cable conductors between two elec 13.b in the same manner as with coil 15a on transformer tronic component stations in a system. core 13a; and secondary or primary coil 12b, dependent Another object is to provide substantially mutual isola 30 upon the direction of audio signal flow, is wound on tion between D.C. and audio signal currents in their re transformer core 13b in the same manner as coil 12a is Spective separate input and output circuits to and from wound on transformer core i3a. Coil .2b is connected a common single transmission line. for feeding therein induced audio signals to audio out A further object is to provide immunity to audio sus put/input circuit 11b for utilization as desired. When ceptibility interference orginating from any ripple cur 35 audio output/input circuit 11b is acting in reverse, it rents that may occur in the D.C. switching current. supplies an audio signal impressed on coil 12b as a pri Features of this invention useful in accomplishing the mary input coil for reverse passage of audio signals. above objects include a single conductor transmission line It is an important design factor that capacitors 16a and interconnecting two electronic component stations for 16b have negligible capacitive reactance compared to conveying audio frequency signals in both directions be 40 the inductive reactance of the respective choke coils 21a tween the stations and, simultaneously, D.C. signal cur and 21b, in order to avoid resonance effects through the rents between the stations. The transmission line is con audio frequency range. This requires that the capacitors nected between a transformer coil winding of an audio 16a and 16b be relatively large; for example, in a work signal transmitting transformer in one of the stations ing embodiment as illustrated, capacitors 16a and 16b and a corresponding coil winding in the other station. 45 were 100 microfarad capacitors. Furthermore, coils 12a Each of the electronic component stations also includes and 12b, and 15a and 15b must have sufficient coil a D.C. signal and/or control voltage circuit connected to turns to adequately support inductive transmission of sine the single transmission line. These connections to the wave audio signal even at the lowest output transmission line each include a coil bifilar wound with audio frequency. Such a number of turns requirement the respective audio transmitting-receiving transformer 50 may be derived from the following formula: coil so that the same current flow passes through each of the coils bifilar wound in a transformer of each of the E=4.44B max A.Nfx10-8 stations, and the bifilar wound coils are so polarized that where: the D.C. current flow of one coil of each bifilar winding is E=R.M.S. signal voltage opposite to D.C. current flow in the other companion coil 55 B max=peak flux density in gausses of the same bifilar winding. Each of the two coil bifilar A =magnetic path cross section in square centimeters windings is provided, in the respective stations, with an N=number of turns audio frequency current return to ground through a ca f=frequency in cycles per second pacitor. A choke coil is also provided between each 4.44=coefficient for sine wave R.M.S. input D.C. signal and/or control voltage circuit and the re 60 10 =conversion factor from cgs. to mks. units. Spective station bifilar coil windings as part of the con A D.C. signal and/or control voltage circuit 18 is nection therebetween. The capacitors are so chosen as to provided for feeding a D.C. signal and/or control voltage have negligible capacitive reactance compared to the in input through transformer coil 19a to the common junc ductive reactance of the respective choke coils in order to tion of coil 15a and capacitor 16a, and through coil 15a avoid resonant effects through the audio frequency range. 65 to and through single conductor transmission line 17 for Obviously, audio signal transmitting-receiving transform transmission of a signal from the left “a” side to the er coils, provided with the , are connected right "b" side of the system. On the “b' side of the system to audio input/output circuits in each of the stations. Such D.C. signal and/or control voltages are passed A specific embodiment representing what is presently through coil 15b to the common junction of coil 15b and regarded as the best mode of carrying out the invention 70 capacitor 16b, and from this common junction through is illustrated in the accompanying drawing. coil 19b to D.C. signal and/or control voltage utilizing Referring to the drawing: circuitry 20. In combining such D.C. signal and/or con 3,328,527 3 4. trol voltage (for example as a switching current) and less than the base-to-emitter voltage of 31, in the an audio signal being passed through the single transmis saturated state, with transistor 31 thereby being in the sion line 17 of the system, any D.C. current passed must biased-off state. Manual closing of switch 23 effectively pass through each of the transformer coils 15a and 15b. places the base-to-emitter voltage of NPN transistor 24 Since tape wound toroid cores are very susceptible to 5 at zero volts thereby turning off transistor collector cur D.C. saturation and various other transformer magnetic rent. This results in the collector-to-emitter voltage of circuits are susceptible to various levels of D.C. Satura transistor 24 tending to rise toward the voltage of positive tion, coils 15a and 19a are together bifilar wound on voltage supply 25. However, this rising action is limited toroid transformer core 13a of transformer 14a with coil since the base-to-emitter junction of NPN transistor 31 winding polarizations as dot indicated on the drawing. O acts as a forwardly biased resting at an NPN tran Coils. 15b and 19b of transformer 14b are bifilar wound sistor 24 collector-to-emitter voltage value equal to an in like manner on toroid transformer core 13b. With this NPN transistor 31 base-to-emitter voltage in the saturated bifilar coil winding in each of the transformers, the cur state with transistor 31 being thereupon turned on. This rent is the same through each bifilar wound coil and flow results in relay coil 32, in series with the collector-emitter ing in the opposite direction in one coil from the direction circuit to voltage supply 34, being activated and relay of current flow in the other coil. This provides a net elec 33 being energized. tromagnetic cancellation effect and transformer inductive Components and values used in a working single con ly transmitted audio signals are not adversely affected by ductor audio frequency signal and D.C. switching trans D.C. originated toroid transformer core saturation. mission system according to the invention as shown in the Obviously, other transformers having various other 20 drawing, include the following: magnetic circuit configurations may be utilized in place Coils 12a and 12b ------, 200 turns No. 32 wire. of the toroid core transformers shown, with, however, Coils 15a, 15b, 19a, and 19b - 20 turns No. 32 wire. the employment of bifilar type windings having appro Capacitors 16a and 16b ----- 100 microfarads. priate coil polarization to minimize any D.C. derived Choke coils 21a and 21b ---- 200 turns No. 32 wire on magnetic circuit saturation to such negligible levels as to 25 ferro-magnetic cores. permit substantially unimpeded transformer transmission NPN 24 and 31- 2N2270. of audio signals. Voltage supplies 25 and 34--- --22 to 28 volts D.C. It should be particularly noted that audio reactor coil 26------3.3K ohms. windings 21a and 21b, shown, for example, to be wound 27 and 28------1.5K ohms. on powdered iron ferromagnetic cores 22a and 22b, are 30 Resistor 29------330 ohms, required in the system. These give high impedance to the Capacitor 30------22 microfarads. passage of audio signals from coil 9a to D.C. signal and/ or control voltage circuit 18, and from coil 19b to D.C. Whereas this invention is here illustrated and described signal and/or control voltage circuit 20, respectively. with respect to a specific embodiment thereof, it should Were choke coils 21a and 21b not included, there would be realized that various changes may be made without de be excessive induction power pickup of audio signals in parting from the essential contribution to the art made by coils 19a and 19b and dissipation of audio signal power the teachings hereof. in the respective D.C. circuits 18 and 20, I claim: The particular D.C. signal and/or control voltage cir 1. In a signal combining, conveying, and then signal cuit 18 is shown to have a normally open manually con 40 separating system having a common voltage potential ref trolled Switch 23 connected between ground and the base erence Source and with conductor transmission line means of NPN transistor 24. The emitter of NPN transistor 24 interconnecting two electronic component stations: a con is connected to ground while the collector is connected ductor transmission line; audio signal transmitting trans through choke coil 21a to the coil 19a of transformer formers in each of said electronic component stations; 14a. A positive voltage supply 25 of, in a working em each of said transformers including a first coil winding bodiment, between approximately 22 and 28 volts is con 45 connected to audio circuit means; a second coil winding: nected through resistor 26 to the collector of transistor of each transformer being interconnected at the corre 24 and through a voltage divider including resistors 27, sponding ends through said conductor transmission line; 28, and 29 to, from the junction of resistors 28 and 29, each other end of said second coil windings being con the base of NPN transistor 24. A capacitor 30 connected nected through, a capacitor to the voltage potential ref from the junction of resistors 27 and 28 to ground in co 50 erence source; D.C. circuit means at each of said elec operation with resistor 27, of the voltage divider, insures tronic component stations; each transformer being pro reduction to a negligible level of any audio signal origi vided with a third coil winding; each of said D.C. circuit nated components impressed on the base-to-emitter volt means being connected through said third coil winding of age of NPN transistor 24. Furthermore, choke coil, 21a the respective transformer to the common junction of said reduces residual ripple signal to a minimum level and sub 55 second coil, and said capacitor of each station; and with stantially prevents any such ripple signal from being said second and third coil windings of each transformer Superimposed upon the audio signal being inductively having such polarization that D.C. current flow through transmitted through transformer 14a. On the “b' side of the second coil winding is opposite in direction to D.C. the System coil 19b of transformer 14b is connected current flow through the companion third coil winding. through choke coil 21b to the base of NPN transistor 31. 60 2. The signal combining, conveying, and then separating The emitter of NPN transistor 31 is connected to ground system of claim 1, wherein said second and third coil While the collector is connected through a relay coil 32 of windings are bifilar wound in each of said transformers. a relay 33 to a positive voltage supply 34 which not only 3. The signal combining, conveying, and then separating Serves to Supply relay actuating power but also collector system of claim 2, wherein said second and third coil biasing voltage power for NPN transistor 31. Relay 33 65 windings have substantially the same number of turns. may have a drive connection 35 to audio output/input 4. The signal combining, conveying, and then signal circuit 11b, as, for example, a push-to-talk actuating relay separating system of claim 1, wherein a choke coil is pro and/or for other D.C. signal controlled functions, as vided in the connections between the respective D.C. cir desired. cuits and said third coil of each respective transformer. With reference to the D.C. switching operation with the 70 5. The signal combining, conveying, and then signal D.C. signal, and/or control circuits 18 and 20 in trans separating system of claim 1, wherein said transformers mission system, 10, transistor, 24 is normally forward are toroid core type transformers. biased well into the saturation region so that the collector 6. The signal combining, conveying, and then signal to-emitter voltage of transistor 24, in the saturated state, is 75 separating system of claim 1, wherein said audio circuit 3,328,527 S 6 means of one of said electronic component stations is an cludes D.C. signal generating means; and said D.C. cir audio input circuit connected to said first coil winding as cuit means of the other electronic component station in a primary coil of the audio signal transmitting transformer cludes D.C. signal utilizing circuitry. of that electronic component station; the audio circuit 8. The signal combining, conveying, and then signal means of the other electronic component station being an separating system of claim 7, wherein each of said audio audio output circuit connected to a said first coil winding circuit means are combination audio input and audio out as a secondary audio output coil winding of the audio put circuits. signal transmitting transformer of the other electronic References Cited component station; and with said conductor transmission line being a single conductor transmission line intercon UNITED STATES PATENTS necting an end of one of said second coil windings with O 942,208 12/1909 Kitsee ------178-58 the corresponding end of the other of said second coil 1,251,208 12/1917 Ferriter ------178-59 windings. 7. The signal combining, conveying, and then signal JOHN W. CALDWELL, Primary Examiner. separating system of claim 6, wherein the D.C. circuit 5 J. T. STRATMAN, Assistant Examiner. means of one of said electronic component stations in