April 14, 1959 2,882,339‘ P. G. SMEE EI'AL PASSIVE CONFERENCE CIRCUIT Filed Sept. 20, 1955 FIG.|. F TnHvE0A0N w 0MPTR 22GT ML“ 2, __0“MN F Tmnu.| MumELMSIETN GTv CE2 N LJIIIm:P8C |852 m RGTTH. NA3.AQ H1|IV I2IT O R UMNWRN GN|IlFT|L_E NmSEM GMMWE. TlNU m FS m. ZN _ mm NM\TR A LL W :M._ /5.“ \u _‘ __GmN D _ _ Tv A_ _ _ _ _ _ _ ‘ M T2 _ R w. M _ ~ _ w_ _ _ _ _ . , a _ ._ 7.. _ _ TO _3 _ 1RT R A. INVENTORI JAMES S. S. KERR BY i / HIS 7 "ice ' 1 2?... transmittters, respectively, in a manner minimizingiiata tenuation. Our invention'will'be better‘ understood! from the fol lowing description taken in connection with the accom panying drawing and its scope will be pointed out in the appended claims. 2,882,339' PASSIVE CONFERENCE CIRCUIT Peter G.‘Sn1ee, North Syracuse, and James S. S. Kerr, Syracuse, N.Y., assignors to General Electric Company,‘ In carrying out our invention‘ in one form th'ereofj?ve‘ a corporation of New York Application September 20, 1956, Serial‘No.r610,980 - 14 ‘Claims. (c1. 179-1).‘ 2,882,339 Patented Apr. 14, 1959 transmitters are conne‘cted'in aclos'ed series loop. . Each of these transmitters has‘ an‘ associated receiver which is‘ 10 connected" in rparallel'racross'lthe two transmitters? mostfire mote in ‘the 1-.loop' from vfits associated transmitter; The" transmitters ?and' receiverszareso designed as .to present substantially equal .im-peda'ncess’ato the ‘:network. so‘. that during operation of any one of ‘the transmitters? af'null This invention relates to passive conference circuits 15 condition will exist across its associated receiver with re and more particularly to passive conference circuits de spect to the signal transmittedi‘for any passive operating signed for minimum attenuation of desired signals: and condition. minimum power loss; In the drawings, It is well known. in the prior art to utilize impedance Fig. 1 is a schematic circuit‘ diagram of one form of networks having passive elements‘ inforder to intercon 20 our invention; nect more than two transmitter-receiver sets in a confer~ Fig. 2 is a passive network having six sides; and ence circuit. The majority of the prior art circuits, in Fig. 3 is a block diagram depicting a circuit in which order to reduce cross-talk, operate on the principle of Fig. l is employed. attenuating the transmitted signal from a particular trans; Referring to Fig. 1, it? ‘can be- seen thatt?ve' transmitters, mitter when it appears back across‘ itsv associated receiver 25 designated as T1, T2, T3, T4, and T5 are connected in a to a greater degree than it is‘ attenuated when it is trans mitted to the remainder of the receivers in- the network. closed, series loop; Five’ associatedreceivers, designated as R1, R2, R3, R4, and R5 respectively, are shown con This type of treatment of the problem results in‘ fairly nected in parallel with the two transmitters most remote large total power loss in the-‘circuits employed and at in the loop from the transmitter ‘associated with each re the same time does not completely eliminate cross-talk.‘ 30 ceiver. For .examplepR'l- is connected] across; transmitters In many circuits it is necessary to provide further ampli T3:,and_.T4,»_which are the-two transmittersmost remote ?cationiof the signals to offset the attenuation resulting intth'e loo‘ptrom. transmitter: Tp, E?Ch'ZOf. these trans. from the attempt to eliminate crossetalk. ~ This vadds mitters and receivers is designed to present substantially’ bulky and expensive‘ active elements to the passive ele equal impedances to the networkv for any passive operat ments employed. 35 ing‘ condition. Itis also known in the art, where it is desired to in If transmitter T1 is energized so that the potential at terconnect three transmitter-receiver sets, to employ a point 10 is plus one volt and 'the‘ potential'at point ‘11 Y-delta type of connection wherein the transmitters are is ‘minus one'volt,‘then'the-potential-at points-12', 13; connected in “delta”. and their associated receivers are‘ and 14 will be zero volts, since eacheofv'the'sekpoint‘sl lies connected in-Y from the corners of; the .“delta” or vice‘; 40 on the center of a potential divider between the points versa. Each. receiver is connected to the: corner of the 10 and 11, the remainder of the .circuitalso being sym “delta”-connected transmitters opposite‘ to‘ that of its as'-' metrical. Since "the"points"12‘,* 1'3, _and"14 are at the sociated transmitter. This‘typeno'f systemtpresents a null same potential, or.zero¢.volts,.no current will flow in re condition. acrossszthe receiver associated With-the trans; ceiver R1 or transmitters T35 and T4. Equal currents will mitter. which‘ is=~transmitting at any‘v particular time for. 45 ?ow from the point 10 to the point 12 to the point 11, any passive operating condition. from-‘the fpoint'i 101" to ~ the-point 113i- to-theipoint; 11. and‘ A- problemv long existingin the art has been to: con from the point 10 to the point 14 to the point 11, since‘ nece morethan three transmittererec'eiver- sets‘ in a man; ner which would‘ not attenuatev ‘the. transmitted‘ signals‘ the impedances of .- these parallel branches are equal. These currents are illustrated: in the'drawing as I1, 12, and objectionably and whichwo'ul'd at the 'sam'etime elimi= 50 I3 respectively. The remaining receivers R2, R3, R4, and R5 will be actuated equally'by' transmitter T1. Also cur associatedreceiver; The existence of. this-problem is ap rent will ?ow in transmittersiTz" andTE and therefore ad parent. when we consider the. large number/of intercon ditional power will bedissipateds nection circuitsaemploying‘ modi?cations ‘of the. attenua-u In the method of operation described, transmitter T, tion principles previously discussed. Accordingly, itrisi 55 presents a'null condition‘ across-"receiver'Rl. This null an object of our invention tov provide a passive confer condition arises "in v‘branches which?’ will be hereinafter ence circuit employing more‘ than three transmitter-re referred toi'as “conjugate branches. This transmitter and ceiver sets in which attenuation is minimized and cross its‘ associatedt're'ceiver in conjugate branches form ‘what. talk substantially eliminated. _ is‘calle‘d "a transmitter-receiver‘ or T-R' pair. The attenu It is another object of our invention ‘to achieve the 60 tion of the'network can bederivedi as follows‘. Attenua‘ above-delineated results utilizing a minimum number of tion‘in' decibels'is-‘equal' to ten times‘ the‘ logarithm‘ to components and connections. the‘base'tenof the ratio of the power of the transmitter Still another object of our invention is to provide a to*the‘~‘power dissipated in' a particular'receiver, or nate cross-talk between a particular transmittenandfitsi novel passive conference network inwhich' as many as ?ve or more transmitter-receiver sets‘ may be connected. 65 A further object of our invention is to provide a novel circuit wherein any transmitter-receiver set may be re placed by .7 equivalent - dummy, impedances, , when .this transmitter and receiver are not to be used,v inorde'nto. maintain a balanced, symmetrical network. 70 A still further object of our "invention is to connect one transmitter or one receiver to a group of receivers or a=attenuationinrdb ’ Piji==p0WBT deliveredaby aztra‘nsmitt‘en' ' Pg=powenfdissipationin aisingler receivers‘ _ _ 2,882,389 4 3 symmetry of the network and yield the same operating The voltage across a transmitter is twice that across characteristics as if all transmitters and receivers were in any single receiver and the current thru the transmitter is three times that thru any receiver so the power ratio becomes ~ ' ' s - ' ____________=3v ERIE ‘ use. ' It is apparent from the symmetry of the network that the network is not limited to the mode of operation de scribed above wherein the points 10 and 11 require equal and opposite potentials. These values have only been used as a convenient example. If, for instance, the point 10 1 (2) where ER=the voltage across a receiver IR==the current thru a receiver were at zero volts and the point 11 at two volts, the Additional power loss occurs due to the inability to points 12, 13, and 14 would each be at one volt and again no current would ?ow in receiver R; or transmitters T3 and T‘. These conditions exist for any voltage value across transmitter T1. achieve optimum conditions. Taking the transmitter im pedance as R the total impedance of the three parallel vides a convenient passive conference circuit in which ET=2ER, the voltage across the transmitter IT=3IR, the current thru the transmitter branches across the transmitter is %R. The power to the load is ‘ It can be seen that the network described above pro a minimum number of elements and connections are nec ' P1t=FRa essary and a minimum amount of attenuation is experi (3) . enced. _ Turning now to ,Fig. 2 there is‘ shown an alternative where R, is the equivalent load impedance. We then 20 embodiment of the invention in which the connections form a six sided polygon having all the diagonals con~ nected. In this ?gure the transmitters are again designated have: " V 3 . T1 through T7 having associated receivers R1 through R; respectively. In order to achieve the desired null at a = given receiver when its associated transmitter is transmit~ R2 . $____. V <R+Ro= ting, the connections are made as shown. > Taking a partial derivative we get [email protected]_ 1 __ 2R, Matias-Roz (RTE-iii (5) ._ R_____R2 1 Three T-R pairs are connected each with its respective transmitter g- and associated receiver on opposite sides of the polygon. Three T-R pairs are connected each with its respective 30 transmitter and associated receiver on opposite minor diagonals as shown. The remaining pair is connected to (5) twov of the major diagonals. Dummy impedance D, is When Equation 51 is equated to zero, we have the condi tion for optimum power transmitted to the load, and this '_ connected in the other major diagonal in order to com "(R+Rr)‘ plete the symmetry of the circuit. This dummy imped ance will cause some additional power loss. occurs for R=R,. Putting this condition into Equation 4 we obtain ' Again as in the circuit of Fig. 1 a signal transmitted from any of the transmitters will appear as a null across its associated R V2 T129271? , e (6) : receiver. However, in addition the signal from transmit ter T; will not be received on receiver R2. It may not be ' This yields the optimum power and the attenuation 40 desired to use the seventh set. For certainapplications in which it is desired that at ?gure must account for the di?erence between this and tenuation be reduced, it may be desired to connect a single the actual power. Now, transmitter to a group of receivers or vice-versa. This Va may be done using our interconnection circuit by position P optimum_ 47R____2_51 (7) 45 ing the transmitter element and then locating receiver ele P actual _ V2 ‘24 ments at all or most of the points or in all branches of the 2 22R circuit which do not receive a null signal from a voltage ‘‘ generated in the branch where the transmitter is located.‘ (Mm) "3 Thus the attenuation of this network in decibels is equal to The remainder of the branches may contain dummy im 50 pedances, but still the attenuation is less than that nor mally experienced by using a separate padding impedance with each element, as is conventionally done when im 1 pedance matching is desired and all the branches are paralleled. =10 logio 6.25 = 10 X .79588 55 =7 .96 decibels The teachings of our invention can be readily extended to a series of regular polygons with all of the corners connected together by diagonals. A generalized expres ? sion for this is This amount of attenuation, including that due to mis match, is not large enough to seriously hamper the opera tion of the network and is considerably less than attenua 60 tions of 15 db or more experienced in the passive circuits where d is the total number of diagonals and n is an in-. of the prior art employing ?ve or more sets. It is obvious that if we desire to place matching impedances in the 1 teger de?ning the number of sides of the polygon. Also, network, so that for instance a transmitter or receiver. would always see 600 ohms looking in, additional attenu 65 ation would be experienced. ~It is desirable to do this, 'for example, when standard transmitters and receivers are employed which are best matched at 600 ohms or n2 —n _ 2 where b is the total number of branches involved. The v number of major diagonals is some other predetermined value. In the event that fewer than ?ve people wish to confer 70 on the conference circuit, dummy impedances, substantial-, ly equal to the transmitter and receiver impedances em ployed, may be inserted in place of the transmitter and receiver elements at the points in the network which are desired to be made‘ inoperative- This will preserve the. 2 P, the number_of conjugate pairs of branches, cross-i , coupled, equals b/2 for small :1 for even b and b--1 2 . 2,882,339 0 6 for odd b up to n=7. For n=8 or larger p is.l~2n--3 1. In combination, a plurality of transmitters in excess of three each having an associated receiver, means elec The impedance in each branch, .Which is. equal in.v all branches, is trically connecting said transmitters and receivers in'sep: where Z0 is the desired operating impedance‘ (in andiout) polygon withall diagonals joined, any of said transmitters and its associated receiver being connected in conjugate arate branches vof a _circuit,-said circuit de?ning a closed branches of said circuit, the branches in which'said con nections are made including both said diagonals and the and Z, is the series impedance for each pair for a desired Z0. The impedance looking into any branch is» 2Z1, Zr=,,—J sides of said polygon, whereby during operation of any 10 one of said transmitters it will present a null condition across its associated receiver. 2. In combination, a plurality of transmitters in excess of three each having an associated receiver, acircuit elec trically connecting said transmitters and receivers in sep: 15 arate branches of a closed polygon having all diagonals joined, any of said transmitters and its associated receiver When voltage is applied across one branch the number being connected in conjugate branches of said circuit, the of active branches across which an output voltage. will ap branches in which said connections are made including pear is b,,=2n~—4. The number of. passive branches is both said diagonals and the sides of said polygon, where 20 by during operation of any one of 'said transmitters it will 2 be _ also, Jfi’L?L, present a null condition across its associated receiver. and where r is the number of redundant branches. The out equally activate the remaining receivers. put voltage is 3. In an intercommunication system havingv ?ve trans mitters each having an associated receiver, a circuit elec~ Et 25 trically connecting said transmitters and receivers, said E,,_-§ circuit comprising a pentagon having all diagonals joined, where E is the input voltage. The attenuation due to mismatch correction in decibels is 2 any one of said transmitters and its associated receiver being connected in conjugate branches of said circuit, the branches in which said connections are made including 30 both said diagonals and the sides of said pentagon, Where by during operation of said one of said transmitters it will and the total attenuation am=2ol0g1o from the input to the‘ output is present a null condition across its associated receiver and 06;:20 log“, equally activate the remaining receivers. 4. In an intercommunication system having at least?ve 1 transmitters each having an associated receiver, a circuit Optimum characteristics of attenuation are achieved ‘in electrically connecting said transmitters and receivers in separate branches of a closed polygon having all diagonals the con?guration shown in Figure 1 where there are no unusable or redundant branches‘. Turning now to Fig. 3 where we have described the use joined, any one of said transmitters and its associated re ceiver being connected in conjugate branches of said cir cuit, the branches in which said connections are made in cluding both said diagonals and the sides of said polygon, whereby during operation of said one of said transmitters of the con?guration of Fig. 1 in microwave equipment the pentagon having all diagonals connected, hereinafter called the pentastar 15,‘ can be seen in the center of the ?gure. This pentastar interconnection is similar to that it will present a null condition across its associated re illustrated in Fig. 1. Surrounding pentastar 15 are four T-R pairs 16, 1'7, 18, and 19 which are connected to con 45 ceiver and equally activate the remaining receivers. 5. In combination, ?ve transmitters each having an as jugate branches of the pentastar 15, in the manner herein sociated receiver, said transmitters and receivers each before described, the speci?c connections not being shown having substantially equivalent passive impedances for in Fig. 3. Obviously then, one pair of conjugate branches any operating condition, a circuit electrically connecting of pentastar 15 will contain dummy impedances for this circuit con?guration. T-R pair 16 is connected to local 50 said transmitters and receivers in separate branches of a pentagon having all diagonals joined, any one of said phone 26. T-R pairs 17 and 18 are shown leading to transmitters and its associated receiver being connected “West” and “north” channeling equipment respectively. in conjugate branches of said circuit, the branches in This equipment is shown in block form associated with which said connections are made including both said T-R pair 19 in the “east” channeling equipment 23, which consists of a modulator and demodulator 24 and 25 re 55 spectively, leading to and from the T-R pair 19 through appropriate circuitry to the antenna 26. A signalling matrix 27 is also shown connected to T-R pairs 16, 17, 18 and 19 to provide for ringing respective associated channels. 60 It can readily be seen that by selecting a proper value of n, in the foregoing equations, any number of T-R pairs and associated channeling sets of equipment may be diagonals and the sides of said polygon, whereby during. operation of said one of said transmitters it will present a null condition across its associated receiver and equally activate the remaining receivers. 6. In combination, ?ve transmitters each having an as sociated receiver, said transmitters being electrically con— nected in a closed series loo , and each of said receivers being electrically connected in parallel across the two transmitters most remote in said loop from the trans mitter with which it is associated whereby during opera utilized in a circuit of this nature. Also it is obvious that the positions of the transmitters and receivers could be re 65 tion of any one of said transmitters it will present a null condition across its associated receiver and equally acti versed in all con?gurations and that certain of the trans mitters could be replaced by receivers or vice-versa. vate the remaining receivers. 7. In combination, ?ve transmitters each having an as sociated receiver, said transmitters and receiver each hav While we have shown particular embodiments of our invention, it will be understood, of course, that we do not wish to be limited thereto since many modi?cations may 70 ing substantially equivalent passive impedances for any be made, and we therefore contemplate by the appended claims to cover any such modi?cations as fall within the true spirit and scope of our invention. What we claim as new and desire to secure by Letters Patent of the United States is: operating conditions in order to minimize attenuation, said transmitters being electrically connected in a closed series loop, and each of said receivers being electrically con nected in parallel across the two transmitters most remote 75 in said loop from the transmitter with which it is associ 2,332,339 7 8 ated whereby during operation of any one of said trans providing connections between any transmitter and its associated vreceiver whereby during operation of any one mitters it will present a null condition across its associated receiver and equally activate the remaining receivers. of said transmitters it will present a null condition across 8. In combination; a closed series loop of ?ve elements consisting of at least two transmitters and the remainder of dummy impedances, each of said ?ve elements having an associated element; said associated element associated with each of said transmitters being a receiver and said associated element associated with each of said dummy its associated receiver and a signaling matrix connected to each transmit-receive pair associated with said channel~ impedances being a dummy impedance; said transmitters, 10 circuit for said elements and said conjugate elements, said receivers and dummy impedances each presenting an equivalent passive impedance to the combination; and each of said associated elements being electrically con circuit forming a closed polygon of greater than four sides having all diagonals connected, said elements and their respective conjugate elements each being connected in a separate symmetrical conjugate branch of said circuit so ing equipment for selectively ringing a desired channel. 11. A combining network for reducing attenuation com prising a group of elements in excess of four, a conjugate element for each element of said group, an interconnection nected in parallel across the two of said ?ve elements most remote in said loop from the one of said ?ve ele 15 that a voltage generated at any element will appear as a null across its associated conjugate element and dummy ments with which it is associated, whereby during opera elements connected in any remaining branch of said cir tion of any one of said transmitters it will present a null cuit in order to complete the symmetry thereof to estab condition across its associated receiver and equally acti lish conjugacy relationship. vate the remaining receivers. 12. A combining network comprising a closed polygon 9. A microwave communication circuit comprising in 20 having at least ?ve sides, said polygon having all its combination, a local phone for transmitting and receiving diagonals connected, a separate circuit element connected connected to a transmit~receive pair, a plurality of sets in each branch of said network, said circuit elements com of channeling equipment in excess of two each connected to a transmit-receive pair, a circuit connecting said trans prising a plurality of symmetrically conjugate pairs having providing connections between any transmitter and its as sociated receiver wherebyduring operation of any one of said transmitters it will present a null condition across its associated receiver. 10. A microwave communication circuit comprising in a null across its conjugate and the attenuation due to inter 13. The network of claim 12 in which one of said ele ments is a transmitter, the remaining elements and con connected to a transmit-receive pair, a plurality of sets of channeling equipment in excess of two each connected to 14. The network of claim 12 in which one of said ele ments is a receiver, the remaining elements and conjugate mit-receive pairs, said circuit comprising a closed polygon 25 substantially equal passive impedances and the remainder of dummy impedances equal to the passive impedance of with all its diagonals connected, each branch of said cir each element of said pairs, said conjugate pairs being con cuit containing either a transmit or a receive part of said nected in conjugate branches of said network whereby a pairs or an equivalent dummy impedance, said pairs being voltage present at one element of said pairs will appear as located in symmetrically conjugate branches of said circuit connecting said elements will be minimized. jugate elements comprising receivers and dummy combination, a local phone for transmitting and receiving 35 impedances. elements comprising transmitters and dummy impedances. a transmit-receive pair, a circuit connecting said transmit receive pairs, said circuit comprising a closed polygon with References Cited in the ?le of this patent all its diagonals connected, each branch of said circuit 40 containing either a transmit or a receive part of said pairs or an equivalent dummy impedance, said pairs being lo cated in symmetrically conjugate branches of said circuit UNITED STATES PATENTS 2,035,536 Cowan ______________ __ Mar. 31, 1936

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