NNw 0A0 TnHvE TNN SIE ELM Mum N 7

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