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July 7, 1959
' G. ELLIOTT
' 2,894,074
TELEPHONE ` CONFERENCE CIRCUIT l
Filed Feb. 25," 1955
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July 7', 1959
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Filed Feb. 25, 1955
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G. ELLIOTT
TELEPHONE CONFERENCE CIRCUIT
Filed Feb. 25, 1955
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Filed Feb. 25, 1955
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July 7, 1959
G. ELLIOTT
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Filed Feb. 25, 1955
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Filed Feb. 25, 1955
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G. ELLIOTT
2,894,074
TELEPHONE CONFERENCE CIRCUIT
Filed Feb. 25, 1955
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11 Sheets-Sheet 9
July 7, 1959
G. ELLIOTT
2,894,074
TELEPHONE CONFERENCE CIRCUIT
Filed Feb. 25, 1955
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2,894,074
G. ELLIOTT
TELEPHONE CONFERENCE CIRCUIT
Filed Feb. 25, 1955
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2
another rate of speed while making and breaking a cir
cuit including the output of a ringing generator. The
rate of speed of the relay is switched responsive to the
second of the two registration motions of the selector
switch. In this manner a busy tone signal is given at
2,894,074
TELEPHONE CONFERENCE CIRCUÍT
George Elliott, Rochester, N.Y., assignor, by mesne as
most stations while ringing current is provided at a called
station.
signments, to General Dynamics Corporation, a cor
.
Certain special features are also provided.
poration of Delaware
For ex
ample, the selector may seize either a dial switching
exchange, or a cordless P.B.X exchange, either of which
may be used to extend the call further. The P.B.X is
'Application February 25, 1955, Serial No. 490,582
12 Claims. (Cl. 179-41)
provided with a bright-dim supervisory lamp which glows
brightly when an unanswered call is on a local line,
This invention relates to microwave radio link tele
phone systems, and more particularly to selector switches
and conference cal-l systems for use in microwave radio
glows dimly during a conference call, and is extinguished
for on-hook supervision.
An all-transistor ampliñer is used to provide negative
impedance to compensate for the number of stations
link or carrier terminals.
Recently, microwave radio relay networks have re
that are added in a conference call.
These and other objects will be obvious to those skilled
placed pole line construction in many instances. One of 20 in the art from the following description of the accom
panying drawings in which:
the characteristics of a microwave network is that it must
have repeater stations located at spaced intervals along
Fig. 1 shows a block diagram of how the system may
the length of the system. This characteristic also coin
be connected together, the heavily inked boxes being an
indication of those portions of the system which are
cides with that of certain special type maintenance, com
munication, control or other systems, such as is found 25 shown in detail in the accompanying circuit drawings;
on toll roads, for example. That is, a characteristic of a
Figs. 2 and 3 show a dial station selector switch;
Figs. 4 and 5 show a dial trunk selector switch;
toll road network is to provide toll houses, police sta
Fig. 6 shows an adapter circuit and part of a cordless
tions, maintenance crews and the like which are distrib
P.B.X circuit; ywhile
Therefore, it is economical to use a microwave network 30 P Fiìgçs. 7, 8 and 9 show the remainder of a cordless
wherein each repeater station is provided with means for
Fig. 10 shows an all-transistor amplifier designed to
serving a toll house, a maintenance establishment or other
provide a negative impedance characteristic to the con
location. In this case, a considerable saving of time
and personnel may be had if the telephone network is
ference call circuit;
uted at intervals along the length of the road system.
arranged on a dial basis so that any subscriber may dial 35
Fig. 1l shows a skeletonized conference call circuit
and speak with any other subscriber.
taken from the detailed circuit shown in Figs. 2-10;
It seems obvious that it is also necessary to provide for
Fig. l2 shows an electrical equivalent of the conference
call circuit with all circuit elements lumped; and
a plurality of subscribers at some central location, as by
means of a private branch exchange (P.B.X), for ex
Fig. 13 shows the manner in which Figs. 2-10 should
ample. On occasions both the radio link subscribers and 40 be arranged to provide a complete and operative circuit.
the P.B.X subscribers may want to establish a conference
In the drawings, the otlîice potential is shown by means
call involving a plurality of subscribers. On calls of this
of simple plus and minus signs. As is the case in most
type ~the signal current drops-off rapidly as each telephone
telephone systems, the positive terminal is described as
is added in the conference call circuit. It is necessary to
connected with ground; therefore, the terms “ground
provide some means for compensating for this drop in 45 (-{-)” and “(-) battery” have been used throughout the
signal current if satisfactory service is to continue. One
speciiication. It should be understood that either this or
method of compensating is to amplify the signal current
any other suitable system may be used.
while another method is to use an amplifier to provide
BRIEF DESCRIPTION
gain for a derived signal which may then be fed back
Fig. l shows generally a microwave radio link tele
into the conference call circuit in a manner which eiîects 50
phone system using the subject invention. In this drawing
the impedance characteristics of the circuit. This is called
“negative impedance.”
a number of subscribers are connected into a system
An object of this invention is to provide a bright-dim
supervisory lamp in a cordless P.B.X.
using a plurality of radio channels, wherein each channel
Yet another object of this invention is to provide a. '
provides one “party line.” For example, channel 1 serves
subscribers A-G. An electromechanical switch is pro
new and improved conference call circuit.
Another object of this invention is to provide means
including a negative impedance to compensate for the
vided at each terminal serving one channel so that any
loss of signal occasioned by the addition of subscribers’
of channels terminating, such as at cordless P.B.X 116,
60 for example, a switch is provided for each channel.
sets in a conference call circuit.
These objects are accomplished in one form of the
subject invention by means of a single motion selector
switch which is operated to register a iirst digit of a
called number, to drop-back, and then to reoperate to
register the second digit of the called number. Respon
sive to these two registration motions of the selector
switch, means is provided for selectively signalling one
subscriber may dial to signal any other subscriber on
that channel.
In the case where there are a plurality
Specifically, each radio channel is shown by a plurality
of antennas representing microwave terminals or repeater
stations. Each microwave terminal may include multi
plexing equipment such as modulator M31, and demodu
lator D31 while any suitable four wire terminating set,
such as hybrid circuit H31, may be utilized to inter
connect conductors T and R with modulator M31 and
demodulator D31. Special radio link equipment M32
may be provided to transmit and receive radiant energy.
microwave channel.
A self-interrupting relay is provided to operate at one 70 For example, signals to and from station A are trans
mitted and received over antenna 102. The next micro~
rate of speed while making and breaking a circuit includ
wave repeater sends and receives signals at antenna 103
ing the output of a tone generator and to operate at
of the subscribers who then may talk over the common
2,894,074
4.a
3 _
as subscriber B or C (Fig. l), for example. Subscriber
A initiates a call by removing ,his receiver thereby com
pleting a loop across tip and ring conductors T and R
to and from antenna 102 while repeating these signals
from antenna 104 to antenna 105. In a similar manner,
the next repeater is served by antennas 105 and 109, etc.
(Fig. 2), in a conventional manner. Responsive thereto,
calling bridge relay 240 operates over the circuit from
The equipment shown tothe left-'of cordless P.B.X »116 «
comprises- one “party line” channel-while the equipment
shown to the right of the cordless P.B.X comprises an
other “party line” channel. Each of these repeateror ter
minal stations is provided with suitable microwave, multi
plex, signal and switching equipment.
ground (+), through the upper winding of relay 240,
rest contacts 212, conductor T, telephone A, rest contacts
214, and vthrough 'the lower- windingi -of-=calling«.-~` bridge
relay 240 to (_) battery. Calling bridge relay 240
For - example, if »
subscriber A should call another subscriber on his channel; i 10 operates».
Thisv relay is used -to yfurnish ltalking-battery»,ï
to detect and signal the presence of a call ,and to'respond
signal equipment S31 responds to subscriber A trans
mitted digit pulses to step simultaneously. dial selectors
107, 114 and corresponding switches at each~other
repeater' station on the same: channel.
to and repeat digit pulses. Responsive tothe operation
of calling bridge relay 240,"contacts 241~close-to operato
send relay 390 over the following circuit: (_) battery
through the windingv of send Yrelay390-,”'operated pulsing
contacts 241, resting contacts 361 and 329 to ground ( -}-).
One. selector -,;
encounters suitable markings indicatingthatfthe called
subscriber is at. that repeaterv stationçztherefore-a >suitable
ringing or other circuit, inuthe caseof -sx.\bscrib'er;.E,- is4
The purpose of this relay is to signal the distant terminal
by way of` anysuitable signal.,equipmentRS3l.~ More
particularly, »relay 39,0 is used .atl this` .timelto ,close Y.conmv
completed to signal the called subscriber; or,'=inl the case »
of subscriber B, additionalswitching maybe completeddn
dial exchange 108 responsive »to furthersdigit pulses trans
tacts’391 thereby'transmittingza seizure sigria1.._,Returning_`I>
to
close
the to
operation
complete
of calling
an obvious-circuitfor
bridge relay 240,.releasedelay
contacts242
mitted from substation A. In thefcase, of calls to sub
scriber C, an operator at cordlessaP.B.-X 116 ‘completes
the call. The selectors which did not encounter a marking
relay 250. The primary purpose_.,of this..relay._vis».to.:
furnish master ground at contacts' 257 andthereby hold. _:
indicating that the called party is atfits particular micro
the circuit operated when calling bridge. relay 24_0.releasesvv
wave repeater or terminal remain ,inV their operated
during dial: pulsing.
position until the end of the-call; meanwhile, signal equip
ment at all other stations is locked so that no otherl
subscriber may dial into a busy channel:
Selectors 100, 107, 114 and 119 are similar. Switch'100
can only signal a subscriber station while switches _107, 30
114 and 119 may transmit any one of various signals
depending on the particular equipment being called in..
ReleaseY delay relay 250 operates.-- Itcloses its contacts.`
257 to connect ground.(-i-) to master, ground conductor..
MG. This conductor is called “mastenground’î because..
it furnishes the ground- marking „bymeanstof :which-m
most relays in selector 100 >are >held in anoperated posi-,_
tion. This ground also starts tone .generatonTG-Zl viaÍ
theV “start” conductor. Dialtone generator '.TG21 pro-„f
duces a vtone eurrent'which-Í is.,now .connected throught.4
In each case the talking conductors are equivalent to
“party line” connections and are not switched.
Each of the dial station selectors is provided with a 35 operated contacts 251, restcontacts 341,Í 321, >capacitor
two speed self-interrupted relay, such as relayv230, for
C31, contacts4 212,. subscriber. A’s telephone„ restcon
example. This relay is connected in series with a resistor
and a capacitor. At one time relay 230 operates at a
tacts 214, and the llower winding of calling bridge relay ,
cause the relay to operate at a relatively low rate of speed
to provide an interrupted ringing current. The rate of
372 thereby> `connecting . .the output , of ~demodulatorl lD31
240 to (__) battery. Contacts .253.close to complete.,
a circuit via contacts 32310 yoperate .switch.relay._370._
relatively high rate of Vspeed to provide an interruptedl
busy tone. At another time the resistor is shuntedto 40 The purpose of this relay ,isf to'close contacts 37.1.and
to thevk hybrid coil and.A balancing networkv H31;Y
Normally, these contacts` areropen ,whentheftalkingn
circuit is not in use, thereby preventing any ¿unduehowling _.¿
dial station selector 100 to seize an idle line.
Conference calls are completed by the intervention of 45 or singingin the carrier circuit.
speed of the relay changes responsive to the operation of
an operator who is served by telephone 117. In the case
of calls of this type, an unbalanced conference amplifier
117a is connected by choke coil CH101 to a balanced
conference call circuit in cordless P.B.X 116. This
Permanent- ltímìng.--Contacts 254-close .to prepareithe .
permanent timing device which .releases thedistant: equip?,
ment if digit pulses are not transmitted promptly. More.:v
particularly, ground (-1-) is-extendedr-through contacts.;
amplifier is adapted to provide a negative impedance 50 254, 325, .342,- 363 and» resistor: R-31f,-t0..-(--) fbattery.,
characteristic which is used automatically to olf-set the
Resistor-.R31 heats over a.given.«time periodto-a sufficient-z
added impedance of each telephone as it is added to the
conference call circuit.
DETAILED DESCRIPTION
Figs. 2-10 show details of circuits shown in Fig. l
by heavily inked boxes. For example, dial selector 100
is shown in Figs. 2 and 3, while trunk selector 114 is
temperature to close contacts #RSL-,tocomplete a circuit.
for permanent-.timef-relay 360.’- Thisfcircuit extends from..l
contacts
(_ ) battery
R32,`through
rest contacts
»the winding=§of~
342, 325‘and
relayLy25410
360,- operated
ground»y
55
(-1-). When relay-360«operates;.»it.locks1fover. a'circuit
including contacts 362.`l Contacts~~361 Vthen. open thereby»`
breaking 'the holding, circuit for send- Arelay¿¿390.-.y This
shown in Figs. 4 and 5. Trunk selector 107 is the same
circuit formerly included \contactsw241,¿361tand-329.,
as vthat shown in Figs. 4 and 5 Vexcept that the dotted 60 Release vof sendl relay »390 terminates the` seizure signal-,to
rectangle marked “Dial Exchange” 108 is used andadapter 115 is omitted.
STATION SELECTOR 100
The circuit of Figs. 2 and 3 shows a two-digit station
the distant microwave terminal, ,thereby-releasing im
Assuming, however, that> digit.,> pulses.Á are -,receivedf,be-,~4v
fore the expiration of the predeterminedí timeìperiod~.re-.-quired " for. resistor R31 - to': heat suñicientlyrto ,fclose
Briefly, each’ 65 contacts R32, contacts'l 342ifopen >in the manner-Amber;
explained.` ‘below in ftheg. section :entitled _“Dialingà’ This@y
selector is arranged with a single pair of talking con
in
.turnfprevents the operation fof Ipermanent time-„relayv
du'ctors to which its associated station is connected.
360.
There is no switching between various tip and ring
Dialing-The fcircuit isv now.L prepared for :thee-receiptr;
conductors. The selecting‘motion of the switch deter
selector for a radio or carrier terminal.
mines only which one of the possible called parties is 70 of digit pulses;y therefore,-:»nothing;,furthen.happensl until.;A
callingy subscriber AVv transmits afsuitable number v_of» digit .
to ‘be signaled.
pulses. These pulses are in the form usua1ly;called.‘¿‘opent.
Outgoing call
Seizure-The first call to be described is one from
subscriber A to a subscriber in a distant terminal such
loop pulses.” That is,',.a~’dia1' at subscriber A’s telephone
station'` may' bey operated ‘..in ,-»a ; conventionalz-manner» re-.-
sponsive'toawhich appropriate springs vopen.»and .close-
esagera
5
6.
the talking loop across conductors T and R a suitable
number of times to transmit the proper digit pulses that
are representative of the called subscriber’s number.
Since the loop across conductors T and R is broken
Contacts 312 close toä
operate a slave release delay relay 320, the circuit being
from ground (-1-) through contacts 255 and 312 to (_)
battery via the winding of relay 320. Relay 320 operates
on each digit pulse to be transmitted by the dial, the
circuit for calling bridge relay 240 is likewise broken;
therefore this relay releases and reoperates to repeat each
and locks to master ground via contacts 326. This relay
is a slave to relay 310. Contacts 321 open to forestall
master ground conductor MG.
any possible connection of dial tone at this time. Con
tacts 323 open to prevent any possible operation of switch
The repeated pulse is transmitted each time that calling
relay 370 until subscriber A answers and the hybrid
bridge relay 24€) releases to open contacts 241. That is, 10 circuit H31 is properly terminated. This prevents the
digit pulse.
the holding circuit for send relay 390 includes contacts
241, 361 and 329. Each time that contacts 241 open,
send relay 390 releases to open contacts 391.
Signal
equipment S31 then transmits these signal pulses by any
circuit from singing or howling. Contacts 324 prepare
a path for switch relay 370 when the called subscriber
answers. Contacts 325 open to prevent any possible
operation of permanent time relay 360. Contacts 327
suitable means to the distant microwave terminal.
For 15 open to prevent untimely operation of digit relay 340.
example, dial trunk selector 114 may utilize the digits
Contacts 321a open to prevent any premature release
in the manner explained below in the section “Incoming
of minor switch M831. Contacts 323a close to operate
Call” under “Dial Trunk Selector 114.” Contacts 242
also open the circuit to relay 250 responsive to the release
of calling bridge relay 240. However, release delay relay
25@ does not fall due to its slow release characteristics.
Contacts 243 close to operate digit relay 340 over the
following circuit: ground (-1-), rest contacts 243 on call
primary delay relay 33t) over the circuit including con-`
tacts 32311, olf-normal contacts 300, and the lower wind
ing of primary delay relay 330, to (_) battery.
It
operates and prepares a locking path for itself by way of
contacts 331 and 322a. However, this path is not completed because contacts 382 are then open.
ing bridge relay 240, operated contacts 256 on release
Contacts 328 close to initiate operation of interrupter
delay relay 250, rest contacts 32'7 and 345 to (_) 25 relay 230. The circuit for this extends from (_) battery
battery through the winding of digit relay 340. The
primary reasons for operating this relay at this time is to
terminate the permanent time measurement so that relay
through the upper winding of relay 2311, contacts 234, 224
and 328 to ground (-1-).
Two speed interrupter relay.-lnterrupter relay 230
360 may not operate to break the connection and to
begins to operate, release and reoperate cyclically to inter
terminate dial tone. In greater detail, it may be recalled 30 rupt the supply of tone to provide busy tone to any
that permanent time relay 360 operates only after re
stations which may attempt to originate a call at this time.
sistor R31 has had time to heat over the circuit including
Relay 230 operates in the following manner. Originally,
contacts 363, 342, 325 and 254. Now, this circuit is
broken by digit relay 340 at contacts 342. Also, con
tacts 341 open to break the path for transmitting dial -‘
tone to the calling subscriber. Once operated, digit relay
3411 locks for the duration of the outgoing call over the
path from (_) battery through the winding of relay 340,
capacitor C21 is charged over the circuit including the
upper and lower windings of relay 230 in parallel, capaci
tor C21 and resistor R21. Completion of the above
traced circuit from ground (-1-) on contacts 328 through
the upper winding of relay 230 causes capacitor C21 to
discharge and »differentially energize relay 230 to prevent
its operation. After the discharging current through
capacitor C21 ends, relay 230 operates over its upper
winding from the ground (-1-) at contacts 328. This in
contacts 346, 225, and master ground conductor MG,
to ground (-1-) at contacts 257.
Conversation follows by way of the tip and ring con
ductors T and R shown near the top of the drawing by
turn opens contacts 234. Capacitor C21 is discharged at
means of heavily inked lines.
this time; therefore, a charging current begins to flow
Release-Either party may hang up ñrst at the termi
`from (_) battery through the upper and lower windings
nation of the call. It is assumed that subscriber A hangs
of relay 230 in series_this time the direction of current
up iirst to break the loop extending to calling bridge relay 45 flow is in a direction which is in series aiding so that
240. It releases. Contacts 242 open to restore release
relay 230 remains energized over a brief period of time.
delay relay 250. Contacts 241 open to release send relay
When the capacitor is fully charged, the charging current
390, thus releasing the channel. Contacts 257 open to
stops and relay 230 releases to close contacts 234 which
remove the ground (-1-) marking from master ground
starts the process all over again. Interrupter relay 230
conductor MG. Any relays then operated are released.
continues to operate and release periodically.
lf the called subscriber is the first to hang up, there
At this time it might be well to digress briefly to ex
is no eifect at the calling station, and the channel is held
plain the operation of interruptor relay 23() during ring
busy until the calling subscriber releases.
ing since this is a dual function relay and since the con
55 trast between the two functions is understood best if
Incoming call
Seìzure._-This call is one which is incoming to station
A from any other station in the microwave system.
explained together. As will be pointed out presently,
various digit pulses will be received and responsive thereto
a digit relay such as relay 2111 will operate at one termi
Referring to Fig. l, the calling station may be station C,
nal station depending upon the position of strapping B.
for example, and the call may originate as explained 60 When this digit relay operates, it closes contacts 216
below in the section “Outgoing Call” under “Dial Trunk
thereby shunting resistor R21 by connecting the right
Selector 114.” Signal equipment S41 associated there
hand plates of capacitors C21 to solid ground (-1-)
with is operated to transmit a seizure signal over the
instead of to resistive ground (-1-). This changes the
microwave channel to antenna 102. At this point, signal
speed at which interrupter relay 230 is operating, i.e.,
equipment S31 responds to cause the operation of receive
after operation of relay 216, the speed of interruptions
relay 380. The purpose for this relay is to receive in
are slower to provide ringing current, previously they
coming signals Iand to repeat them to control dial station
were fast to provide busy tone. Since the operated digit
selector 100. When receive relay 380 operates, contacts
relay is at one terminal station only, the other stations
381 close while contacts 382 open.
furnish busy tone to their subscribers with interruptions;
Responsive thereto, an obvious circuit is completed 70 at a higher rate of speed.
from ground (-1-) through operated contacts 381 to
The circuit is now in condition to receive the first digit
operate release delay relay 310. rl`his relay furnishes
pulse train. Therefore, nothing further happens until it
master ground to hold selector 100 and its associated
is received. The purpose of relay 330 is to mark the
relays until release of the circuit after the call is complete.
end of each incoming digit pulse train.
Contacts 313 close to apply this ground (-1-) marking to 75 First digit._The digit pulses which are received over .
2,894,074A
8`Í`
antennav 102 from the distant microwave terminal are con
ing path for primary delay relay 330; however, again, it
continues> to. hold‘ throughout pulsing due toits slow re
lease characteristics and- the circuit» through its upper
winding and contactsl 331'-, 322i:V and 382. The minor
operative to cause repeated release and" energization of
receive relay 380. Responsive to each digit pulse, relay tí: switchislstepped out a number of times depending upon
the number of‘ pulses in the second pulse train.
380'releases to open contacts 381 while closing contacts
nected through multiplex- and microwave equipmentv 101
to signal equipment~ S31ï.
These digit pulses» are then n
382. Release delay relay 310 is deenergized each time
Assuming that seven digit pulses areîreceived, wiper 302
that contacts 381 open; however, it does not release but'
is directed to the seventh terminal in the bottom level
which’is individual to ten or less stations including sub
continues tohold due-to its slow release characteristics.
A circuit is completed to cause minor switch-M831 to' lO scriber A. This time both digit relay 340 andy transfer
relay 350 are operated and locked to master ground as
takev one step each time that contacts 382 close responsivev
a result of the first digit; therefore, the circuit to digit
to a digit-pulse. The stepping circuit may be traced from
ground (-{-) through contacts 382, 322er, 331’ andv> the
winding of step magnet S to (_) battery‘and in pa'rallel4
therewith through the upper winding offrelay 330" to (_)
lbattery.y When magnet S- operates, it drives brushes`3`01
relay 2-10 is completed through contacts 354 instead of
and 302 into their associated bank‘ of contacts. Simul
contacts 226, 217, and `through the- winding of digit vrelay
taneously therewith, off-normal contacts 300~open while
contacts 303 close. Primary delay relay- 330» hasy its’
original` operating path brokenv at oit-normaly contacts
ground at contacts 218,' 225, andv conductor MG to
ground (-l-) on'conta‘cts- 313. Contacts 216 close to
355 as wasv they case after theV first digit was received.
Hence, a: circuit is'> now completed from’ ground (-1-)
through contacts 32311, 332, 354, brush 302", wiring B,
210 to (_) battery. t It’operates and locks to master
300; however, it does not release at this time since it is
change- the‘speed of interrupter relay 230 by shunting
further energized> by way of its upper winding and con
tacts 331, 322a and 382. As each digit pulse terminates,
receive relay 380 reoperates to close contacts 381 thereby
resistor R21. The purpose of relay 210 is to register the
-reenergizing release delay relay 310.
therewith, contacts 382 open to deenergizeV both primary
delay relay 330 and magnet S; however, relay'330 re
mains operated due to its slow release characteristics.
rIlhe minor switch is operated one step for each digit
station would have been operated. Since bothv digits in
the directory number ofsubscriber A `have been received`
the circuit is 'prepared to transmit ringing 'currentto signal
the called subscriber.
Ringing-_Ringing current is transmitted'from a' ring
pulse to be received. At the termination of-'the last pulse '
in the ñrst pulse; train, contacts 382 remain open for a
ing'generator (not shown) through the “generator” con
ductor, contacts 233, the upper Winding ‘of ring trip‘relay
period which is longer than the slow release' period ofv
primary delay relay 330; therefore, it releases to closeV its
220, contacts 215, conductor R, subscriber station A, con
ductor T, and contacts 213 to ground (-1-). Since inter
contacts’332 and open its contacts 331.
rupter relay 230 is` alternately operating and releasing
Simultaneously f
digit' “7.” If some digit other than “7” had- been re
ceived, a relay corresponding’to relay 210 at a different
The next function depends upon the particular step to 35 depending kupon the characteristics of capacitor C21, ring
ing current is interrupted repeatedly at contacts 233. lt
which the minor switch has been directed. For‘eXample,
might also be noted that operation of digitïrelay contacts
assuming that the ñrst pulse train comprised two digit
pulses, brush 301 is left standing on the second terminal
216 has shunted resistor R21 to change the> pulsing rate
of relay 230 from the busy tone speed to the ringing
to which the wiring A is connected. Since wiringA is
individual to ten or less stations including> the circuit 40 speed. During quiescent periods, (_) battery isa’pplied
at contacts 232. Ring back tone is connected from the
of station A-_assumed to have the directory number
“27”-a circuit is completed for operating digit >relay 340.
generator lead through contacts 233, th'e upper winding
of ring trip relay 220, contacts 215, capacitors C24 and
This circuit may be traced from (_) battery lthrough the
C25, ring conductor R, hybrid circuit an'd'bal'ancin‘g net
brush 301, contacts 355, 332 and 323a to ground (+). 45 work H31, modulator M31 and out over ‘antenna 102 to
the calling subscriber.
If the minor switch had been directed to some other ter
Anwen-Ringing continues until the called‘p’arty re'
minal, a ditîerent group of digitrelays similar to‘relay
sponds by removing his receiver therebyy completing a
340 would have been operated. Therefore, it is eseen’ that
the purpose of operating this relay at this time’is to iden
direct'current loop over a circuit which may be traced
tify the first digit in the called subscriber’s directory num- ' from (_) battery through contacts 232, the upper wind
windingof digit relay 340, rest contacts 345, wiring A,
ber. Contacts 346 close to lock digit relay 340' in an
operated condition de"endent upon the maintenance-of
master ground from contacts 313 through contacts 225
and 346. Contacts 343 close to release minor switch
MS31. The release circuit may be traced from (_)
battery through the winding of release magnet R, operated
off-normal contacts 303, operated contacts 343, and rest
contacts 351 to ground (-i-). Minor switch M531 returns
to -normal thereby opening oñ-normal contacts 303‘while
closing oiî-normal contacts 300. Transfer relay 350 now
operates over the circuit from (_) battery through con
tacts 352, 344, 300 and 32311 to ground (-l-). It loclzs
through contacts 353, 225 and 313. its purpose is to
prepare the circuit to register the second digit.l Primary
delay relay 330 reoperates over the circuit from (_)
battery through its lower winding, contacts 300 an‘d323a
to ground (-1-).
Second digit-_The circuit is vnow prepared tol receive
the second train of digit impulses. Again, receive relay
ing of ring trip relay 22m-contacts 215, conductor R,
subscriber substation A, conductor T, and contacts 213 to
ground (-{-). Ring trip vrelay 220 operates its preliminary
or “X” contacts 223'arid thereby energizes its lower wind
ing the circuit being from (_) »battery through the lower
winding of ring trip relay 220, contacts 223, and master
ground conductor MG, to master ground (-1-) applied
through operated contacts 313. With' this, ring trip relay
220 receives enough current to operate fully. Contacts
221 open to break still another point inthe dial tone
circuit. Contacts 222 close part’of a circuit for switch
relay 370 over the following circuit: (_) battery through
the winding of relay 370, contacts 222, 324 and`253 to
ground (+). (Operation of relay 250 will'be described
presently.) Contacts~224 open to stop the interrupted
operation'of relay 230. Contacts 225~open to release
digit relays 210 and 340l and transfer relay 350'. Con
tacts 226 open to prevent any possible' reoperation of
380 releases responsive to each impulse that is received
relay 210.y Digit relay 210 releases and opensïcontacts
over the microwave channel.
213 and 215. Contacts’212 and 214 close, thus’com
pleting a circuit forI energizing callingv bridgerelay 240.
This circuit may be traced from groundï (’-|-î)itbrough
As in the case of the ñ-rst
digit, a circuit is completed through contacts 382, 322a
and 331 to operate step magnet S and energize relay 330
in parallel therewith. Responsive to the iirst step yoir
normal, contacts 300 open to break-«the original energiz-l
the upper winding of calling bridge relay 240, contacts
212, tip conductor T, subscriber station A, ring >conductor
2,894,074?
R, contact 214 and the lower winding of calling bridge>
re'lay 240 to (_) battery.
When relay 240 operates, contacts 241 close; however,
they have no effect at this time since the operate circuit
for send relay 390 is held open by release delay relay 320
at contacts 329. This arrangement prevents inadvertent
and wiring Y is omitted, a first subscriber is called and"
instructed to wait for a conference call. The calling
party or operator disconnects and restores the dial sta~
tion selectors. Following this, the calling subscriber or
operator dials to signal the next subscriber to be in on
the conference call. In this manner any number of sub
scribers may be signaled for a simultaneous or conference
operation of send relay 390 when the circuit is in use on
an incoming call.
call.
Release delay relay 250 operates over an obvious circuit
It might be noted that switch relay 370 originally op
including contacts 242 to apply an alternate master ground 10 erated over the circuit from (_) battery through the
at contacts 257, and to complete the above noted circuit
winding of relay 370, contacts 222, 324 and 253. The
to switch relay 370 (i.e., ground (+), contacts 253, 323
called subscriber answers and relays 240 and 256“ operate.
and the winding of relay 370, to (_) battery). Con
Relay 320 is now locked operated over the path including
tacts 371 and 372 connect the demodulator to hybrid
circuit H31.
contacts 326 and 257 to ground (-|-). Switch relay 370
Conversation follows. At the termination of the con
versation, release is as described above in the section
entitled “Release”
If subscriber A is not at the called substation and if '
(_) battery extended through the winding of relay 320,
does not thereafter release until called subscriber A hangs
up. Hence, subscriber A remains in telephonie communi
cation with the microwave channel while the conference '
call is being set up.
the iirst digit to be dialed is not one marked in the banks
In the second case where listen-in service is not pro
of minor switch M831 by wiring A, a relay corresponding
vided, wiring Y is used and wiring X is omitted. When
to relay 340 does not operate in subscriber A’s dial sta
subscriber A removes his receiver and the channel is in
tion selector circuit. In this case, contacts 343 never
close, thus the minor switch does not return to normal
use, calling bridge relay 240 and release delay relay 25@
operate in the manner described above in the section re
after the ñrst digit. Rather, the minor switch remains 25 lating to the outgoing call. However, send relay 390
operated throughout the entire conversation. At the end
may not operate because contacts 329 are open; there
of conversation and when all relays are normal, the
fore, subscriber A cannot make a call. Busy tone is
minor switch is returned to normal because a circuit is
then closed from ground (-l-) through contacts 258, 321a
extended to inform him of this fact from the tone gen
erator TG21 over the tone conductor, wiring Y, contacts
and 303 to release magnet R and (_) battery. When 30 211, 221, 231, 322, capacity C31, contacts 212, subscriber
the switch returns to normal, olf-normal contacts 300
A’s telephone, contacts 214 and the lower winding of
close and 303 open thus leaving the switch ready for the
calling bridge relay 240 to (_) battery. Incidentally, it
next call.
On the other hand, assuming that a subscriber is called
(other than subscriber A) so that a wiring “A” is on the
minor switch bank contact that is reached responsive to
the first digit, minor switch M831 operates in a manner
might be noted against that relay 320 is operated as a
slave of relay 310 which in turn is operated by receive
relay 380 because the channel is busy; therefore, inter
rupter relay 230 is alternately operating and releasing at
a relatively high rate of speed due to the fact that con
described above in the section entitled “Incoming Call.”
tacts 328 are closed.
Digit relay 340 releases and the switch drops back to nor~
mal. When the switch is directed by the second digit, 40
Incoming call to dial trunk selector 114
it stops on a bank which is not marked by wiring “B.”
Hence, a relay corresponding to digit relay 210 never op
The next call to be described is one that is incoming
erates in this particular selector switch circuit. Again,
to dial trunk selector 114. For example, referring to
the minor switch remains in its extended position until
Fig. 1, this call could be from subscriber A to subscriber
the termination of the call at which time it releases over
C by way of channel 1 and its associated equipment in
the circuit including contacts 25S, 321a and 303.
cluding dial trunk selector 114.
Listen-in service and multiple signaling for microwave »
subscríbers
Two types of service may be provided.
Seízure._-Referring to Fig. 4, the presence of an in
coming call is signaled when receive relay 420 operates
In the ñrst 50 responsive to a suitable signal received by signal equip
case, a subscriber who is not a party to a conversation in ‘
ment S41 over antenna 112 from a calling station on
progress may be permitted to listen-in determine whether
there is conversation on the line. In the second case, the
subscriber is not permitted to listen-in on the conversation
but he receives busy tone indicating that the channel is 55
channel 1. Receive relay 420 operates and closes its
contacts 421. Responsive thereto, pulse relay 510 op
in use.
In the first case, wiring Y (upper left-hand corner of
Fig. 2) is omitted and wiring X (center of left-hand edge
erates over an obvious circuit. The purpose of this relay
is to receive and repeat signal and supervisory currents
from the distant oñice.
Responsive to the operation of pulse relay 510, con
tacts 511 close to prepare a circuit for transmitting ring
back tone when appropriate.
of Fig. 2) is used. In this case subscriber A can listen
Contacts 513 close to operate release delay relay 53€).
in on a conversation then in progress. That is, when 60
The primary purpose of this relay is to furnish master
subscriber A removes his receiver and relays 240 and 250
ground vfor holding the circuit operated when pulse relay
516 releases during digit pulsing. Contacts 532 close to
calls, a circuit is completed for energizing switch relay
mark channel 1 busy to outgoing calls from the cordless
370. This circuit extends from (_) battery through the
winding of relay 370, wiring X, contacts 324 and 253 65 P.B.X 116. This circuit may be traced from ground (_)
applied through contacts 552, 541, 532, conductor H and
to ground (-|-). It might be noted that relay 320 was
busy lamp L70() to (_) battery. Lamp L76@ lights as
operated responsive to the operation of receive relay 380
operate, as described above in the section on outgoing ‘
when the call was originally set up. When switch relay
370 operates, contacts 371 and 372 close thereby con-- -
an indication that channel 1 is in operation. Contacts
534 close to apply a ground (~|-) marking to master
necting the demodulator D31 to the hybrid circuit H31 70 ground conductor MG’. Since this ground marking is
so that subscriber A may listen to the conversation.
used to hold most relays in the trunk selector, it is called
As will be explained below in the section entitled “Con~
“master ground” hereinafter, and the conductor to which
ference Call,” this listen-in feature may be used to pro
it connects is labeled MG’. Contacts 533 close to op
vide for simultaneous service to more than one subscriber
erate release delay slave relay 52d. The circuit for op
on the microwave channel. That is, if wiring X is used 75 grating relay 520 extends from ground (-|-) through con~
2,894,074 ‘
11
12
register the tens group that includes the called line. Con
tacts 451 open to break still a further point in the dial
tone circuit. Contacts-452 close to release` the minor
switch. This circuit may be traced from ground (-{-) to
tacts 556 and 533 to (_) battery by way of the, winding
of relay 52€).
Release delay relay 520 operates.
Its contacts 521
open to forestall transmission of dial tone. Contacts 522
contacts 441, operated contacts 452, operated off-normal
contacts 402, the winding of release magnet R, to (_)
battery. Magnet R operates and the switch drops back
to normal thereby closing otî-normal contacts 401.
open to prevent operation of send relay 410 if the called
party is last to release. Contacts 523 close to lock relay
520. in an operated condition depending upon the main
tenance of master ground at contacts 534. Contacts 525
open one release circuit of the minor switch M541'. Con
Digit relay. 450. locks in an operated condition over con
tacts 526 close to prepare a holding circuit which -is com 10 tacts 454, rest contacts 567 and master ground conduc
pleted during pulsing for primary delay relay 460. Con
tor MG’ to ground (-1-) on contacts 534. Contacts 454
are arranged to make before contacts 455 break so that
tacts 527 close to start tone generator TGSI. This tone
generator is any suitable device designed to provide dial
digit relay 450 is held positively during its operation
tone. For example, it may be the same as tone generator
period.
TG21. Contacts 528 close to operate primary delay: re
lay 460. The circuit for this function extends from
A circuit is completed through resting off-normal con
tacts 401 for operating transfer relay 440, the circuit be
(_) battery through the lower winding of primary delay
ingf from (_)1 battery through the windingl of relay-’440,
relay 460, resting off-normal contacts 401, operated con-..
tacts 528, to master ground conductor MG' and ground
rest contacts 442, operated digit relay contacts- 453, rest
ing off-.normal contacts 401, operated contacts 528 and
20 534 to ground (+). A purpose of the transfer relay is
(-}-) applied through operated contacts 534.
Primary delay relay 460 operates. The purpose of
to transfer the minork switch control circuit to a units
this relay is to mark the end of each digit pulse train
digit relay;
as it is recevied. Contacts 461 close but have no. effect
at this time. Contacts 462 close further to prepare part
operates `in parallel with transfer relay 440. This circuit
may» be traced fromk (_) battery over the lower winding
Incidentally, primary delay relay 460» re
of the circuit over which primary delay relay 460- is held 25 of relay 460, resting off-normal contacts 401', operated
throughout pulsing. Contacts 463 open to prevent a
contacts 528 and 534 to ground (-l-). Transfer relay
ground (-1-) marking from being extended over the upper
440 opens contacts 441 thereby breaking the circuit over
bank of minor switch M841 until the end of the corn
which the minor switch was released. Contacts 443 close
pleted digit pulse train. The circuit is nowy ready to re
ceive the digit pulses; therefore, nothing further happens
to lock transfer relay 440 to master ground by way of
30 contacts 5.67 and 534. Again, contacts 443 are arranged
at this time.
to make before contacts 442 break so that transfer relay-
Dial pulses-_When the calling- subscriber transmits-the
first digit pulse train, signal equipment S41 responds in
44.0. is. held positively throughout armature travel time.
Contacts 444 close and 445 open thereby transferring
digit registering control from the upper to the lower bank
any suitable manner to cause receive relay 420 to release
and reoperate responsive to each. digit pulse.l
21 follow to open and close the circuit to Vpulse relay
510 thereby repeating each digit pulse. Each time, that
pulse relay 510 releases, contacts 512 close to'transmita
digit pulse into minor switch MS41. The pulsing path
may be traced from ground (-}-) applied through con
of minor switch M841.
Thev circuit is now prepared to receive the second digit
pulse> train. Receive relay 420 is released to open con
tacts 421 responsive to each digit pulse in the second digit
pulse train. Responsive thereto, pulse relay 510 releases
and reoperates repeatedly. On each release of the pulse
tacts 512 to operate contacts 526, 462, rest contacts 569
relay, a-circuit is completed from contacts 512 over con
and through the winding of step magnet S to (_) bat
tery. A circuit may also be traced from contacts-#462
tacts 526. and 462 to. primary delay relay 460 and in
parallel therewith through contacts‘569 to step magnet S.
Responsive. to each digit pulse, stepy magnet S drives
through the upper winding of relay 460, therebyv energiz
ing it repeatedly throughout pulsing.
wipers 403 and 404 one step further-'into the bank of con
When step magnet S operates to take its tirst step there
by driving wipers 403 and 404 into its associated banks,
tacts. Assuming that seven digit pulses are received,
wiper 404Y is left on the seventh» terminal to whichl strap
ott-normal contacts 401 open and 402 close. When con
D2 is connected. A circuit is completed for operating
digit relay 560 as a registration of the second digit and
tacts 401 open, the original energizing path for primary
_asanV indication that the particular circuit shown is to be
seized. If the minor switch had been directed to another
bank contact in the lower level, a corresponding digit
relay in a different selector would operate at this time as
delay relay 460 is broken so that this relay must herein~
after depend upon the energizing current that it receives
through its upper winding; or, stated another way, during
the interval between each digit pulse, primary delay relay»
460 is deenergized but it continues to hold due to its slow
release characteristics. Also duringy the interpulse time,
release delay relay 530 is deenergized when» contactsy 513
open; however, it too remains operated over this-period
an indication that that circuit was called.
55
Incidentally, trunk selector 114 may be associated with
either a manual exchange such as cordless P.B.X 116 or
a dial exchange such as 108, for. example. Any selector
such aszselector 114 may serve either a dial exchange or
-a cord1ess~„P.B.X' but a selector of this type would never
Step magnet S continues to be operated by each- Ldigit
pulse. It drives wipers 403 and 404 further into the 60 _serve both. Assuming that the trunk selector 114is ar
due to its slow release characteristics.
rangedI toA connect with cordless P.B.X 116, contacts 612
are providedin an adapter circuit'and wiring Z is omitted.
On the other hand, if this selector is arrangedlto seize:
standing on the third terminal to which strap D1 is con
dial P.B;X.108, contacts 612` are. omitted and wiringZ
nected. Since no further pulses are received after the ~
third pulse, in the case assumed, primary delay relay 65 is used. In either event, digit relay 560 is operated over.
a circuit which may betraced from (_) battery through'v
460 restores. In doing so, it closes contacts 463. A cir
the winding of relay 560, contacts 612 (or wiring Z, as the
cuit is now completed for operating a particular digit
banks at the rate of one stepper digit pulse. Assuming
that three digit pulses are received, wiper 403 is left
relay depending upon the position to which the minor
case may be), strap D2, wiper 404, operated- contacts
switch has been stepped. In thisV case, it is assumedthaty
there were three digit pulses; therefore, a circuit is com-->
444, rest contacts 463, and operated contacts 528y and 534
pleted from (_) battery through the winding of relay
to master: ground (-f-). If this were a call. to a dial ex-A
change, contacts1561a would now close to seize a line
450, rest contacts 455, strap D1, shorting brush.403‘, con
tacts 445, 463, 528, and master ground conductor MG'
to ground (-{-) at operated contacts 534.
Digit relay 450 operates. The purpose of'thisrelay iszto, 75:
circuit ofzthe dial exchange. However, if it is assumed
that digit relay. 560 serves a cordless P.B.X, contacts’
Stile-are not used. In` this case, talking conductorsTlf
and: R1» are connected through contacts 562 and 56.4,.
2,894,074
13'
'while calling bridge relay 570 is disconnected from the
talking conductors at contacts 561 and 563. Digit relay
56@ locks to master ground by way of contacts 612, 566
and 534. Contacts 567 open to release digit relay 450
and transfer relay 440 since they are no longer necessary.
Contacts 568 close; however', they have no effect at this
time.
PBX-Contacts 565 close to light an incoming lamp
at the operator’s position thereby indicating to her that
with the local talking conductors of the called line.
Assuming that the subscriber at station C has been
called, operator OP800 moves key K920 so that contacts
a call is to be answered. The circuit for this operation
may be traced from ground (-|-) on contacts 565, rest
K921-K925 are closed. A circuit is now completed
from ground (-|-) through contacts K921, K706, and con- ~
contacts 623, incoming lamp conductor INC, through the
filament of lamp L7 01, contacts K713 and the winding of
relay 65@ to (_) battery. Alarm relay 650 operates in
series with incoming lamp L701. Contacts 651 close to
ductor LK to operate relay 610 in adapter 115. Con
tacts 612 open to release digit relay 560. Contacts 611
open to break still another point in the ring back tone
circuit. Ringing key 800:1 is operated to the left and sub
complete a circuit fromy ground (-1-) on busy key K800
through contacts K805, 651, a retard coil RC61, contacts
scriber C is rung, the ringing current being traced from »
the generator conductor over contacts K801, conductor
661, and the winding of buzzer 660 to (_) battery. The
buzzer operates and opens contacts 661 thereby breaking
R3, the subscriber C substation, conductor T3, operatedv
its own circuit and causing it to buzz. This buzzer con- u
key K800i: to normal after she has rung the called sub
scriber. When called subscriber C answers, the talking
this portion of the call from battery B81 (lower `center
of Fig. 8) through the winding of an unnumbered relay,
transmitter T1 of operator’s telephone set 117 and hook
switch contacts H881 to ground (-}-) G81. Upon learn
ing the destination of the call, the operator moves a suit
able key for connecting the incoming talking conductors
contact key F1804 to ground (-1-). The operator returns '
tinues to sound in the well known manner until the
operator at the cordless P.B.X answers the call.
path is completed over- conductors T3 and R3, contacts
K803 and K802, through similar contacts in links 1 and
Ring back tone is transmitted to the calling subscriber
to inform him that a signal has been transmitted to the
2, operated contacts K922 and K925, operated contacts
The path for ring back tone may be traced 25 K704 and K703, rest contacts Kótll. and 1(602, conductors
from the generator lead, Fig. 6, through contacts 621,
T1 and R1, hybrid circuit H41, modulator M41 and
611, operated contacts 562, conductor T1, hybrid circuit
demodulator D41, microwave equipment MW41 and over
H41, modulator M41 and microwave equipment MW41
antenna 112 to channel 1.
to antenna 112.
Means is provided in dial trunk selector 114 to furnish
The operator notes the sound of the buzzer and the
talking battery to the called subscriber served by the
incoming lamp L701 signal and proceeds to select any
P.B.X. That is, calling bridge relay 570 operates, its
idle link to complete the call, for example, link 3 which
purpose being to extend talking battery over part of the ~
includes key K700. The purpose of this key is to extend
above traced talking circuit to subscriber C. The operate
the conversation conductors to a point where they may
circuit for relay 570 and the talking battery circuit are connect with the line of the called subscriber. There
extended from (_) battery through the upper winding of
operator.
fore, to answer the call she moves this key so that the
contacts K701-K706 are operated. Contacts K702
calling bridge relay 570, contacts 561 on relay 560, con
complete an obvious circuit for operating cut-off relay
nection extends through the lower winding of calling
‘bridge relay 570, released contacts 563 and conductor
’730.
ductor T1 to subscriber C, and the ground (-{-) con
Relay '730 operates and opens contacts 731 and
'732 thereby cutting off the battery normally supplied
through the winding of calling bridge relay 740. This
battery is used on calls which are local to the P.B.X.
The operator also throws her talk key K910 which is
associated with link 3. The purpose of this key is to
connect the operator to talk to the calling subscriber
and to retire the calling signals including lamp INC and
buzzer 660. This closes contacts K911-_K913.
A cir
cuit may be traced from ground (-i-)through contacts
40
R1 to subscriber C. Contacts 572 close thereby operating
release delay relay 550 over an ob-Vious circuit. Contacts
552 open thus extinguishing the “busy and hold” lamp
L7il0 indicating to the operator that the called station
has answered. Formerly, this circuit extended from (_)
battery through the ßlament of lamp L700, conductor
H, contacts 532, 541 and 552 to ground (--l--).
The operator has completed her service therefore she
restores talk key K910 to its normal position (the op
K911i, K7tl5, conductor TK, to (_) battery through the
erator may restore the talk key immediately after ring
windings of relays 630 and 620 in parallel.
50 ing the local station), thus breaking the talking connec
Relays 620 and 630 operate. Contacts 623 open to
tion to her headset. Contacts K911 open thereby releas
break a circuit formerly extending through contacts 565,
ing relay 630. It might be recalled that relay 630 origi
623, conductor INC, the ñlament of lamp L701, contacts
nally operated over the circuit which may be traced from
K713i», and the winding of relay 650 to (_) battery; there
(_) battery through the windings of relay 630, conductor
fore, lamp B701 and buzzer 660 are retired. Contacts
TK, contacts K705 and K911 to ground (-f-). Relay 630
621 open to terminate ring-back tone. Contacts 631 and
632 have no function at this time.
Contacts 633 apply
ground to conductor HS thereby operating switch relay
releases; however, relay 620 which originally operated
in parallel to relay 630, continues holding and does not
release since it has locking contacts 622 which connect
Responsive to the operation of relay 430, contacts 431 60 with master ground conductor MG’ and ground (-1-) on
operated contacts 534. Contacts 633 open because they
and 432 close to connect the demodulator into'the talking
are no longer necessary to hold switch relay 430 operated
circuit. The purpose of this relay and these contacts is
because release delay relay 550 has closed contacts 553.
to keep the circuit from singing or howling until the line
Conversation follows.
side of hybrid circuit H41 is properly terminated, i.e., the
Release.-At
the termination of the call the particular
talking conductors have been extended to an operator’s
sequence of circuit functions depend upon which sub
or subscriber’s telephone.
scriber is the iirst to hang up. Assuming ñrst that the
The operator is now connected with the calling sub
called
subscriber restores his receiver before the calling
scriber and may inquire to determine the destination of
subscriber, calling bridge relay 570 releases when the
the call. The talking circuit may be traced from opera
called subscriber hangs up to break the talking loop
tor position 0F80() through tip and ring conductors T2 70 which
extended from (_) battery through the upper
and R2, contacts K913 and K912, contacts K704 and
winding of calling bridge relay 570, rest contacts 561,
R763, contacts K601 and K602, conductors T1 and R1
conductor T1, contacts K601, K704, K925, contacts in
to hybrid circuit H41, modulator M41, microwave equip
links 2 and 1, rest contacts K803, tip conductor T3, '
ment MW41 and antenna 112 to channel 1 and the call
calledk subscriber station C, ring conductor R3, normal
ing subscriber. The talking battery may be traced during
contacts K802, contacts in links 1 and 2, contacts K922,' '
43@ over an obvious circuit.
2,894,074 '
15`
K703, K602, ring conductor R1, rest contacts 563 to
ground (+)' through the lower winding of calling bridge
relay 570.
16."
sounded._ The circuit for this includes contacts 661,
651, K805 and bus'y key K800 to ground (-1-).
Operator OP800 notices the lit condition of lamp L901
and theaudible signal òf buzzer 660 and she responds by
When calling bridge relay 570 releases, it opens con
tacts 572, thereby causing the restoration of release delay Ct operating a keyf in any idle. link. For example, she may
operate key K920 if link 3 is then idle. She also operates
relay 550. Contacts 553 open thereby releasing switch
her talk key K910 so that she may inquire of subscriber C
relay 430. Contacts 552 close to light busy and hold
to determine the destination of the call.
lamp L700 via contacts 541, 532, conductor-H, and lamp
Calling bridge relay 740 operates responsive to opera
L700 to (_) battery as an indication that the called
tion of key K920, the circuit being from ground (-|-)
subscriber has hung up but that the selector is still busy
through contacts 732, operated contacts K925, rest con
because the calling subscriber has not yet hung up. It
tactsin links-2 and 1, rest contacts K803, tip conductor
might be noted that busy and hold lamp L700 is an indi
T3,~_subscriber station C, ring conductor R3, key contacts
cation ofV an unattended and incomplete call rather than a
K802, resting key contacts in links 1 and 2, operated con
mere busy lamp in the normal meaning of they word.
Nohing further happens until the calling subscriber
tacts K922, contacts 731 and the winding of calling bridge
hangs up. At that time signal equipment S41 is operated
relay 740 to (_) battery. Theoperator converses with
by any suitable means (not shown) to release receive
the calling subscriber to determine the destination of the
L703 as an indication that the operator should return the
If the call werel to another local subscriber, operator
OP800 would move a key (not shown) corresponding to
key K920'.
On the other hand, it is assumed that the call is for a
subscriber who must be reached by way of antenna 112
and channel 1. Therefore, operator OP800 moves key
K700 to interconnect the local subscriber and the outgoing
trunk circuit. Adapter relays 620 and 630 operate to pre
call. The talking path includes conductors T2 and R2,
relay'420'. Responsive thereto, contacts 421 open thus
operated contacts K912, K913,_K925 and K922, and con
breaking a holding circuit for pulse relay 510 which
releases. When relay 510 releases, contacts 513 open 20 ductors T3r and R3 to subscriber C. Upon learning the
destination of- the call, operator OP800 actuates suitable
thereby restoring release delay relay 530. Responsive
keys.
thereto, contacts 531 close to light supervisory lamp
keys in the cordless P.B.X to normal. The circuit for
lighting this larnp extends from ground (-}-) through ‘
normal contacts 552, 541, 531, conductor SR, operated
contacts K701, 733, 741, the ñlament of lamp L703,
alarm relay 650 to (_) battery. Relay 650 closes con
tacts 651 thereby operating buzzer 660 over a circuit
which maybe traced from (_) battery through relay
660, contacts 661, 651, K805 and busy key K800 to
ground (+). Lamp L703 and buzzer 660 cooperate to
indicate to operator OP800 that the call should be taken
down. Relay 530 also opens contacts 534 thereby re
moving master ground so that any remaining relays that
are operated are restored at this time. One of these
pare dial trunk circuit selector 114. The circuit for op
erating these relays extend from (_) battery through the
lwindings of relays 620 and 630 in parallel, conductor TK,
operated contacts K705 and K911- to ground (-4-). Relay
620 holds incoming conductor INC open at contacts 623,
thereby preventing any false incoming signals at lamp 701.
Contacts K702 operate cut-off relay 730 thereby open
ing contacts 731r and 732 to disconnect calling bridge relay
740. This is «because talking battery will be furnished
relay 520 restores, contacts 525 close to release minor
switch M841. This circuit includes the contacts 559, 40 from this time on Aby way of the windings of calling bridge
relay 570. Contacts 733 close to give supervision on re
525 and operated off-normal contacts 402. Release
lease.
magnet R operates causing minor switch M841 to drop
Calling bridge relay 570 operates to `furnish talking
back thus opening oil-normal contacts 402» while closing
battery
to subscriber C and to receive and repeat digit
contacts 401. With the restoration of release delay relay
pulses; The circuit for this relay extends from (_) bat
530 (and consequently the breaking of master ground
tery through the winding of relay 570, contacts 561, con
(-{-) connection at contacts 534), the dial trunk selector
ductor T1, contacts K601, operated contacts K704, R925,
circuit> 114 is returned to normal and ready for the
resting key contacts in links 2 and 1, contacts KS03, tip
next call.
Y
conductor T3, the calling subscriber station C, ring con
Whenv operator OP800 observes the lit conditionY oi
lamp L703~ together with the'sounding of buzzer 660 she 50 ductor R3, contacts K802, resting key contacts in links
1 and 2, operated contacts`K922, K703, K602, ring con
restores keys K700 and K920. Relay 730 releases when'
ductor R1, resting contacts‘563 and the lower winding of
keyf contact K702 is open and adapter relay 610 restores
calling bridge relay 570 to ground (+).
when’key contacts K706 and> K921 release.
Calling bridge relay'570 operates and closes contacts
La UI 572 thereby operating release delay relay 550. The pur
Outgoing call from P.B.X
relays is release delay relay 520 which had been locked
Over'the circuit including contacts 523 and 534. When
pose of this relay isl to 4furnish master ground and there
The next call to be described is one which originates in
by hold'` the circuit operated throughout digit pulsing.
the cordless> P.B.X 116. For the purpose of explaining
Send relay 410 operates over a circuit from (_) battery
this type call, it is assumed that subscriber C is calling
through the winding of relay 410, contacts S71 and 522 to
another subscriber to whom access is had by way of
channel 1.
ground ('+). This relay closes contacts 411 thus caus
ing signal equipment S41 to transmit a seizure signal
to all microwave stations on channel 1.
Seizure-_To place this call, subscriber C removes his
receiver from its hookswitch. Responsive thereto,`bridg,e
relay 910> operates. The circuit for this operation may
be traced from ground (+) through its upper winding,
key contacts in link 4, rest contacts K924, contacts in»
linksk 2. and 1, resting contact K803, tip conductor T3,
subscriber subset C, ring conductor R3, key contacts
K802, contacts in links 1 and 2, rest contacts K923, key
contacts ink link 4, to (_) battery through thev lower
winding-,of relay 910 which operates. Responsive there
to,.a circuit‘is Lcompleted from ground (-{-) through op
erated contacts 911, lamp L901, resting key contacts
K956,’and through the winding of alarm relay 650 to (_)
battery; Contacts~ 651-close causingv buzzer 660 to be
Release delay* relay 550 operates. Responsive there
to,.contacts 5,58 close to apply master ground to conduc
tor MG’. This ground is called “master ground” because
it holds most of the relays in dial trunk selector 114 in
their operated condition. Hence, when this ground mark
ing is removed; substantially all relays release. For ex
ample, one circuit may be traced from ground (1+)
through operated contacts 558, master ground conductor
MG' andtoperated’contacts 622 and through the lower
windingV of relay 620 to (_) battery. This-relay is now
locke'cll‘operated-independently of the continued applica
tionof ground atcontacts K911. Contacts 557 close to
prepare acircuit forl digit relay 450. Contacts 554 close
2,894,074
18
'to extend a ground marking to the start conductor of tone
.generator TG51. This generator pro-vides dial tone. Con
Figs. 7 and 9, for example. Link 5 is especially arranged
tacts 553 close to operate switch relay 430 over an obvious
` for conference call service since it is arranged to use the
conference equipment, such as link 5 which is shown in
circuit. The purpose of this relay is to close contacts 431
line lamps for supervision of each line on a conference
and 432 thereby operatively connecting demodulator D41
to the microwave equipment MW41 since hybrid circuit
H41 will not sing when it is thus properly terminated.
and provides individual battery feed relays and has a
negative impedance that is adapted to Icompensate for
loss of audio signal according to the number of telephones
in the conference circuit.
Contacts 551 close to extend dial tone to the calling
operator. The circuit for dial tone extends Afrom tone gen
To set up the conference call the operator moves talk
erator TG51 over the tone conductor, contacts 551, 521, 10 key K950 and corresponding keys in the case of each
451, tip conductor T1, contacts K603i, K704, K913, tip
subscriber station to be included in the conference cir
conductor T2, to the operator’s headset, and back over the
cuit. It should be understood that the dotted lines be
circuit including ring conductor R2, contacts K912, K703,
tween Figs. 9 and 7 indicate that additional facilities may
K602, ring conductor R1, contacts 563 to ground (-f-)
be provided to accommodate over local and trunk lines,
through the lower winding of calling bridge relay 570.
Dialing-The circuit is now prepared to receive digit
pulses and nothing further happens until operator OP800
moves dial D301. In preparation for dialing, operator
15 part of these facilities being keys corresponding to talk
key K950. If the subscriber being called for the con
ference is in the oñîce served by the cordless P.B.X, the
next step is to operate intermittently a ring key corre
OP800 moves key K620 thereby opening the talking cir
sponding to key K800 associated with that subscriber
cuit at contacts K601 and K602 while closing a dial cir- 20 line. As each subscriber answers, a line lamp is lit dimly
cuit at contacts K603 and K604. Following this, the
to give oil-hook supervision.
operator moves dial D801. This dial is arranged to break
In greater detail, the conference call is set up in the
the talking loop which now extends from conductor T1
following manner. The operator receives the call in the
-over key contact K603, a dial conductor, `dial D801 and
manner explained above and determines that she must
back over another dial conductor, key contacts K604, 25 use link 5 to complete a conference call. First, she op
ring conductor R1 and contacts 563 to ground (1+)
through the lower winding of calling bridge relay 570.
Each time that dial D801 opens this loop, calling bridge
`»relay 570 releases to transmit a digit pulse by .opening
erates conference key K940. Then, assuming that local
line subscriber C is to be included in the conference,
she actuates key K950 and ringing key K800a. Con
tacts K804 and K801 close thereby connecting a ring
ycontacts 571. It might be recalled that ,send relay 410 30 ing generator to conductors R3 and T3, thus signaling a
:originally operated when calling bridge relay 570 operated,
athe circuit being from _(-) battery, through the winding
iof‘send relay 41.0, contacts 571 and 522 to ground .(\-|-).
Therefore, each time that call-ing bridge relay 570 opens
local subscriber C.
When local subscriber C `answers
and ringing key K800a is restored to normal, a circuit
is completed for operating bridge relay 910. This cir
cuit may be traced from ground (+) through the upper
‘contacts 571, send relay 410 is caused to release and cor 35 winding of relay 910, closed contacts on a talk key in link
respondingly to open contacts 411. This in turn causes
4, contacts K924, similar resting contacts on a talk key
.signal equipment S41 to repeat the digit pulse train to a
in link 2 and a talk key in link 1, normal key contacts
‘distant station by way of antenna 112 and channel 1.
K803, conductor T3, the telephone set at the station
Each time that calling bridge relay 570 restores responsive
serving subscriber C, ring yconductor R3, closed key con
to the receipt of a digit pulse, contacts 572 are opened to 40 tacts K802, normal contacts on a talk key in link 1 and
deenergize release delay relay 550. However, it does not
a talk key in link 2, normal contacts K923, similar normal
release due to its slow release characteristics. Also re
contacts in link 4, and through the lower winding of
sponsive to the first release of calling bridge relay 570,
bridge relay 910 to (~) battery. The purpose of this
contacts 573 close to energize digit relay 450. This cir
relay is to furnish talking battery, to control supervisory
cuit may be traced from (_) battery through the winding 45 lamp L901, to control the impedance in the talking cir~
of digit relay `450, rest contacts 455, 524, operated con
cuit and to switch the talking circuit through to the am
tacts 557 and restored contacts 573 to ground (1+).
plifier of Fig. 10.
Digit relay 450 is operated responsive to the receipt of
Bridge relay 910 operates and closes contacts 911. A
the first digit pulse. It locks by Way of its contacts 454
lcircuit is now completed for causing line lamp L901 to
to master ground by way of contacts 567 and 558. The 50 glow dimly as an indication that the called subscriber
reason -for operating the digit relay at this time is to open
is off-hook. The circuit for this is completed from ground
contacts 451 thereby terminating the transmission of dial
(-{-), through contacts 911, line lamp L901 and key con
tone to the calling operator.
_tacts K957 to (-~) battery by way of resistor R91. This
After all digit pulses are sent the circuit remains in the
lamp will continue to glow dimly until called subscriber
condition described until the called subscriber answers. 55 'C returns his receiver to its hookswitch to restore bridge
When operator OP observes the answer of the called
relay 910. Contacts 912 and `913 close to connect the
subscriber, she responds «by returning talk key K910 to
talking circuit from subscriber C to the conference arn
normal, thus releasing relay 630. Relay 620 does not re
pliñer. This talking circuit may be traced from subscriber
lease at this time since it has locked at its contact 622
station C over the heavily inked lines, through key K800a,
to master ground conductor MG’. The circuit continues 60 unnumbered talk keys in link 1 and link 2, a similar talk
in the condition described until the conversation terminates
>key in link 4, key K950, a pair of capacitors designated
at >which time release is as described above.
C91 and C92, operated contacts K952 yand K955, op
erated
relay contacts 912 and 913, operated key contacts
Conference call
K941 and K942, thereby completing the talking circuit
The next call to be described is a conference call. Re
65 into the conference amplifier.
ferring to Fig. l, it is assumed that various of the sub
scribers, such as A, B, C, etc., Wish to hold a simultane
The conference calls may also include subscribers who
are given service via the microwave channel. lf this is
ous or conference call.
the case, the operator moves talk key K710 or a similar
In this event, the operator at
cordless P.B.X 116 (Figs. 6-9) is called in any suitable
key that is individual to the channel which gives service
manner by the person placing the call. For example, the 70 to the particular microwave channel subscriber who is
call may be placed in the manner described above in
to be included in the conference call. Following this,
the section entitled “P.B.X.” When the P.B.X operator
the operator dials the called party’s directory number.
answers the call and converses with the calling subscriber,
There is no answer supervision when the subscriber
she is informed of the fact that there is need for a con
sen-ved by the microwave channel answers. Hence, the
ference call. Responsive thereto, she may use special 75 dim line lamp shows only that the channel is in use on a