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Sept. 24, 1946.
2,408,085
L. A. MEACHAM
COMMUNICATION SYSTEM
Filed July 23, 1943
v2TR0uR,
Na.
B)’
L
WAWMWm5M
ATTORNEY
Patented Sept. 24, 1946‘
*
2,408,085
UNITED. STATES PATENT OFFICE ~
Bell Telephone Laboratories, Incorporated, New
York,
Y., a corporation of New York
. Application July 23,1943, Serial No. 495,867
’
10 Claims,
(01. 179-15)
1
2
This invention relates to telephone systems
and particularly to intercommunicating systems
The conductors may extendibetweenr all suici-v
scribers’ stations‘in tandem, or be extended to the.
in which a plurality of carrier channels are pro-,
vided in a common transmission medium extend
various stations separately fromone or more‘ '
ing to all of the telephone stations in the system.
Objects of the invention are the improvement
of intercommunicating‘systems comprising a plu
omy and ?exibility. The direct current power
rality of carried channels in a common transmis
branch points, thereby to secure optimum econ-7
for the subscribers’ stations is, supplied, over the
aforementioned conductors, from a common bat
tery 5 which may be located at one of the sta
sion medium extending to all of thetelephone
tions or at any intermediate point. The common‘
stations and particularly in the provision of. a 10 medium affords a plurality of channels, each of a
system in which privacy is assured and in which
di?erent frequency; and each station in the ex
change or intercommunicating system is individ
a busy signal device is operated at a calling sta
tion if the called station is already connected in ‘ ,ually assigned two channels, one for receiving
and the, other for transmit-ting speechrand sig-v
communication with a third station.
J
The invention is an improved intercom-muni
nals on calls initiated at any other of the sta
cating system in which each of the telephone sta
tions. When a station is i'dleand also when it is ,
answering va call, it is tuned'to the frequencies of’v
tions is assigned a different, pair of carrier chan-,
nels in a common transmission medium extend.
these two assigned channels.‘ ' Whenasubscriber
ing to all of the stations, one of this pair of chan
calls another station, the calling subscriber‘ tunes
nels being used as a receiving channel, and the 20 the transmittingandv receiving circuits of the
other as a transmitting channel on calls incom—/
calling station to the frequencies of the channelsv
assigned individually to the called station, so that
ing from any other station, and in which each‘ of
the stations is arranged to select the , ‘pair of
the called stationis ready for conversation upon‘
channels assigned to any other station with which
removal of the receiver or handset‘ thereat from
communication is desired, According to, a fea
its normal position. To afford privacy, each sta
ture of the invention, means are provided for giV-' _ tion is arranged so that it is necessary for the
ing a busy signal to a calling station whenever
balling subscriber to test thecommon transmis
sion medium for the presence of a carrier of the
‘the station with which communication is desired,’
frequency of the individual transmitting channel
is busy, both when~ the last-mentioned station is
busy in communication with a calling station and 30 of the» station with which'conversation is desired,
before originating the ‘call. If carrier current of
' when the last-mentioned station is busy in com
munication with a called station.~ According to
this particular frequency is already present, a
busy signal is given to the calling,’ subscriber and
another feature of the invention, meansare pro
vided at each station for disabling a calling sta
the calling subscriber's station is rendered inop-=
tion when attempting to establish communica 35 erative Ito establishv a conversational connection
tion with another station which is then in com
with the busy station.
' '
' v
1;
munication with a third station.
The station A comprises a telephone handset
Other features will be apparent from the fol;
which is normally positioned in a supporting eralowing description of the system disclosed in the
dle, station keys, one for each of the other sta-'
drawing, which system constitutes one embodi
tions, an oscillator-modulator tube 80 for gener
ment of the invention. The invention is not lim
ating and modulating the carriers which are used,'
ited, however, to the system and detailed ar
to, transmit speech from station A to the other
rangements shown in the drawing but is-gener
stations, and an amplifier tube 85 coupling the
ally applicable to carrier intercommunicating
output circuit of tube 80 to the conductors I and 2;‘
45 The oscillator-modulator tube 80 is‘controlled by‘
Referring to the drawing, which consistsof a
the transmitter l1 and by two tuned circuits, one
of which comprises coil ‘II and condenser 13 and
single ?gure, the common transmission medium ‘
is tuned by the operation of any one of the sta
CM interconnects a, plurality of stations including
tion keys to generate a carrier of ‘the frequency
stationsA, B and X.‘ The station A is shown
in detail and each ‘of the'other stations is simi 50 of the receiving channel individually‘ assigned
to the corresponding station for transmitting:
lar thereto. The transmission medium CM may.
be any pair of conductors l and 2, ‘for instance a, _ speech from station A to the called station. The
other of these tuned circuits comprises coil 12 and’
twisted pair or a shielded pair or a coaxial cable,
systems;
,
'
'
.
which ‘is ‘multiplied toall subscribers .oi-a private
condenser 14 and is tuned to generate a carrier '
branch exchange or ‘ intercommunicating "system.. 55
of the frequency of the transmitting channel in-I
2,408,085
3
4
dividually assigned to station A and used to trans
mit speech to any other station when station A
is the called station. The tube 80 is also used
to generate a carrier of the transmitting fre
quency individually assigned to station A, when
of the cradle, the cradle supporting element it
effects closure of contacts l9 and the spring 21
rotates the actuating element 20 thereby to move
the locking plate 24 to its extreme right position;
in which position, operation of any station key
station A is busy as a, calling station, thereby to
is impossible due to the engagement of its locking
give a busy signal at any other station at which
the station A key is actuated to initiate a call to
Any key, which is depressed at the timev the hand
collar with the top surface of thelocking plate.
set is removed from the cradle, is locked in its
station A. Thermistor elements 15 and 16 con
stitute amplitude limiters in the oscillator circuit. 10 operated position, by the engagement of its look
ing collar with the lower surface of plate 22, until
Reference may be had to my Patent No. 2,303,485,
the handset is replaced. This key locking mech
granted December 1, 1942, for a detailed descrip
anism illustrates the desired control, which con—
tion of similar oscillator circuits for generating
' trol may be e?ected by any suitable mechanism.
a plurality of frequencies.
.Assume now that station A is idle, with the
The station A further comprises a transformer‘. '
handset in the cradle and all station keys nor
I0 and detector-ampli?er tube £5 for receiving
mal. Under this condition, the detector 55 is
speech modulated carrier currents incoming from
tuned. to the frequency of the receiving channel
any other station with which station A is in com
which is individual to station A. At this time the
munication, the receiver l6 being connected in
the output circuit of tube E5. The condenser I4 20 oscillator-modulator 8G .is tuned to generate a
carrier of the frequency of the transmitting chan
and primary winding of transformer it and the
nel which is individual to station A, the tuned
secondary winding of transformer It and con
circuit comprising‘ coil‘ 1 i' and condenser 13 being
denser l'2 constitute tuned circuits which, when
short-circuited by the upper contact of springs 55.
all station keys are normal, are tuned to the fre
Assume further that a person‘at station A desires
quency of the receiving channel individually as—
to communicate with someone at station E. To
signed to station A. Station A further comprises
this end, key 30- is operated prior to removal of
a ringer 6-2 for giving an audible signal when sta
the receiver to determine whether or not the
tion A is idle and is being called by another sta
called station is busy. The depression of key 38
tion, a busy lamp 63 for giving the subscriber at
actuates contacts 31, 38,139 and 55. The closing
station A a busy signal if the station with which
of' contact‘ 37 connects condenser 3i in parallel
a conversational connection is desired is busy, and
with condenser H and connects condenser 32 in
a busy relay 65 for rendering the receiving and
parallel with condenser 52 thereby to tune the
transmitting circuits of station A ineffective for
receiving circuits and detector of station A to the
communication in case the handset is removed
frequency of the transmitting channel individual
from the cradle while a station key is depressed
to the called station B. The actuation of springs
andthe called station is busy. Station A further
55 opens the short-circuit across the tuned circuit
comprises a gas-?lled discharge tube 6| for con
comprising coil ‘H and condenser 73, and the
trolling the ringer 52, lamp 63 ‘and relay 55, and
comprises a power ?lter consisting of retard coil
parallel
closing of
with
contact
condenser
3%’ connects
‘#3 thereby
condenser
to tune the
33 os
90 and condenser $3 for supplying power to sta 40
cillator
88
to
generate
a
carrier
current
of
the
tion A. While the telephone handset is in nor
frequency of the receiving channel individual to
mal position in the supporting cradle, the con
station B. The actuation of springs 55 also opens
tacts I'9 are open and the ?laments of tubes i5,
the normally closed circuit path through ringer
80'- and B5 are deenergized.
62 and connects the winding of busy relay 55 and
’ Only two station keys are shown in the draw
lamp 63 to conductor 92. If station E is busy
ing, key 36 for operation on a call to station E
when key 38 is- operated, carrier current of the
and key M) for operation on a call to station X.
frequency of the transmitting channel individual
As many more keys are provided as there are
to station B is being transmitted therefrom over
other stations. While the telephone handset is
in normal position in the supporting cradle, any 50 the common medium CM, and, since the receiving
network comprising transformer it? and con
of the station keys may be operated; but removal
denser I I' has been tuned to this frequency, a suf
of the handset actuates a locking mechanism
ficiently high potential is thereby applied through
which lock-3 any key which was operated at the
resistor 60 to the control element of tube 6! to
time of removal and which prevents the operation
cause breakdown of the tube and energization of
of any key subsequent to removal of the handset.
busy lamp 53' and busy relay 55. The subscriber
This locking mechanism comprises a locking plate
at station A will thereupon release the key as
24' having openings 35. 6.6 through which the
without removing‘ ‘the handset from the cradle.
plungers of the various keys project. The plate
If, however, the subscriber ignores the busy lamp
is supported‘ horizontally between bearings 25 and
signal and removes the handset, the subscriber
is movable therein under the control of an actu
at station A is unable to communicate with sta
ating element 20‘ which engages the bent over end
tion B because relay 65 holds open the receiver
of the plate. The actuating element 28 is pivoted
circuit and‘ the filament circuit through resistor
at 23 and‘, while the handset is in the cradle, the
54. If station 13 is idle, lamp 63 is not lighted
horizontal portion. of element 21% is depressed
against the compression of spring 2! against the‘ 65 and relay 55 is not operated; and the calling sub~
scriber thereupon proceeds to remove the hand
stop 22; and the locking plate is held in its ex“
set from the cradle while holding key 3!! de
treme left-hand position in which the locking col“
pressed, thereby locking‘ key 30 in its operated po
laws 35,. 45 on. plungers 34, 44 are in alignment
withthe openings 35, 45 so that any one of the
sition until the handset is replaced. The actua
station keys may be actuated. The actuation. of 70 tion of contact 19 closes the ?lament energizing
circuit through resistor 64 and the actuation of
any station key closes the associated contact
springs and also depresses the common element
springs 55 opens the normally closed short-circuit
across condenser 1.3; and with condenser 33 con
50 to actuate the contact springs 55, the element
5|]v being pivoted at 5.41 and normally held by spring
nected in parallel withcondenserlii, tube 89 gen
5-l against the stop 52. When‘ the handset is. out 75 erates carrier current of the frequency of‘ there
2,408,085 '
5
6
ceiving channel’ass‘igned individually to station
resistor 64, and front contact of ringer 62 to'con
ductor 66, thereby causing the deenergization of
tube Bl. to interrupt the energization of ringer 62.
.
B5?‘ This carrier current is modulated by the
speechfoscillations produced in transmitter I‘!
and the modulatedxcarrier current istransmitted
through ampli?er-85 and the common medium to
station B. Tube 80 also generates current of ‘the
frequency of the transmitting channel assigned
individually to station A and this current is trans
mitted through ampli?er 85 and common medium
As soon as the ringer 62 deenergizes, 'the shunt
circuitth'roughresistor 64 is opened and tube GI
again breaks down to 'reenergiz'e ringer 62. Thus
ringer 62 is alternately energized and deenergized
to give an audible calling signalias long as. car
rier current of the receiving frequency of station
CM to operate the busy lamp and'relay at any 10 A is ‘being transmitted over the common medium
CM and the handset at station A is in normal
other station at which the station A key may
position. When the handset at station ‘A is‘ re
thereafter be operated, to indicate to any other
subscriber who may wish to communicate with
station A, that station A isbusy and to prevent "
moved from the cradle to answer the call, a shunt
circuit is closed by contacts l9 through resistor
any'such subscriber from communicating with 15 64 thereby effecting the deenergization of tube
6| andpreventing its reenergizationwhile a con
station A and to preventany such subscriber
from hearing the conversation betweenstations
versational connection is maintained between sta
tion A and the calling station. While'th'e hand
Aland B. When conversation with station B is
completed, the handset is replaced in the cradle
set is removed at station A, the oscillator-modu
thereby opening contact If! to deenergize'tubes 20 lator tube 80 generates current of the frequency
I5, 80 and 85; The replacing of the handset also " > of the transmitting channel assigned individually
to station A, . this current being modulated by
restores elements I8’, 20‘ and 24 to normal posi
speech, ampli?ed by tube .85 and transmitted over
tion thereby unlocking key 30; and the return of
conductors | and 2v to the calling station. If the
key 30 to normal‘ opens contacts 31,38 and 39 and
station key corresponding to station A is depressed.
e?‘ects'the restoration of springs 55 to normal
position; Since carrier current of the frequency
at another station while station A is busy on a call
of the transmitting channel individually assigned
from a ?rst one of the other stations, the carrier
current "being transmitted from station A will
to. station A is no'longer being transmitted there
effect the energization of the busy lamp and busy
from, any other station may now establish com
munication with station A by depression of the 30 relay at this other station and prevent the sub
scriber thereat from interfering withor hearing
corresponding station key and removal of the
the conversation between station and said first
other station. When the handsets are restored
at both the calling station and at station A, sta
are normal, the ringer 62 is connected to one or
the two main electrodes of the gas-?lled discharge 35 tion A is rendered selectable for communication
handset from normal position.
’ '
.When the handset and station keys at station A
tube 6|, the control element of tube 61 being con
nected through the primary winding of trans
former I!) to conductor l of the common trans—
with any other calling station.
What is claimed is:
-
.
1. In a telephone system,'subscribers’ stations,
mission medium and through-condenser 'H to
1 a wide band transmission medium interconnect
conductor 2 of this medium. With none of the 40 ing said stations and constituting a plurality of
station keys operated, the'primary winding of
transformer “land condenser H are, tuned to the
frequency of the receiving channel individually
' channels each of a different particular frequen
cy, a pair of said channels being individually as
signed to each of said stations, one channel of
the pair assigned to each station being used for
assigned to station A. When carrier current of
this ‘frequency is transmitted [over conductors !
and 2 ‘from some calling station, responsive to
transmittingspeech to and the other channel of '
operationof the key corresponding to station A
and removal of the receiver, the impedance of
fered by the primary Winding of transformer H!
and condenser l I to‘ current of ‘this particular
frequency is low enough to cause to be impressed
mitting means at .each of said stations, the trans
mitting'means at each station comprising a car
rier. source of the frequency of the assigned in-'
on the control electrodes of discharge'tube 6| a
highenough voltage to effect the breakdown of
tube 61. The voltage similarly and simultane
ously impressed on the control electrodes of the
the pair being used for receiving speech from any
other calling station, receiving means and trans
dividual transmitting channel and a carrier
source of variable frequency, means at each sta
- tion normally tuning the receiving means there;
at to the frequency of the assigned individual re
, ceiving channel and normally tuning the variable
carrier source thereat to the frequency of the as
signed individual transmitting channel, means at‘
each station for tuning the carrier source of vari-'
discharge tubes at other idle stations is insuf
ficient to effect the breakdown of the discharge
tubes thereat because the corresponding trans
former windings and condensers at each of these
able frequency thereat to the frequency of the
stations offer a high impedance to current of the 60 receiving channel assigned individually to any‘
frequency of the receiving’ channel individually
other station with‘ which communication ‘is de-’
assigned station A. When tube 6| breaks down,
sired and for tuning the'receiving means thereat
the ringer 62 is actuated in a circuit traced from
to the frequency of the transmitting channel as
the positive pole of battery 5, conductor 2, right
signed individually to any other station with
winding of retard coil 90, conductor 92, lower ‘
which communication is desired, and signal
normally closed contact of spring-s55, windings
,means at each station normally responsive to
of ringer 62, main electrodes of tube 6|, conductor
carrier current of the frequency of the assigned
66, ?laments of tubes 85, 83 and i5 in the order
individual receiving’ channel.
7
named, conductor 9|, left winding of retard coil
' 2., In a 'telephone'system, subscribers’ stations,‘
90 *and conductor l to the negative pole ofbat
a wide band transmission medium. interconnect
tery 5;", The ?laments of' the tubes 85,‘ 8!! and
ing said stations'and constituting a plurality of. .
15. are .energized bythe current in this circuit to
carrier channels each. of a different frequency,
prepare forthe reception‘ and transmission of‘
each- of said stations having individually'rassigned
speech currentsQWhen ringern62 is energized'it.
thereto; for. use on a, call from any other of said"
closes a shunt circuit from conductor 92, through "5. stations, one‘ of said channels as a, receiving:
2,408,085
7
channel and another-of said channels as a trans
mitting channel, receiving means at each of said
stations normally tuned to the frequency of its
assigned individual receiving channel, transmit
ting means at each of said stations comprising a
carrier source tuned to the frequency of the as
signed individual transmitting channel and a
carrier source tunable to the frequency of any
one of the receiving channels assigned individu
3
assigned individual receiving channel, means at
each of said stations for tuning the receiving
means thereat to the frequency of the transmit
ting channel individual to any other station with
which communication is desired, transmitting
means at each of said stations comprising a car
rier source tuned to the frequency of the assigned
individual transmitting channel and a carrier
source tunable to the frequency of any oneof the
ally to the other stations, and signal means at 10 receiving channels assigned individually to the
other stations, signal means at each of said sta
each of said stations normally responsive to car
tions normally responsive to carrier current of
rier current of the frequency of the assigned in
the frequency of the assigned individual receiv
dividual receiving channel.
ing channel, other signal means at each of said
3.v In a telephone system, subscribers’ stations,
a wide band transmission medium interconnect 15 stations for responding to carrier current of the
frequency of any one of the transmitting chan
ing said stations and constituting a plurality of
nels individually assigned to the other stations,
carrier channels each of a different frequency,
and means at each of said stations for tuning
each of said stations having individually assigned
said other signal means to the frequency of the
thereto, for use on a call from any other of said
transmitting channel which is individual to any
stations, one of said channels as a receiving
particular one of the other stations with which
channel and another of said channels as a trans
communication is desired.
mitting channel, receiving means at each'of said
6. In a telephone system, subscribers’ stations,
stations normally tuned to the frequency of its
assigned individual receiving channel, trans
a wide band transmission medium interconnect
mitting means at each of said stations compris 25 ing said stations and constituting a plurality of
carrier channels each of a different frequency,
ing a carrier source tuned to the frequency of the
each of said stations having individually assigned
assigned individual transmitting channel and a
carrier source tunable to the frequency of any
thereto, for use on calls from another of said sta
tions, one of said channels as a receiving channel
one of the receiving channels assigned individu
ally to the other stations, signal means at each 30 and one of said channels as a transmitting chan
nel, a telephone receiver at each of saidv stations,
of said stations normally responsive to carrier
means at each station comprising demodulating
current‘of the frequency of the assigned indi
means connecting the receiver thereat to said
vidual receiving channel, other signal means at
common medium, a busy relay and‘ a busy signal
each of, said stations for responding to carrier
current of the frequency of any one of the trans 35 at each station, control means at each station
mitting channels individually assigned to the
connected to said common medium for control—
ling the operation of the busy relay and signal
other stations, and means at each of said sta
tions for tuning said other signal means to the
thereat, the control means at each station nor
mally operatively tuned to the frequency of the
frequency of the transmitting channel which is
assigned individual receiving channel of the sta
individual to any particular one of the other sta
tions with which communication is desired.
tion, keys at each station, one for each other sta
tion, means at each station rendered effective by
4. In a telephone system, subscribers’ stations,
the operation of any one of the keys thereat for
a wide band transmission medium interconnect
operatively connecting the busy relay and busy
ing said stations and constituting a plurality of
signal thereat in circuit with the control means
carrier channels each of a different frequency,
each of said stations having individually as
thereat, and means individual to each of said keys‘
at each station for tuning the connection be~
signed thereto, for use on a call from any other
of said stations, one of said channels as a receiv
ing channel and another of said channels as a
tween the common medium and the control
means thereat to the frequency of the transmit
transmitting channel, receiving means at each of 50 ting channel assigned individually to the station
corresponding to any operated key.
said stations normally tuned to the frequency of
its assigned individual receiving channel, means
'7. In a telephone system, subscribers’ stations,
at each of said stations for tuning the receiving
a wide band transmission medium interconnect
ing said stations and constituting a plurality of
means thereat to the frequency of the transmit
ting channel individual to any other station with 55 carrier channels each of a different frequency,
which communication is desired, transmitting
each of said stations having individually assigned
means at each of said stations comprising a car
rier' source tuned to the frequency of the as
thereto, for use on calls from another of said
stations, one of said channels as a receiving chan-
signed individual transmitting channel and a
nel and one of said channels as a transmitting‘
carrier source tunable to the frequency of any 60 channel, a telephone receiver at each of said Staone of the receiving channels assigned individu
tions, means at each station comprising demodu
ally to the other stations, and signal means at
lating means connecting the receiver thereat to
each. of said stations normally responsive to car
said common medium, means at each station
rier current of the frequency of the assigned
normally tuning the demodulating means there
individual receiving channel.
65 at to the frequency of the assigned individual re
5. In a telephone system, subscribers’ stations,
ceiving channel, a busy relay and a busy signal at
a wide band transmission medium interconnect
each station, control means at each station con
ing said stations and constituting a plurality of
nected to said common medium for controlling
the operation of the busy relay and signal there
carrier channels each of a different frequency,
at, the control means at each. station normally
each of said stations having individually assigned
operatively tuned to the frequency of the as
thereto, for use on a call from any other of said
stations, one of said channels as a receiving
channel and another of said channels as a trans
mitting channel, receiving means at each of said
stations normally tuned to the frequency of its
signed individual receiving channel of the station,
keys at each station, one for each other station,
means at each station rendered effective by- the
operation of any one of the keys thereat for op-
2,408,085
10“
eratively connecting the busyrelay and busy sig-}; mitting channelgassign'ed to any other station
nal thereatin circuit with the control means
with whichcommunication is desired, thereby to
effect the energization of the busy signal‘ and
thereat, means individual to'each of said keys
at :each station for tuning the connection ‘be
busy relayvzat any calling station responsive'to
carrier current of the frequency of the individual
transmitting channel of, the station with which
tween the common medium and the control
means thereat to the frequency of the transmit
ting channel assigned individually to the station
corresponding‘to any, operated key, and contact
communication is desired, and means at each sta
tion for transmitting a carrier of the frequency
means at each station actuated by the energiza
of the individual transmitting channel whenever
‘
~
tion of said relay thereat, when the station corre 10 the station is busy.
sponding to an operated one of the keys is'busy,
10. On a telephone system, subscribers’ stations,
for disabling the receiver thereat:
a Wide band transmission medium interconnect
8. In a telephone system, subscribers’ stations,
ing said stations and constituting a plurality of
a wide band transmission medium interconnect
carrier channels each of a different frequency,
ing said stations and constituting a plurality of 15 each of said'stations having individually assigned
carrier channels each of a di?erent frequency,
each of said stations having individually assigned
thereto for use on calls‘ to said station from any
other station one of said channels as a receiving
channel and one of said channels as a transmit
thereto for use on calls from another of saidsta
tions one of said channels as a receiving channel
and one of said channels as a transmitting chan
nel, a telephone receiver at each station, means
ting channel, a source of power common to ‘said
stations and connected thereto by the conductors
of said common transmission medium, each of
at each station comprising demodulating means
connecting the receiver thereat to said common
medium, means at each station normally tuning
said stations comprising a telephone receiver and
the demodulating means thereat to the frequency a
of the assigned individual receiving channel, a
busy relay and a busy signal at each station, con
trol means at each station comprising a gas-?lled
transmitter, means comprising -a detector tube
connecting said receiver to said common medium,
a ringer, a busy lamp, a busy relay, means com
prising a gas-?lled discharge tube connecting
said ringer, lamp, and relay, to said common
medium, means normally tuning the connection
discharge tube connected to said commonme
7 between said detector tube and common medium
dium for controlling the operation of the ‘busy 30 to the frequency of the receiving channel indi
relay and busy signal thereat, the control means
vidual thereto, means normally tuning the con
at each station normally operatively tuned to the
nection between said discharge tube and common
frequency of the assigned individual receiving
medium to the frequency of the receiving chan
nel individual thereto thereby to effect the
channel of the station, selective means at each‘
station individual to each of the other stations
for operatively connecting the busy signal and
breakdown of said tube responsive to the trans
mission over said common medium of carrier cur
busy relay in circuit with the control means
rent of the frequency of said receiving channel to
thereatand for tuning the connection between
operate said ringer, an oscillator-modulator tube;
the discharge tube thereat and common medium
means in the oscillatory control circuit of said
to the frequency of the individual transmitting 40 oscillator-modulator tube tuned to the frequency
channel assigned to any other station with which
of the individual transmitting channel, other
means in the oscillatory control circuit of said
communication is desired, thereby to enable the
energization of the busy signal and busy relay at
oscillator-modulatortube tunable to the frequen
'
a calling station responsive to carrier current of
cy of the individual receiving channel of any of
the frequency of the individual transmitting 45 the other stations, contacts normally short-cir
channel of the station with whichcommunica
cuiting said other means, means comprising an
ampli?er connecting the output of said oscillator
tion is desired.
,
modulator tube to said common medium, means
9. In a telephone system, subscribers’ stations,
connecting said transmitter to said oscillator
a wide band transmission medium interconnect
ing said stations and constituting a plurality of 50 modulator tube to modulate the oscillatory cur
rent generated in said tube, circuit means includ
carrier channels each of a diiferent frequency,
ing said power source rendered e?ective by the
each of said stations having individually assigned
operation of said ringer and by the removal of
thereto for use on calls from another of said
the receiver from normal for energizing said
stations one of said channels as a receiving chan- nel and one of said channels as a transmitting 55 detector and ampli?er and oscillator-modulator
tubes, calling keys, one for each of the other sta
channel, a telephone receiver at, each station,
tions, means individual to each of said keys and
means at each ‘station comprising demodulating
rendered effective by operation of the key to tune
means connecting the receiver thereat to said
common medium, means at each station normally
the connection between said common medium ‘
tuning the demodulating means thereat to the 60 and the detector tube and the connection between
said common medium and'said discharge tube to
frequency of the assigned individual receiving
the frequency of the transmitting channel indi
channel, a busy relay and a busy signal at each
vidual to the station corresponding to the oper
station, control means at each station compris
ated key and to tune said other means in the os
ing a gas-?lled discharge tube connected to said
common medium for controlling the operation 65 cillatory control circuit of said oscillator-modue
lator tube to the frequency of ‘the receiving chan
of the busy relay and busy signal thereat, the con- '
nel individual to the station corresponding to
trol means at each station normally operatively
the operated key, means responsive to the opera
tuned to the frequency of the assigned individual
tion of any of said station keys for opening the
receiving channel of the station, selective means
at each station individual to each of the other 70 operating circuit of said ringer and for connect
stations for operatively connecting the busy sig
nal and busy relay thereat in circuit with the con
trol means thereat and for tuning the connection
between the discharge tube thereat and common
medium to the frequency of the individual trans
ing said lamp and relay for operation responsive
to transmission over said common medium of car
rier current of the frequency of the transmitting
channel individual to the station corresponding
76 to the operated key, means actuated by the ener
‘2,468,686
11
gization of saidrelay for preventing the energi
zation of said tubes and receiver, means respom
sive to the operation of any of said keys for open
ing said contacts normally shortecircuiting ‘said
other means in the oscillator control circuit of
said oscillator-modulator tube, locking mecha
nism common to said keys normally positioned to
allow the operation of any key, and means actu
12
atingsaid locking mechanism responsive to‘ the
removal of‘ the receiver from norma1 position to
prevent the operation of any of‘ said keys While
said receiver is’ elf-normal and‘ to lock operated
" any key which is operated at the time‘ of re
moval of the receiver from normal.
LARNED A. MEACHAM.
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