Improvements in Telephone Systems and Apparatus.
Year: 1899

page_text: Date of Application, 12th Dec., 1899
Complete Specification Left, 9th Oct., 1900-Accepted, 12th Dec., 1900
PROVISIONAL SPECIFICATION.
Improvements in Telephone Systems and Apparatus.
I, JOHN EDWARD KINGSBURY, of 79, Coleman Street, in the City of London,
Manager, do hereby declare the nature of this invention (which has been com-
municated to me from abroad by The Western Electric Company, of Chicago,
Illinois, United States of America,) to be as follows:-
This invention relates to improvements in telephone systems especially in cases
where the electric current for signalling and energising the telephone instruments
or for either purpose separately is derived from a source common to a number
of telephone lines.
The improvements shown in Figure 1 relate to improvements in the circuit
at a subscribers station.
1 and 2 are the lines from the exchange. A is the transmitter, B the receiver,
Ca condenser, 1) a bell or other signalling apparatus and E an induction coil
with three windings c', e², e³.
Hitherto in nearly every type of transmitter, especially when employed in the
form of hand telephones, it has been found that when these are employed in con-
nection with a system worked by electric energy from a central source trouble
results which materially diminishes the efficiency of such systems. One fault
has been that when the circuit has been closed through the transmitter the resist-
ance of the transmitter has been sufficiently high to prevent the
proper working of the signalling apparatus at the exchange. Another
defect has been that the transmission of speech has been injuriously
affected by too large a current passing through the transmitter. Both these
faults can be remedied by inserting a resistance in shunt with the transmitter
and in order that this shunt shall not appreciably reduce the transmission of
speech and at the same time not be of too high resistance to effect its object,
this according to this invention is made to offer considerable impedance to
fluctuating currents by winding it on an iron core.
In Figure 1 this shunt forms a third circuit of the induction coil and this
arrangement has the further advantage of reducing the objectionable effect of the
transmitter action upon the receiver which is associated with it. This effect is
generally known to telephone experts as "side tone."
In Figure 1 the shunt around the transmitter is shown wound separately and
is represented by F', the other parts of the circuit being lettered as in Figure 1.
In telephone systems it is not unusual for stations to be connected with the
exchange and also to be provided with lines to one or more sub-stations. If
these lines to the sub-stations are allowed to communicate with the exchange they
are usually called "exchange "extensions," and if debarred from this communica-
tion private extensions."
By means of this invention the current for signalling purposes, as well as for
energising the transmitters or speaking apparatus, can be derived from the
exchange thereby avoiding the necessity for local batteries or other sources of
electric energy.

page_text: Figure 2 shows a circuit and apparatus for working a single exchange extension
line. At the exchange A one of the lines 1 of the metallic circuit 1, 2 is connected
through a resistance a and through the contact a, a, of the cut off relay a to
the battery or other source of electric energy the other line 2 being connected
through the contact a³, at, of the cut off relay a to the calling relay the other
side of which is connected to ground.
This
At the intermediate station B a bell c or other signalling apparatus is bridged
across the line, a condenser d of suitable capacity being included in the bridge.
The lines 1 and 2 are connected to the springs and e¹ of the key e.
key is normally kept thrown over so that the insulating wedge e" is between
the springs e, e, so that the contacts between these and e7, es, respectively are
broken.
In this position the exchange can ring the station B by the bell c through
the condenser d but no current flows from the exchange battery b as the con-
tacts e, e, f, f³, c¹, c², k¹, k³, n¹, n³, are all broken and the condensers d, ft and 64
form a barrier to the continuous current.
Station B can call the exchange by removing the telephone f off the hook f'.
The current from the exchange battery then flows through the contact a¹, a², the
resistance a, the line 1, the contact c, e, the conductor 3, the transmitter f, the
contact, f, the conductor 4, the contact e³, e, the line 2, the contact ³,, and
the relay a back to the earthed side of the battery b. This excites the relay a³
which closes and lights the lamp a.
When the operator at A replies, the cut-off relay a is operated and this cuts
of the battery 6 but, as the battery is also connected to the operators cords, it
is again connected.
Station B can call station C by means of the key k and the biassed bell m, the
latter being actuated each time the contact K¹ is made. The current from
the exchange battery is then through the contact a², a¹, the resistance a, the
line 1, the conductor 5, the impedance coil 1, the conductor 6, the con-
tact 3, k, the line 7, the contact n', n², and through the bell m to earth. In the
same manner station C can call station B by means of the key N and the bell J
which is also biassed.
To enable station B to speak to station C it is necessary for B to reverse the
position of the key e so that the insulating wedge ell is between the springs el
and e lifting these off the contacts e3, 4, and forcing the springs against
the contact e10. It will be seen that connection is now established between the
instruments f and c, through the contacts e, e, and e³, e, and the lines 7
and 8, and that a current from the exchange battery will flow through the
contact a, a, the resistance a, the line 1, the conductor 5, the impedance coil ¹
the conductor 6 to the line 8, where it will divide a portion flowing through
the transmitter c, the induction coil 2, the line 7, the contact the con-
tact ele and the impedance coil 2 to ground and a portion through the con-
tact ees, the conductor 3, the transmitter, the induction coil f, the conductor 4,
the contact e, e, and also through the contact e, e, and the impedance coil ²
to ground. The transmitters will then be energised and communication is estab-
lished between the two stations. The windings of the impedance coils h¹² are
preferably placed around the same core.
Should station C wish to communicate with the exchange station B puts the
insulating wedge of key e in the middle position so that the springs el, c², e, e,
all rest on the contacts e, e, e', es, respectively.
It will be seen that lines 1 and 2 are joined through to lines 7 and 8 and
consequently C can speak to the exchange A and obtain any desired connection.
Station B replaces his telephone on the hook if it is not required that he should
listen and gives the attendant at station B the signal to disconnect by operating
the key n thus ringing the bell J, station B then restores key e to its normal
position.
Figure 3 shows a circuit and apparatus for working a single private extension.

page_text: The connections and apparatus at the exchange are similar to those shown in
Figure 2 and need not again be described. A bell, or other signalling apparatus c
and a condenser d are bridged across the line at the intermediate station Bas
before described.
The lines 2 and 1 are connected to the contacts e², e³, of the key e, and normally
are in connection with the springs e³ and 'e respectively and consequently are
connected with the instrument f by the conductors 3 and 4 so that station B can
call and he called by the exchange A as previously described.
The calling between B and C is also similar to that shown in Figure 2. To
speak with station C station B reverses the position of the kev e breaking the
contacts e¹, e³, ea, e*, and forcing the spring against the contact e¹a and the spring e
against the springs e and e10. Communication is thus established between the
two stations B and C and the transmitters are energised substantially as before
described.
It will be seen from a study of the diagram that the key e at station B
cannot be manipulated in such a manner as to put station C into connection with
the exchange A.
Figure 4 shows circuits and apparatus for working several extension lines
either exchange or private, or both.
<<
"
The connections and apparatus at the exchange are similar to those previously
described, and are marked with the same letters for convenience. At the inter-
mediate station B, which is generally known as a private branch exchange'
when there are several extensions, a switchboard is employed with means for con-
necting the lines together. Various automatic methods may be used but it is
preferred to employ spring jacks in combination with suitable plugs and cords and
apparatus for signalling generally known as visual indicators.
In the diagram the two sides of the line to the exchange 1 and 2 are connected
to a jack e, a signalling apparatus c and a condenser being bridged across the
line as before described. Line 1 is connected to the spring e¹ and also to one
side of a combination of impedance coils and condensers, the use of which will
be described later.
Line 2 is connected to the contact ct of the jack e and is only in contact with
the spring when a plug is inserted into the jack e. The springe is also con-
nected with the series of impedance coils and normally rests on the contact e³
which is connected to ground. The arrangement of impedance coils and con-
densers may be varied, but it is found that the best results are obtained by the
combination as shown, the condensers s¹, 2, 3 being bridged across the line
at points intermediate in the series of coils rl, pa², pu³, job, job, p6, 7, 8. Very good
results may be obtained with an ohmic resistance of 56 ohms in each coil which
should be of high impedance and a capacity of two microfarads for each con-
denser. This combination enables the current from the exchange battery to be
used for energising the transmitters in different circuits at the private branch
exchange simultaneously without overhearing, which would take place if these or
similar precautions were not taken.
The connections and apparatus at the extension station may be such as are
usually employed with systems using a common source of electric energy situated
at the exchange. Two such stations C and C are shown on the diagram, the
instrument connections being identical but the connections and apparatus at the
intermediate station B being different as C represents an exchange extension and
C¹ a private extension. At private branch exchanges of this character it is usually
required that some of the extension stations be permitted to speak with the main
exchange as well as to all or any of the other extensions. A portion of the
extension stations however are debarred from communicating with the main
exchange although they may have free access to all the other extensions. The
method shown on the diagram for attaining this end consists of the employment
of spring jacks with openings of two different sizes together with two groups of
plugs of different size adapted to work in conjunction with the above described

page_text: the springs
provided with two jacks one of each size to permit
The lines 7, 8 of the extension C are connected to
which normally rest on the contacts
jacks. The exchange lines are
of this method of operation.
of the jack
these
being connected to the springs. ¹ y² of the jack which normally rest on the
contacts ³y. The contact is connected through the visual indicator J to
at the exchange through the conductors 9 and 5
the source of electric energy
and the impedance coils 24, 73, 72, 7 as previously described.
The lines 13, 14 of the private extension C are connected to the springs y y
of the jack and these rest normally on the contacts 7, 8, the former being
connected by the conductor 12 to the conductor 6 and the latter through the visual
indicator by the conductor 11 to conductor 5. These conductors 5 and 6 are
connected as before described to the battery b through the special impedance
coils.
The contact is joined by conductors 10 and 6 to ground through impedance
coils 7 p p conductor 4 spring of the jacke and then if no plug is inserted in
jack e to the contacte and to ground through conductor 17, should there be a plug
in jacke the current returns to the battery at the exchange A through the line 2.
A pair of cords for connecting exchange extensions with the exchange is shown
in the diagram and for convenience should be provided with a listening key a
for throwing in and out of circuit the telephone instrument f and a ringing key k
for connecting the source of ringing current 7. A visual indicator J2 may be
included in the circuit of the cord the plug of which is inserted in the extension
line jack as a clearing signal. In order that the control of the exchange con-
nection may be in the hands of the attendant at station B, which is considered
to be the most desirable arrangement, each pair of cords employed for this ser-
vice is equipped with an impedance coil p joining its two line conductors. The
effect of this is to establish a circuit connection between the lines 1 and 2 of the
exchange line as long as one of the plugs is in jack e so that the supervisory
or clearing signal at the exchange A is not displayed. When the plug is removed
from jack e this circuit connection between lines 1 and 2 no longer exists and
notification of this disconnection is thereby automatically given by the operation
of the supervisory signal which may be associated with the lines 1 and 2 at the
exchange A. The supply of current to the cord circuit for energising the trans-
mitter of the extension line with which the attendant at B is in communication
is obtained from the exchange battery through the special impedance coils ¹, etc.
and conductor 5 and 6 to which are joined lines 18 and 17 which include in their
circuit the two impedance coils 10 and connect with conductors 20 and 19.
These conductors are brought into connection with the cord circuit when the
kev g
is actuated. The cords employed for establishing connection between
extensions may be very similar to those just described, but in their case it is
preferred to join the impedance coils through which the current supply is obtained
direct to the cord circuit without the intervention of the listening key and to
include the clearing signal in one of these connections in order that the signal
may not be displayed until both extensions have hung up their receivers. The
impedance shunt between the two conductors is also omitted. A switching key h
is provided to connect the operators instrument f with either group of cords. If
this were omitted it would be possible for the operator at B to join the two groups
together by connecting both at the same time to her telephone instrument. A
condenser 3 is placed in circuit with the receiver f¹ and induction coil f³, in order
to avoid a wasteful flow of current through this circuit.
The operators transmitter f is energised by the current from the exchange
line through the impedance coils 1, 2, 3, 6, 7, 8, and the conductors 5
and 6.
An impedance coil f is placed in series and a condenser f5 in shunt with
the transmitter f and induction coil fi to prevent overhearing between this
instrument and the other lines.
The exchange can ring station B by the bell c through the condenser d.

page_text: Station B can call the exchange by inserting the plug into the jack e. The
current from the exchange battery then flows through the contact a¹ a³ the
resistance a the line 1 the spring e' of the jack e the sleeve 7 of the plug the
conductor 15 the shunt p the conductor 16 the tip 73 of the plug 7' the contact e² et
of the jack e the line 2 and the relay a back to the earthed side of the battery b.
This excites the relay which closes and lights the lamp a.
When the operator at A replies the cut-off relay e is operated and this cuts
off the battery b, but as the battery is also connected to the operators cords it
is again connected. For station B to speak to the exchange it is necessary that
the listening key should be actuated so that the springs are against
the contacts g3 g and then if the key h is also in such a position that springs h¹ h
are against contacts h³ the telephone f the induction coil and the con-
denser fare in circuit with the exchange line and as the transmitter f* is
energised as before described conversation can take place.
The extensions C, C¹ can call station B by removing the receiver off the hook
thus forming a path for the current from the exchange battery
through their respective transmitters and actuating the visual signals
at station B. In the case of the exchange extension C the current from
the battery flows through the contact a¹ a² the resistance a the line 1 the con-
ductor 3 the impedance coils 1, 2, 3, 4, the conductors 5 and 8 the visual
indicator J the contacts y y² and the conductor 8 the transmitter of the
contact the conductor 7 the contacts a³ and y¹y the conductor 10 and 6
the impedance coils the conductor 4 the contact e²e and to ground
through the conductor 17. Should a plug be in the jack e the spring is in
contact with e and the current flows back to the grounded side of the battery b
through the line 2. the current through the visual indicator J actuates it and
gives the calling signal. To speak to the calling extension B inserts a plug 72
into the jack and manipulates the listening keys thus establishing connection
with his telephone instrument. Should C wish to communicate with the
exchange B inserts the plug Z into the jack e and this automatically signals the
exchange. B then disconnects the telephone instrument f from the cord circuit
by manipulating the listening key g. As long as the receiver at C is off the
hook the visual signal J2 is displayed but directly C replaces his receiver this
signal automatically is restored to its normal position. This notifies B that the
connection may be removed and when the plug Z is removed from the jack e
the exchange operator at A is automatically advised of the fact as previously
described.
In case C desired to communicate with the private extension C¹ instead of
with the exchange, the attendant at B after ascertaining this establishes the
desired connection by means of a pair of plugs W1 W2 included in the group
provided for this purpose calling the station wanted by means of the ringing
key. The signal associated with this pair of cords serves to automatically advise
the attendant at B to remove the connection when the receivers at both stations
have been replaced on the hook.
While I have described a particular method for carrying out the improvements
it is to be understood that the scope of the invention is not to be restricted to the
specific plans described.
COMPLETE SPECIFICATION.
Improvements in Telephone Systems and Apparatus.
I, Jonx EDWARD KINGSBURY, of 79, Coleman Street, in the City of London,
Manager, do hereby declare the nature of this invention (which has been com-

page_text: municated to me from abroad by The Western Electric Company, of Chicago,
Illinois, United States of America,) and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement:
-
This invention relates to improvements in telephone systems especially in cases
where the electric current for signalling and energising the telephone instruments
or for either purpose separately is derived from a source common to a number
of telephone lines.
The improvements shown in Figure 1 of the drawings lodged with the Pro-
visional Specification relate to improvements in the circuit at a subscribers
station.
1 and 2 are the lines from the exchange. A is the transmitter, B the receiver,
C a condenser, D a bell or other signalling apparatus and E an induction coil
with three windings e¹, e³, e³.
Hitherto in nearly every type of transmitter, especially when employed in the
form of hand telephones, it has been found that when these are employed in con-
nection with a system worked by electric energy from a central source trouble
results which materially diminishes the efficiency of such systems. One fault
has been that when the circuit has been closed through the transmitter the resist-
ance of the transmitter has been sufficiently high to prevent the
Another
proper working of the signalling apparatus at the exchange.
defect has been that the transmission of speech has been injuriously
affected by too large a current passing through the transmitter. Both these
faults can be remedied by inserting a resistance in shunt with the transmitter
and in order that this shunt shall not appreciably reduce the transmission of
speech and at the same time not be of too high resistance to effect its object,
this according to this invention is made to offer considerable impedance to
fluctuating currents only by winding it on an iron core.
In Figure 1 this shunt forms a third circuit of the induction coil and this
arrangement has the further advantage of reducing the objectionable effect of the
transmitter action upon the receiver which is associated with it. This effect is
generally known to telephone experts as side tone."
6
In Figure 1 of the drawings lodged with the Provisional Specification the
shunt around the transmitter is shown wound separately and is represented by F,
the other parts of the circuit being lettered as in Figure 1.
An alternative circuit which gives good results with transmitters and receivers,
which have not been specially constructed to be actuated by electric energy from
a central source, is shown in the accompanying Figure 1. In this case the shunt
is connected across the terminals of the receiver. The transmitter is energised
by the current from the central source through line 1 the shunted receiver B
the windings ee of the induction coil E and the line 2. A bell D is joined
between line 1 and the switch-hook and a condenser C between the switch-hook
and line 2. This condenser besides serving a useful purpose by acting as a barrier
to continuous currents, improves the transmission of speech by forming a local
circuit consisting of the condenser, transmitters and winding e² of the induction
coil and the undulations caused by the variation in resistance of the transmitter
when being spoken into are transmitted inductively as well as serially through
the winding and out to line.
In telephone systems it is not unusual for stations to be connected with the
exchange and also to be provided with lines to one or more sub-stations. If
these lines to the sub-stations are allowed to communicate with the exchange they
are usually called "exchange extensions," and if debarred from this communica-
tion private extensions."
By means of this invention the current for signalling purposes, as well as for
energising the transmitters or speaking apparatus, can be derived from the
exchange thereby avoiding the necessity for local batteries or other sources of
electric energy

page_text: Figure 2 of the drawings lodged with the Provisional Specification
shows a circuit and apparatus for working a single exchange extension
line. At the exchange A one of the lines 1 of the metallic circuit 1-2 is connected
through the resistance a and through the contact a 2 of the cut off relay a to
the battery or other source of electric energy the other line 2 being connected
through the contact a³ at of the cut off relay a to the calling relay the other
side of which is connected to ground.
This
At the intermediate station B a belle or other signalling apparatus is bridged
across the line, a condenser d of suitable capacity being included in the bridge.
The lines 1 and 2 are connected to the springs e² and e¹ of the key e.
key is normally kept thrown over so that the insulating wedge e" is between
the springs es e so that the contacts between these and 7 respectively are
broken.
In this position the exchange can ring station B by the bell through
the condenser & but no current flows from the exchange battery as the con-
tacts e efl f² c¹ c³ k¹ ks n² n³ are all broken and the condensers d f and c¹
form a barrier to the continuous current.
Station B can call the exchange by removing the telephone f off the hook f¹.
The current from the exchange battery & then flows through the contact a¹ a², the
resistance a the line 1 the contact et, the conductor 3, the transmitter f the
contact ff, the conductor 4 the contact e e¹, the line 2 the contact a³ a¹ and
the relay a back to the earthed side of the battery b. This excites the relay u
which closes and lights the lamp a.
When the operator at A replies, the cut-off relay as is operated and this cuts
off the battery b but, as the battery is also connected to the operators cords, it
is again connected.
Station B can call station C by means of the key k and the biassed bell m, the
latter being actuated each time the contact and is made. The current from
the
the exchange battery is then through the contact a² a the resistance a
line 1 the conductor 5 the impedance coil the conductor 6 the con-
tact the line 7 the contact n¹ and through the bell m to earth. In the
same manner station C can call station B by means of the key n and the bell J
which is also biassed.
To enable station B to speak to station C it is necessary for B to reverse the
position of the key e so that the insulating wedge ell is between the springs e
and lifting these off the contacts ea and forcing the spring e against
the contact eiu. It will be seen that connection is now established between the
instruments f and c through the contacts and ea and the lines 7
and 8 and that a current from the exchange battery b will flow through the
contact a a² the resistance a the line 1 the conductor 5 the impedance coil '
the conductor to the line 8 where it will divide a portion flowing through
the transmitter the induction coil 2 through the line 7 the contact the con-
tact and the impedance coil 2 to ground and a portion through the con-
tact ees, the conductor 3, the transmitter f the induction coil f³ the conductor 4
the contact ee and also through the contact ee and the impedance coil h²
to ground. The transmitters will then be energised and communication is estab-
lished between the two stations. The windings of the impedance coils h¹² are
preferably placed around the same core.
Should station C wish to communicate with the exchange station B puts the
insulating wedge of key e in the middle position so that the springs e¹² e eti
all rest on the contacts e e e e respectively.
It will be seen that lines 1 and 2 are joined through to lines 7 and 8 and
consequently C can speak to the exchange A and obtain any desired connection.
Station B replaces his telephone on the hook if it is not required that he should
listen and C gives the attendant at station B the signal to disconnect by operating
the key thus ringing the bell J. Station B then restores key e to its normal
position.

page_text: Figure 3 of the drawings lodged with the Provisional Specification
shows a circuit and apparatus for working a single private extension.
The connections and apparatus at the exchange are similar to those shown in
Figure 2 and need not again be described. A bell, or other signalling apparatus e
and a condenser d are bridged across the line at the intermediate station B as
before described.
The lines 2 and 1 are connected to the contacts e¹ e² of the key e and normally
are in connection with the springs 3 and respectively and consequently are
connected with the instrument f by the conductors 3 and 4 so that station B can
call and be called by the exchange A as previously described.
The calling between B and C is also similar to that shown in Figure 2. To
speak with station C station B reverses the position of the key e breaking the
contacts e¹ eee and forcing the spring e against the contact e¹ and the spring e
against the springs e and e¹. Communication is thus established between the
two stations B and C and the transmitters are energised substantially as before
described.
It will be seen from a study of the diagram that the key o at station B
cannot be manipulated in such a manner as to put station C into connection with
the exchange A.
Figure 4 of the drawings lodged with the Provisional Specification shows circuits
and apparatus for working several extension lines either exchange or private, or
both.
«
The connections and apparatus at the exchange are similar to those previously
described, and are marked with the same letters for convenience. At the inter-
mediate station B, which is generally known as a private branch exchange
when there are several extensions, a switchboard is employed with means for con-
necting the lines together. Various automatic methods may be used but it is
preferred to employ spring jacks in combination with suitable plugs and cords, and
apparatus for signalling generally known as visual indicators.
In the diagram the two sides of the line to the exchange 1 and 2 are connected
to a jack e, a signalling apparatus c and a condenser d being bridged across the
line as before described. Line 1 is connected to the spring e¹ and also to one
side of a combination of impedance coils and condensers, the use of which will
be described later.
Line 2 is connected to the contact e¹ of the jack e and is only in contact with
the spring when a plug is inserted into the jack e. The spring e2 is also con-
nected with the series of impedance coils and normally rests on the contact e³
which is connected to ground. The arrangement of impedance coils and con-
densers may be varied, but it is found that the best results are obtained by the
combination as shown, the condensers S1 S2 S3 being bridged across the line
at points intermediate in the series of coils R¹ R2 R3 R4 R5 R6 R7 R8. Very good
results may be obtained with an ohmic resistance of 50 ohms in each coil which
should be of high impedance and a capacity of two microfarads for each con-
denser. This combination enables the current from the exchange battery to be
used for energising the transmitters in different circuits at the private branch
exchange simultaneously without overhearing, the variations in the current being
so to speak localised in the respective circuits. Instead of condensers, impedance
coils bridged across the line effect the same purpose but the condensers prevent
waste of current, and are more convenient for signalling purposes.
The connections and apparatus at the extension station may be such as are
usually employed with systems using a common source of electric energy situated
at the exchange. Two such stations C and C¹ are shown on the diagram, the
instrument connections being identical but the connections and apparatus at the
intermediate station B being different as C represents an exchange extension and
C¹ a private extension. At private branch exchanges of this character it is usually
required that some of the extension stations be permitted to speak with the main
exchange as well as to all or any of the other extensions. A portion of the

page_text: extension stations however are debarred from communicating with the main
exchange although they may have free access to all the other extensions. The
method shown on the diagram for attaining this end consists of the employment
of spring jacks with openings of two different sizes together with two groups of
plugs of different size adapted to work in conjunction with the above described
jacks. The exchange lines are provided with two jacks one of each size to permit
of this method of operation. The lines 7, 8 of the extension C are connected to
the springs of the jack which normally rest on the contacts ³ these
being connected to the springs y₁y of the jack y which normally rest on the
contacts y³y. The contact y is connected through the visual indicator J_to
the source of electric energy 6 at the exchange through the conductors 9 and 5
and the impedance coils R R R2 R¹ as previously described.
The lines 13, 14 of the private extension C¹ are connected to the springs y³ 36
of the jack y and these rest normally on the contacts y7, y8, the former being
connected by the conductor 12 to the conductor 6 and the latter through the visual
indicator by the conductor 11 to conductor 5. These conductors 5 and 6 are
connected as before described to the battery b through the special impedance
coils.
•
The contact y³ is joined by conductors 10 and 6 to ground through impedance
coils R R R R conductor 4 spring of the jack e and then if no plug is
inserted in jack e to the contacte and to ground, should there be a plug in jack e
the current returns to the battery at the exchange A through the line 2.
A pair of cords for connecting exchange extensions with the exchange is shown
in the diagram and for convenience should be provided with a listening key g
for throwing in and out of circuit the telephone instrument f and a ringing key k
for connecting the source of ringing current 7. A visual indicator Ja may be
included in the circuit of the cord, the plug of which is inserted in the extension
line jack, as a clearing signal. In order that the control of the exchange con-
nection may be in the hands of the attendant at station B, which is considered
to be the most desirable arrangement, each pair of cords employed for the ser-
vice is equipped with an impedance coil p joining its two line conductors. The
effect of this is to establish a circuit connection between the lines 1 and 2 of the
exchange line as long as one of the plugs is in jack e, so that the supervisory
or clearing signal at the exchange A is not displayed. When the plug is removed
from jack e this circuit connection between lines 1 and 2 no longer exists and
notification of this disconnection is thereby automatically given by the operation
of the supervisory signal which may be associated with the lines 1 and 2 at the
exchange A. The supply of current to the cord circuit for energising the trans-
mitter of the extension line with which the attendant at b is in communication
is obtained from the exchange battery through the special impedance coils R¹, etc.,
and conductor 5 and 6 to which are joined lines 18 and 17 which include in their
circuit the two impedance coils R R and connect with conductors 20 and 19.
These conductors are brought into connection with the cord circuit when the
key g is actuated. The cords employed for establishing connection between
extensions may be very similar to those just described, but in their case it is
preferred to join the impedance coils through which the current supply is obtained
direct to the cord circuit without the intervention of the listening key and to
include the clearing' signal in one of these connections in order that the signal
may not be displayed until both extensions have hung up their receivers. The
impedance shunt between the two conductors is also omitted. A switching key h
is provided to connect the operators instrument f with either group of cords. If
this were omitted it would be possible for the operator at B to join the two groups
together by connecting both at the same time to her telephone instrument. A
condenser is placed in circuit with the receiver f¹ and induction coil fa in order
ic avoid a wasteful flow of current through this circuit.
The operators transmitter f' is energised by the current from the exchange

page_text: line through the impedance coils R¹ R2 R3 R4 R5 R6 R7 R8 and the condensers
and through lines 5 and 6.
An impedance coil f" is placed in series and a condenser f in shunt with
the transmitter f and induction coil 7 to prevent overhearing between this
instrument and the other lines.
The exchange can ring station B by the bell through the condenser d.
Station B can call the exchange by inserting the plug into the jack e. The
current from the exchange battery b then Hows through the contact a¹ a² the
resistance a the line 1 the spring e₁ of the jack e the sleeve Z5 of the plug Z¹ the
conductor 15 the shunt p the conductor 16 the tip Z3 of the plug Z the contact e² e¹
of the jack e the line 2 and the relay a back to the earthed side of the battery b.
This excites the relay a5 which closes and lights the lamp a.
When the operator at A replies the cut-off relay e is operated and this cuts
off the battery b, but as the battery is also connected to the operators cords it
is again connected. For station B to speak to the exchange it is necessary that
the listening key g should be actuated so that the springs 91 92 are against
the contacts g3 g and then if the key h is also in such a position that springs h¹ h³
are against contacts the telephone f¹ the induction coil 2 and the con-
denser fare in circuit with the exchange line and as the transmitter f* is
energised as before described conversation can take place.
The extensions C C can call station B by removing the receiver off the hook
thus forming a path for the current from the exchange battery
through their respective transmitters and actuating the visual signals
at station B. In the case of the exchange extension C the current from
the battery b flows through the contact a¹ a² the resistance a the line 1 the con-
ductor 3 the impedance coils R¹ R2 R3 R4 the conductors 5 and 9 the visual
indicator J the contacts y y² and a 2 the conductor 8 the transmitter C6 the
contact the conductor 7 the contacts a¹³ and y' y³ the conductor 10 and 6
the impedance coils R R R R the conductor 4 the contact ee³ and to ground
through the conductor 17. Should a plug be in the jack e the springe is in
contact with e and the current flows back to the grounded side of the battery b
through the line 2. The current through the visual indicator J actuates it and
gives the calling signal. To speak to the calling extension B inserts a plug Z³
into the jack and manipulates the listening keys thus establishing connection
with his telephone instrument. Should C wish to communicate with the
exchange Binserts the plug Z' into the jack e and this automatically signals the
exchange. B then disconnects the telephone instrument f from the cord circuit
by manipulating the listening key g. As long as the receiver at C is off the
hook the visual signal J2 is displayed but directly C replaces his receiver this
signal automatically is restored to its normal position. This notifies B that the
connection may be removed and when the plug Z is removed from the jack e
the exchange operator at A is automatically advised of the fact as previously
described.
In case C desired to communicate with the private extension C instead of
with the exchange, the attendant at B after ascertaining this establishes the
desired connection by means of a pair of plugs W₁ We included in the group
provided for this purpose calling the station wanted by means of the ringing
key. The signal associated with this pair of cords serves to automatically advise
the attendant at B to remove the connection when the receivers at both stations
have been replaced on the hook.
The accompanying Figure 5 shows an alternative arrangement of the apparatus at
the exchange. Line 2 after passing through the contact a³ a of the cut-off relay
and through the calling relay as being connected to an intermediate point in the
grounded battery 6 instead of to ground direct and the resistance a in line 1
is made in the form of a small incandescent lamp a³. The advantage of this
arrangement is, that should an "earth" or ground" fault occur on either line,
the exchange will be notified.
<<

page_text: It will be seen from the diagram that if line 1 be grounded lamp a³ will light
and if "ground" should occur on line 2 relay a will be energised and lamp a
lighted. Normally the current flowing through a8 is not sufficient to make the
filament bright.
Figure 5 also shows a pair of connecting cords such as are usually employed
at a central battery exchange, xl being the answering plug and the calling
plug.
The only modification necessary for the proper working of the extension line
system I have described is that the battery should be applied to one line of
the metallic circuit when the ringing key is depressed so that the supply of
current to the extension lines may not be interrupted when the exchange is ringing
up the intermediate station. For this purpose one outer contact a of the ringing
key a is connected to the battery *, the outer contact all being connected to
one side of a generator, the other side of which is put to earth.
While I have described a particular method for carrying out the improvements
it is to be understood that the scope of the invention is not to be restricted to the
specific plans described.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is:-
1. In telephone systems employing current from a central source to energise
the local transmitting and receiving apparatus, introducing a shunt of high
impedance and low ohmic resistance across the terminals of the transmitter or
the receiver substantially as described.
2. The combination of a telephone line and a ground return therefor, a battery
connected between the ground return and one line conductor, a signal connected
between the ground return and the other line conductor, a telephone at the
substation in a bridge of the line circuit, and a switch adapted to break the line
conductor containing the signal and to connect the corresponding terminal of
the telephone with the ground return, whereby current may be supplied for
exciting the transmitting telephone independently of the signal when required
substantially as described.
3. The combination of a telephone line from a central station to two sub-
stations, said line having two line conductors and an earth return, a source of
current applied to one of the line conductors between the said conductor and the
earth return, and a signal in the other line conductor between the line and the
earth return, a transmitting and a receiving telephone at each of the substations
in a bridge of the line circuit, and a switch in the line conductor containing the
signal between the central office and the first substation adapted to break the
said line conductor and connect the part thereof leading to the distant substation
with the ground return; whereby the two substations may be supplied with
current independently of the line signal, substantially as described.
4. The combination of a telephone line and an earth return therefor, a source
of current applied to one of the line conductors between the said line and the
earth return, and a line signal in the other line conductor between the line and
the earth return, a call bell in a ground branch from the line conductor con-
taining the signal at a substation, and a calling key adapted to unite the line
conductors directly while breaking the conductor containing the signal between
the said point of junction and the signal, substantially as described.
5. The combination of an extension line system leading from a central station
to two substations, a source of current connected with the line circuit at the
central office, receiving and transmitting telephones in bridges of the line
circuits at the substations, said transmitting telephones being adapted for operation
by current derived from the line, a switch in the line adapted to sever the normal
continuity of the line, and a by-path of high inductance and low resistance about
said switch, whereby the transmitters may be supplied with current while the

page_text: diversion of telephonic currents to the central office is prevented, substantially as
described.
6. The combination of a telephone line and a return circuit therefor, a source
of current connected between one line conductor and the return circuit, a signal
connected between the other line conductor and the said return circuit at the
central office, a transmitting and a receiving telephone in a bridge of the line
circuit at each of two substations, said transmitting telephones being connected
with the line to derive current therefrom, a switch or switches at the inter-
mediate substation when in one position severing both line conductors between the
telephone bridge at the same station and the central office, a permanently closed
shunt of high impedance about said switch contacts in the conductor with which
the source of current is directly connected, and a branch of high impedance
between the other line conductor and the return circuit closed by said switch in
the same position, said switch when in its other position severing the line con-
ductors between the substations, substantially as described.
7. The combination of a main telephone line having two line conductors between
a central station and a branch exchange, a grounded source of current connected
to one line, a signalling instrument connected to the other line and to the same
source of current at a different point of potential, means for connecting another
line with the said main line and means for applying a source of continuous current
to one line while transmitting a calling current over the other line.
8. The combination of two telephone circuits, two conductors uniting the said
two circuits at points of different potentials, several impedance coils in each
of the conductors, bridges between the said conductors intermediate of the repeat-
ing coils, and condensers in the bridges, substantially as described.
9. The combination of a telephone circuit, uniting two stations with trans-
mitting and receiving telephones in the circuits, a source of current in a bridge
of the telephone circuit, united extension telephone lines each with transmitting
and receiving telephones at its station, a branch from each side of the main
telephone circuit to a corresponding side of the extension line circuit, several
impedance coils in the said branch or branches, and bridges of the circuits con-
taining condensers intermediate of the impedance coils, whereby all transmitting
telephones are simultaneously supplied with current while the independence of
the telephone circuits is preserved, substantially as described.
10. The combination of a telephone line between a branch exchange and a
central office, a source of current applied to one limb of the line at the central
office, a ground return for the line, a number of extension lines in different
branches from the line conductor containing the battery at the branch exchange,
a bridge of the line circuit at the branch exchange, a telephone in the bridge,
means for closing the bridge, and an impedance coil between the said bridge of
the line circuit and the connection with the line of the extension lines, sub-
stantially as described.
11. The combination of a metallic circuit telephone line between a central station
and a branch exchange, an earth return for the line, a grounded battery con-
nected to one line conductor, and a grounded signalling instrument connected
with the other line conductor, a telephone at the branch exchange, means for
bringing it into a bridge of the line circuit, and several extension lines at the
branch exchange in ground branches from the line conductor to which the battery
is applied, said extension lines being connected in pairs for conversation, sub-
stantially as described.
12. The combination of two telephone lines between a branch exchange and a
telephone substation united in a central station, a bridge at the central station
containing a source of current, extension lines at the branch exchange connected
with the telephone line to derive current therefrom, said extension lines being
united in pairs for conversation, and electrical appliances in the branches to said
extension lines adapted to prevent the propagation through them of undulations
produced in the current in the extension lines while permitting the flow of

page_text: unvarying currents; whereby conversation may take place simultaneously in the
extension lines and in the main telephone lines by means of current derived from
the central source, substantially as described.
13. The combination of a telephone line, two line conductors between a central
station and a branch exchange, an earth return for the line, a grounded battery
applied to one line conductor and a grounded signal indicator in the other line
conductor in the central station, a bridge between the line conductors at the
branch exchange, means for closing the bridge, an extension line in a ground
branch from the line conductor to which the battery is applied at the branch
exchange, a signal in the extension line at the branch exchange, and
a telephone switch controlling the extension line for operating the
signal whereby signals may be transmitted independently through the extension
line to the branch exchange and through the main line to the central station,
substantially as described.
14. The combination of a main telephone line having two line conductors
between a central station and a branch exchange station, a grounded source of
current applied to one main line conductor and a grounded signal connected with
the other main line conductor in the central office, means for connecting another
line with the said main line and a switch actuated in making such connection
to break the normal ground connections of the line and substitute a source of
current in a bridge of the united lines, extension lines in normally grounded
branches from the main line conductor with which the battery is
nected, at the branch exchange, a telephone at the branch exchange, and switching
mechanism adapted to connect the telephone in a bridge between the conductors
of the main line, said switching mechanism being adapted to disconnect the
normal grounds of the said extension lines and to connect the extension lines in
bridges of the main circuit, substantially as described.
con-
15. The combination of a main telephone line between a central station and
a branch exchange. a source of current connected with the lines at the central
station. extension lines at the branch exchange normally connected with the said
main line, through the medium of electrical appliances adapted to impede the
passage of undulating currents through them while permitting the passage of
unvarying currents, switching apparatus for uniting the extension lines with one
another for conversation, and other switching apparatus for uniting the conductors
of the main line with those of any extension line directly, substantially as described.
16. Telephone systems and apparatus substantially as described and illustrated
in the drawings.
1000