Improvements in Party Telephone Line Systems.
Year: 1899

page_text: Date of Application, 18th May, 1899
Complete Specification Left, 17th Feb., 1900-Accepted, 21st Apr., 1900.
Improvements in Party Telephone Line Systems.
I, WILLIAM AITKEN, Engineer to National Telephone Company Limited, of
Oxford Court, Cannon Street, in the City of London, do hereby declare the nature
of this invention to be as follows:-
The object of my invention is to provide a system which will allow of one
5 pair of wires (a metallic circuit) being used by two or three firms who have
offices in two towns or districts some distance apart, to communicate between
their respective places of business with perfect secrecy, it being impossible
when is talking from his office at A to his office at B for d or e at their offices
at A or B to interrupt or overhear the conversation, and it being impossible
for e dor e to intercommunicate, the arrangement being equivalent to three
private and independent circuits between the respective places of business, with
the exception that one party only can communicate between A and B at a time,
the other instruments being locked and a signal showing that the line is engaged.
To attain this end a metallic circuit is run between one of the offices, say d in one
disfrict to one of the offices, say in the other district with branches to c and e
in one district and e¹ and c in the other. On two of the circuits-say e c
and d - fit polarised relays of suitable resistance and self induction in
bridge, the relays at e, el being of different polarity to those on d, d'. At each
station I also fit a ringing key with a battery so connected that it will actuate
the relay at the distant end of the same circuit. The third circuit e, el I bridge
at each end by a coil of suitable resistance and high self induction and differen-
tially wound (or two suitable coils) the centre points being connected through
ringing keys and polarised relays to earth. The batteries are so connected to
these ringing keys that they actuate the relay at the distant end when brought
into circuit. In each instrument I also fit a drop indicator, the coil of which is
in circuit with a battery and the local circuit of the relay. The indicator shutter
when it falls joins up a call bell and breaks the locking circuit. The shutter
is restored by a push button.
A switch in connection with the telephone rest normally connects the locking
relay (one side of which is connected to earth) through indicator contact to centre
point of relay or bridging coil. The locking relays at all stations are of opposite
polarity to those used as calling relays on the e el circuit. The locking relays
control a simple mechanical arrangement which prevents the telephone rest
rising when the telephone is lifted and prevents the ringing key being depressed.
These relays might be made to cut the necessary electrical circuits, but I prefer
he mechanical locking arrangement. When the telephone is removed from its
est the locking relay at that station is out of circuit and a battery is connected to
centre point of relays and bridging coils.
The working of the arrangement is as follows when e at A wishes to call c¹
t B:-
C presses ringing key-relay at C₁ responds dropping indicator shutter and
inging call bell. U removes the telephone from its vast and the
1

page_text: joined up actuates the locking devices at all stations except C and C¹, C¹ takes the
telephone from its rest and presses the push button to restore the indicator and
cause the bell to cease ringing. Conversation can then be carried on between C
&C. Placing the telephones on the rests restores all to the normal.
This system is also perfectly applicable to working in connection with a tele-
phone exchange system.
Improvements in rarty Telephone Line systems.
1, WILLIAM AITKEN, Engineer to The National Telephone Company Limited, of
Oxford Court, Cannon Street, in the City of London, do hereby declare the nature
of this invention and in what manner the same is to be performed, to be particu-
larly described and ascertained in and by the following statement;-
The object of my invention is to provide a system which will allow of one
pair of wires (a metallic circuit) being used by two or more firms who have
offices in two towns or districts some distance apart, to communicate between their
respective places of business with perfect secrecy. Taking as an illustration
three firms on one party line as on Fig. 1 the apparatus is so arranged that it
is impossible when U is talking from his office at A to his office at B for D or E
at their offices at A or B to interrupt or overhear the conversation, it being also
impossible for C, D) or E to inter-communicate, the arrangement being equivalent
to private and independent circuits between the respective places of business,
with the exception that one party only can communicate between A and B at a
time and when so doing the other instruments are locked, and a signal shews at
the disengaged stations that the line is engaged. To attain this end a metallic
circuit is run between one of the offices, say D in one district to one of the offices,
say D in the other district with branches to C and E in one district and C and E
in the other. On two of the circuits-say C, C and D, D'I fit polarised
relays e, el, e, et, of suitable resistance and self induction in bridge, the relays
at C, being of different polarity to those on D, D¹. At each station I also fit
a ringing key e, e', e, e, with a battery d, d¹, d³, d, so connected that it will
actuate the corresponding relay at the distant end of the same circuit. The third
circuit E, E, I bridge at each end by a coil t, 2 of suitable resistance, high self
induction, and differentially wound (or two suitable coils) the centre points
being connected through ringing keys, e, and polarised relays, to earth.
The batteries ; d, are so connected to these ringing keys, , that they
actuate the corresponding relay at the distant end when brought, into circuit.
In each instrument I also fit a drop indicator f, f', f², f³, f, f³, the coil of which
is in circuit with a battery do, do, d³, d³, dw, d, and the local circuit of the
relay e, e, e, e, e¹, e. The indicator shutter i,,,,,, when it falls causes
spring, g³, g, g, to close a circuit which joins up a call bell k, k, l,
,,, and the shutter falling also carries spring h, h, 2, 13, 14, 1,
away from
- a contact which breaks the locking circuit 7, of the instrument called. The
shutter is restored by a push button j, j, P³, 1, P.
A switch p, p, p, in connection with the telephone rest 1, 1, 1º,
13, 14, 1, normally connects the locking relay 4, 1', q², 1', q', q (one side of which
is connected to earth) through indicator spring,,, h³, ha, h³, to centre
point,,,,, of relay e, e¹, e³, et, or, bridging coil t, 2. The locking
relays, 1, 9, 1³, q', q³ at all stations are of opposite polarity to those used as

page_text: These
calling relays e, on the E. E circuit. The locking relays T T', P², T', T; Pr
control a simple mechanical arrangement u, u, ², ³ (see detail drawing) which
prevents the telephone rest rising when the telephone n, n', n², n³, n', n², is lifted,
and prevents the ringing key c, c, c², c³, c, c, being, depressed..
relays 'q, q, q, q, q might be made to cut the necessary electrical circuits, but
I prefer the mechanical locking arrangement. When either of the tele-
phones n,, n², n³, n, n³ is removed from its rest 1, 1, 1, 1, 4, the locking
relay at that station is out of circuit and a battery 12, 13, 14, ds, d¹, or d¹, is
connected to the centre point of relays c, e, e³, et, or bridging coils t', ²..
The working of the arrangement is as follows when Cat A wishes to call C¹
at B:--
to
C momentarily presses ringing key thereby connecting battery d to lines a, b,
the circuit then being over one line to a, a, a, and through coils of relay and
back to battery d by line 63, 64, b, and b (there are also circuits through
relays e, c, but as these are oppositely polarised they do not respond) the local
circuit of relay is closed and the circuit of battery, and coil of indicator f³
completed and shutter is released, and falls completing circuit of bell through
battery, and the bell therefore rings. The shutter also causes spring
break contact with centre point and locking relay 3 is cut out of circuit. C
takes telephone n³ off rest and by plunger restores shutter and stops ring-
ing, and restores indicator circuit to normal condition. After depressing-ringing
key c, C also takes telephone from rest . This connects earthed battery d
through springh, and contact to centre point of relay e through both coils in
parallel, and over a and b wires in parallel through coils of relays el, and e', and
two windings of bridging coils, and in parallel to centre points and through
springs P, P, P², p³, P, and locking relays q', 7, 7, 7, actuating them so
so that the springs operated by the telephone rest and ringing keys are locked
and these subscribers cannot interfere with the speaking circuit. When C
replies the locking current is supplemented by battery D, DE, E¹, remain
locked out while C, C are talking, and when the telephones, ¹, are returned
to their rests they are released.
The circuit in the case of E calling E is slightly different as when the ringing
key is depressed an earthed battery is connected through the two windings
of coil tin parallel and over wires a², b², a', b², a², b², a³, b³, through two windings
of coil through ringing key, through coils of relay to earth. There is also
a circuit from battery at the same time through all locking relays 4, 1', T³, T'
but as they are oppositely polarised they do not respond.
is
Fig. 2 shews somewhat more in detail the locking device which prevents a non
engaged station interfering with an engaged one represents the telephone rest
on switch hook, a ringing key, the electro-magnet controlling the locking
device, u u, u²; ³, and engaged signal e. The action being that when coil
energised, arms, are pulled over so that the end of
prevents it rising when the telephone. is lifted from rest
under spring so that it cannot be depressed by plunger
engaged shutter is moved to v¹.
and
is over spring
and the end of ² is.
at the same time the "
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. Two or more independent and secret telephone circuits on one pair of line
wires substantially as described.
2. The arrangement of keys, circuits, relays and other appliances substantially
as described whereby on a pair of line wires between two districts, two or more
instruments are arranged in such a manner that one instrument in one district
can communicate only with the coresponding instrument in the other district, the
act of taking the telephone off the switch lever at the calling instrument locking
all the instruments on the line wires (with the exception of the instrument with

page_text: which the calling instrument is arranged to communicate) rendering it impossible
for any overhearing or interference with the communication taking place, the
act of replacing the calling telephone and called telephone on their respective
switch-levers unlocking all the instruments on the line wires, thus restoring them to
their normal positions for giving or receiving a call.
Dated this 17th day of March 1900