Improvements in Intercommunication Telephone Systems.
Year: 1899

page_text: PROVISIONAL SPECIFICATION.
Improvements in Intercommunication Telephone Systems.
I, LANCELOT EDWARD WILSON, of No. 15, St. Clements Mansions, Lillie Road,
Fulham, in the County of London, Electrician, do hereby declare the nature of
this invention to be as follows:-
In the telephone system known as
intercommunication," a number of stations
are so connected that any one of these can communicate direct with another of
them instead of having to connect through a central exchange.
The chief objection to this system is that, at any of the stations, communications
can be heard by placing their telephone in circuit.
The nearest approach to a system of private intercommunication is effected by
means of "break jacks," but this requires special wiring and is therefore expensive
and also cumbersome; although, according to this system, an attempt to overhear
at one station results in all stations beyond it being cut off, the station that
intercepts would still be connected to the transmitting telephone, so that the
intercommunication cannot properly be termed private.
The present invention relates to a system whereby, when any two of a number
of stations are in communication with each other, they cannot be overheard by the
other stations, the telephones of these being rendered ineffective until the circuit
of the two is disengaged.
For this purpose, I provide at each of the intercommunicating stations, besides
the ordinary telephone appliances including battery, transmitter, receiver and
induction coil, a small electromagnet, the armature of which, when the magnet is
inert, makes a contact by which the secondary coil is short circuited on itself, the
receiver being thus rendered ineffective.
At each station also there are as many calling keys as there are other stations
in the group, and an answering key, all these keys being arranged to make the
necessary contacts for operating in the following manner.
Assuming that there are 4 intercommunicating stations A, B, C, D, and that A
calls Cintroducing his battery into the line. C in answering does not introduce
his battery but the current from A's battery energises both his and C's electro-
magnets which attracting their armatures break the contacts for the short circuits
of the secondary coils and so bring their receiving instruments into circuit. Mean-
while at the other stations B and D there can be no listening because there is no
circuit unless they use their calling keys by which they bring their batteries into
line thus opposing the current already in the line which would otherwise open
the short circuit of their secondary coils. As the opposing currents are in each
case equal or nearly so, the electromagnets at B and D remain inert and conse-
quently the secondary coils there are short circuited on themselves and the receiv-
ing instruments are ineffective. B and D however may communicate with each
other in the same way as A and C are communicating.
Dated this 2nd day of December 1899.
ABEL & IMKAY,
Agents for the Applicant.

page_text: Improvements in Intercommunication Telephone Systems.
I, LANCELOT EDWARD WILSON, of No. 15, St. Clements Mansions, Lillie Road,
Fulbam, in the County of London, Electrician, do hereby declare the nature of
this invention, and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
66
In the telephone system known as intercommunication," a number of stations
are so connected that any one of these can communicate direct with another of
them instead of having to connect through a central exchange.
The chief objection to this system is that, at any of the stations, communications
can be heard by placing their telephone in circuit.
The nearest approach to a system of private intercommunication is effected
by means of "break jacks," but this requires special wiring and is therefore
expensive and also cumbersome. Although, according to this system, an attempt
to overhear at one station results in all stations beyond it being cut off, the station
that intercepts would still be connected to the transmitting telephone, so that the
intercommunication cannot properly be termed private.
The present invention relates to a system whereby, when any two of a number of
stations are in communication with each other, they cannot be overheard by the
other stations, the telephones of these being rendered ineffective until the circuit
of the two is disengaged.
For this purpose, I provide at each of the intercommunicating stations, besides
the ordinary telephone appliances including battery, transmitter, receiver and
induction coil, a small electromagnet, the armature of which, when the magnet is
inert, makes a contact by which the secondary coil is short circuited on itself,
the receiver being thus rendered ineffective.
All stations are connected to each other by a line from each, branching to all
the other stations, in the usual manner.
At each station also there are as many calling keys or jacks as there are other
stations in the group, and an answering key or jack, all these keys or jacks being
arranged to make the necessary contacts for operating as I shall describe referring
to the accompanying diagram which shows a station B in communication with a
station A and an intermediate station C which can under these circumstances
have no communication with A, that station being already engaged by B.
At each station besides the usual appliances, battery b, transmitter t, receiver r,
primary and secondary s of the induction coil, there is arranged, according to
my invention, small electromagnet m, having an armature operating spring
contacts c. Also in the lines I introduce certain resistances x. It will be seen
that when the magnet m is inert as at C station the lower contact at c is broken
but the upper contact is made, the secondary coil s being thus short circuited on
itself. Assuming that B calls A introducing his battery into the line and so
energising both his own and A's magnet m. Their armatures being attracted
break the upper and make the lower contacts at c thus breaking the short circuits
of their secondary coils and enabling them to communicate. Should C attempt
to communicate with A or B by calling and so bringing his battery into line,
the current from C would oppose the current already in the line and consequently
could not energise C's magnet m, and therefore could not open the short circuit
of his secondary coil. In like manner the secondary coil of any other station
would remain inert preventing his receiver from operating. C, however could
nevertheless communicate with another station D in the same way as B com-
municates with A.

page_text: 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:
-
In combination with the usual telephonic appliances and connections at each
intercommunicating station, an electro magnet, its armature, spring contacts
worked thereby and a short circuit including the secondary of the induction coil,
substantially as and for the purpose set forth.
Dated this 27th day of August 1900.
ABEL & IMRAY,
Agents for the Applicant.