Improvements in Telegraphic and Telephonic Apparatus.
Year: 1894

page_text: Date of Application, 6th Apr., 1894
Complete Specification Left, 5th Jan., 1895-Accepted, 9th Feb., 1895
PROVISIONAL SPECIFICATION.
[Communicated from abroad by LA SOCIÉTÉ ANONYME POUR LA TRANSMISSION
DE LA FORCE PAR L'ELECTRICITÉ, of 13, Rue Lafayette, Paris, France.]
Improvements in Telegraphic and Telephonic Apparatus.
I, JOHN IMRAY, of No. 28 Southampton Buildinge, Chancery Lane, in the
County of London, Consulting Engineer and Chartered Patent Agent, do hereby
declare the nature of this invention to be as follows:-
This invention relates to telegraphic and telephonic apparatus so constructed and
arranged that the receivers at a station select and separate only those signals
which are specially addressed to them without being acted on by any other signals
that are at the same time transmitted along the line. For this purpose, transmitting
instruments are provided to send along a line electric undulations of various periods,
each instrument determining a particular frequency of undulation. This is
conveniently effected by employing an instrument like a tuning fork which is put in
vibration and maintained in vibration by an electro magnet excited by a local
battery, and which has between its limbs a magnetic core having a coil which
having corresponding undulations induced in it transmits these along the line to a
Each of these receiving
suitable receiving instrument at a distant station.
instruments consists of a self induction coil combined with a condenser constituting
a resonator which responds to electric undulations of certain frequency and to none
others.
A number of these transmitters and receivers being connected to a line, operate
each for its own undulation period, the receivers translating the signals sent by the
transmitters by working telegraphic instruments or acting on the microphones of
telephonic receivers.
Thus a single line
made to serve for the transmission and reception of signals
for a number of different stations, each station having a number of transmitters
timed to different periods of undulation, and a number of receivers correspondingly
timed, and thus a number of different signals may be transmitted by the line
simultaneously from the various stations to the various stations without interfering
with one another.
Dated this 6th day of April 1894.
ABEL & IMRAY,
Agents for the Applicant.
Improvements in Telegraphic and Telephonic Apparatus.
I, JOHN IMRAY, of No. 28 Southampton Buildings, Chancery Lane, in the
County of Loudon, Consulting Engineer and Chartered Patent Agent, 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 :-
This invention relates to telegraphic and telephonic apparatus so constructed and
arranged that the receivers at a station select and separate only those signals which
are specially addressed to them without being acted on by any other signals that

page_text: are at the same time transmitted along the line. For this purpose, transmitting
instruments are provided to send along a line electric undulations of various periods,
each instrument determining a particular frequency of undulation.
Such an instrument may be constituted by connecting in series or in parallel a
self induction coil and a condenser.
Fig. 1 shews such a connection in series. If R denotes the resistance of the system,
L the co-efficient of self induction of the coil, C the capacity of the condenser,
E, an external alternating electro-motive force developed between the terminals P₁P,,
also ✓ the frequency of the variations of this force, then the intensity I of the
alternating current traversing the system is given by the known formula.
then the intensity I would vary also, its values in relation to those of the frequency
may be represented by a curve such as that in Fig. 2, which passes through a
E
1
=
1
R corresponding to the abscissa T 2π √ CL
1
It
maximum ordinate I =
rises and descends very rapidly on each side of the maximum ordinate. Hence, if
the electro-motive force E, is the sum of several forces of different frequencies T
1 the corresponding terms of frequency comprised in the expression
of the intensity I will be far from proportional to the amplitudes of those which
enter the expression for the electro-motive force.
1
T
Tn'
1
Practically it may be arranged that no appreciable currents shall enter the
sounder except those which have frequencies differing from the value 2TT CL
only by a quantity which may be as small as desired.
Fig. 3 shews an arrangement of self induction coils S and condensers C connected
to each, all the wires from the coils S connected together to one end of a line L
leading to earth T, whilst the wires from the condensers C pass by signalling
instruments E to earth. The coil S, and condenser C, are such that their line
1
allows passage of only such waves as have the frequency and so with the others;
T₁"
and thus there may be any number of circuits connected to the line L each of which
can be traversed only by currents of certain frequency.
Fig. 4 illustrates a wave selecting instrument according to this invention.
A vertical bar consisting of superposed and insulated thin plates constitutes the
core of a number of coils S, S₁-S₁, each having its number of convolutions inversely
proportional to the frequency of the currents traversing it. At the sides of a bare
two combs A. B, C D made of superposed and insulated thin plates, with their teeth
projecting between the coils; thus the flux caused by each coil can close upon itself
through the teeth which embrace the coil, without interfering with the other coils.
The armature thus constituted rests on a base containing condensers C1 C2-C10; the
entering wires of the coils are connected to the posts M₁ M,-M10, and then leaving
wires to the condensers C, C2-C10 respectively, the condensers themselves being
connected to the posts N, N₂-N10 If indicates the permeability of the magnetic
circuit of a coil, this depending on the thickness of the small intervals between the
ends of the teeth and the edge of the core, will be nearly constant for all the coils.
If N indicates the numbers of convolutions, say of the strongest coil, its co-efficient
of self induction Li = 4 p N. As has already been shewn, the sounder

page_text: 1
comprising the strongest coil can only be traversed by currents of frequency T₁
when T₁ = 2 CL, and since L₁ = 4 p N², T₁ = N √ 8³p C. The other
sounders will be traversed by currents of frequencies
&c., and thus, if there
T T
were n sets of self induction coils and condensers, these would give passage to
currents of n different frequencies.
In applying the principles set forth to telegraphy, the signalling apparatus E
of Fig. 3 may be Morse instruments for instance, pieces of iron subdivided so as to
be excited by alternating currents being substituted for the massive cores and
armatures. The coils S, &c. and condensers C, &c. of Fig. 3 may be supposed to
be grouped as in Fig. 4, the whole constituting a station apparatus such as is shewn
in Fig. 5. If this station be connected to 3 others, 4 sounders will be required, as
will hereafter be shewn. In Fig. 5, A and B are respectively Morse receiver and
transmitter, C the wave selector having 4 sounders, I. the main line connecting
stations. are two small transformers which are not essential, but are useful
for allowing the employment of high tension currents to operate for great distances
without requiring relays. Their primary circuits p communicate with the line at X
and with earth T. As the introduction of a transformer in a circuit does not affect
self induction or capacity, the secondary circuits are connected as follows.
for the entering
The entering wires of transformer is connected to the post m₁,
wire of one of the sounders of C, the leaving wire of this sounder is connected to n₁
the post of the entering wire a of the receiver A, the leaving wire of which is
$1 of the
connected to the leaving wire of the transformer Z. The entering wire.
transformer is connected to the posts m₂ m, m₁ of the other sounders of C. The
transmitter B can be connected by the switch F to any one of the posts n₂ ng n₁ for
the leaving wires of the sounders. The connections being thus arranged similarly
at separate stations, they can communicate by a single line Las indicated in Fig. 6,
in which a ẞy 8 indicate separate stations. In the line there is introduced a
transformer or several of these as may be determined by the condition that there
should be one on that part of the line which is the shortest connection of any two
stations; in the present case three are shewn, which are all alike, each comprising
a secondary circuit in the line, and as many primary circuits as there are sounders
at each station, in this case four. Each of these primary circuits connect to the
terminals a₁ b₁ a, b, &c. of four alternators supplied with currents of different
frequencies, say for instance, 10,000 for circuit 1,20,000 for 2, 30,000 for 3, and
40,000 for 4. The four sets of apparatus at the stations are tuned to these
frequencies, so that each sounder passes only currents of one frequency. Let the
a for 10,000,
ẞ, Y, and be arranged each for one of these frequencies,
ẞ for 20,000 &c., that is to say its receiver is in each case connected to that
particular sounder. If now has to communicate with 8, then by means of the
switch at connection is made to the sounder for 40,000 which is 8's number.
Consequently the stations ẞ and 8, and they only can communicate, all the other
stations being left free to communicate amongst each other.
stations
a,
Instead of Morse apparatus which have been mentioned by way of example,
other receivers may obviously be employed, and these may be different at different
stations, the selection of the wave currents being independent of the character of
the receiver, which however must have their electro magnets suited for alternating
currents.
For applying the invention to telephony, according to one method, the receivers
and transmitters A and B are telephonic. Currents can still be sent into line
having different frequencies, each of which will pass between two suitably related
stations, missing all others. On speaking to one of the transmitters the variations
of resistance cause beats or variations in the intensity of the alternating current,
and these are perceived by the appropriate receiver. It is well known that, when
such beats recur very rapidly, they are not perceived as separate, but they form a

page_text: "tone of pitch determined by the number of beats per second. When the primary
tone is very high, it ceases to be perceived by the ear, whilst its beats nevertheless
continue to be audible. Thus it is possible to employ alternators producing
currents transmitted telephonically and tones of pitch so high that the tones
themselves are not heard, but only the beats resulting from variations of resistance
caused in the telephone transmitter, these beats reproducing speech. This method
demands the production of as many electromotive forces of different but very high
frequencies as there are to be separate communications. The production of such
currents may be effected in many different ways, as for instance by the following
method. As the energy required is comparatively small, tuning forks highly
magnetised may be electrically maintained in vibration, inducing currents in coils
placed between their prongs, as shewn in Fig. 7 which represents the installation
at a central station communicating by a single line to other stations with which
three separate conversations may be simultaneously carried on. On a base S are
mounted 3 tuning forks A, B, C having different vibrations such, for instance,
as 20,000, 15,000 and 10,000. To maintain their vibration, electromagnets a, b, c
having their coils connected to a local battery are placed beside them. Each of
the circuits being closed by a carbon contact x, y, z and through the fork itself,
the variations of resistance due to the variations of pressure on the carbon determine
synchronous variations of the attraction of the electro magnet connected to the
fork which is thus constantly kept in vibration. The coils m n p or soft iron cores
interposed between the prongs, having induced in them currents corresponding to
the vibrators, are connected in parallel between two points of the line connecting
the two central stations, but as they have co-efficients of self induction which would
uselessly increase resistance, condensers of capacities C₁ C, C, are introduced in
the connections to counterbalance the effects of self induction which may be taken as
quadrants and the capacities C, C₂ C, in farads. In order to select the currents,
the selector TT, consisting of 3 electric sounders comprising self induction coils
having co-efficients L₁ L, L, and condensers having capacities T₁ T, T₂ these
being arranged so that
2T LITH
2π √ LT.
3
1
==
20,000
l
=2√√LT
15,000
3
1
1
10,000
The condensers may be of any known construction. The self induction coils
being for very weak currents, may have iron cores almost closed, which will always
be far from saturation, and have great permeability; the coils may therefore he
small. The sounders are connected to the posts P, Q. R, of which the post P is
connected to the telephone receiver, and Q, R are connected by switch to the trans-
mitter, both of which instruments may be such as are usually employed. Thus
according to the system described:
1. Ordinary telephones supplied with currents of great frequency give perception
of only the sounds resulting from the succession of beats caused by variations of
intensity of the currents.
2. Currents of great frequency traversing an ordinary telephonic apparatus induce
currents of the same frequency in its microphone through the small transformer
which always accompanies it, as the same effects resulting from variations of
resistance in the secondary circuit of the transformer as from variations in its
primary, the variations produced by speaking to the microphone in the secondary
circuit, determine variations or beats in the primary circuit of the stations, which
reproduce speech.
The microphone battery behaves simply as an additional resistance, the influence
of which may be neglected, for the variations of intensity of the current furnished

page_text: by it cannot develop induction currents, as these could not traverse sounders having
no corresponding frequency. Thus nothing has to be changed in the telephonic
In
instruments or their connections among themselves and the central office.
connecting from one central office to another, arrangements have to be made for
calling.
For this purpose in connection with the sounders are arranged solenoids o₁ σ2 z
containing moveable iron cores k₁ k₂ ka which by suitable connections cause
signals vv, vs to appear or disappear. Each solenoid is provided with a double
interrupter. When it is inserted for instance in f₁, the leaving wire of the solenoid σ₁
is connected to earth, the post P and the corresponding post at the other station
being connected to nothing. The current of great frequency capable of traversing
each of the correlated sounders is then closed on itself through earth, keeping
hidden the signal ₁ and that corresponding at the other station. If for instance
the office desires to use the sounder L, T₂ the operator at intervals breaks and
makes contact for the solenoid og to earth by inserting and withdrawing the plug in f...
Thus the currents traversing the solenoids of the correlated sounders at the two
stations is at intervals interrupted, and the signals appear and disappear. When
the signal is perceived the operator at the other station removes the corresponding
plug and inserts it in the hole , corresponding to f2. As the two signals remain
visible whether the plug is in f2 or not, the operator at the first station knows that
his call has been received, and putting his plug in 2 communicates with the other
station. On ending the conversation, the plugs are put in f₂.
In the installation shewn in Fig. 7 are shewn the tuning forks and condensers
which are employed only in one of the connected stations.
The method above described is characterised by the provision of as many currents
of different frequencies as are required for so many simultaneous conversations, each
station being capable of varying the intensity of any of the currents, but of being
influenced only by one.
According to another method of operating, no source of electromotive force
independent of the telephonic instruments is required, and instead of reproducing
speech by beats of a special current, it is effected by currents of different frequencies
produced in the different telephone transmitters, these being suitably selected by
electric sounders. Suppose for instance 4 stations a ẞy & Fig. 8 connected by one
line L had to communicate simultaneously, in each station are arranged 4 wave
selectors CC, C, C, each comprising 10 sounders as in Fig. 4. Let the 10 sounders
of C at a be such as allow passage of currents of frequencies, 100, 200 or 1000
The sounders of C₁ are
respectively they are connected parallel as in Fig. 8.
suited for frequencies 105, 210-1050; those of C, for 110, 220-1100, those of C*
for 115, 230-1150. The self induction coils and condensers are to be such that an
electromotive force say of frequency 105, capable of causing a current of intensity I
in one of the sounders, can only cause currents of intensity = (where n may be any
I
n
number however great) in the two sounders suited for frequencies next to 105. As
previously arranged for telegraphy, the stations have certain frequencies attributed
to them, say
100, 200-1000 for station a
105, 210-1050
"
وو
110, 220-1100
"
"
115, 230-1150
وو
"
В
At each station the receiver A is connected to the wave selector corresponding
to the frequency attributed to the station, and the transmitter B is connected through
switch F to one or other of the remaining 3 wave selectors.
If a current, say of frequency 105, is sent into line it can traverse only the
receiver suited for that frequency, that is to say the receiver at B. A current of
this frequency can be sent from any of the stations on connecting, by the switch F

page_text: only a limited number of the telephone vibrations are thus transmitted, speech is
nevertheless transmitted for
1° Any succession of phases may be considered as the superposition of a very
great number of harmonies of a very low fundamental pitch, these having very
small successive intervals.
2° In order that conversation may be intelligible, it is not necessary to transmit
all these harmonies, those only which correspond to one fundamental tone being
sufficient, just as the design of a painting can be seen by looking through a glass
which allows only one colour to pass.
Y
Thus the two
Besides the main stations a ẞy & there may be secondary stations with which
communications have to be made. Let there be 3 such stations a a₁ to a₁, each of
these wires connected to a switch F F F &c. by which they can be connected on
the one hand with the wave collector tuned to the frequency for the central station
on which the secondary depends, and on the other hand with the wave selector
tuned to the frequency for the station from which communication is sent. Suppose,
for instance, the secondary a of the main station a has to be connected to a of
station the station a connects its transmitter to the wave selector C, tuned to the
frequencies 110, 220 &c. which belong to y, and can thus call y to put in commu-
nication with a, placing the switch of a on the contact for C₂. Station then
places the switch of a, on the contact for C which belongs to a.
stations a and a, are connected by a line by which can only pass, to the exclusion
of all others currents of frequency 100, 200 &c., and 110, 220 &c., the other stations
being left free to communicate. As all the subscribers' instruments remain
unchanged, it is only necessary to consider how one central station can call another.
For this purpose in each of the derived circuits comprising a wave selector Tras
in Fig. 9 is introduced a solenoid σ, the core of which in moving in the direction of
the arrow presents a signal v. In the same circuit is introduced a magnetic call
with vibrating steel blade, carrying a coil r. By pressing on t it is made to vibrate
between the permanent magnets on each side. A spring k bearing on the blade
short circuits the coil when it is at rest as may be understood from Fig. 9. The
length of the blade is so adjusted that its period of vibration coincides with that of
the currents which have to traverse one of the coils of the sounder. Thus the
currents induced in by its vibration between the magnets can traverse the
sounder and actuate the solenoid, and the signals of the two stations are exhibited ;
when once seen the operators cause them again to disappear.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
:-
1. A wave selecting instrument consisting of self-induction coils combined with
condensers of suitable capacities, so that the elementary circuits or sounders thus
formed can be traversed only by alternating electric currents of the frequencies
determined by the coils and condensers.
2. The combination at several stations on one line, of ware selecting instruments
and instruments producing alternating electric currents of different frequencies,
suited to the coils and condensers of the wave selectors, with telegraphic transmitters
and receivers arranged and operating substantially as described.
3. The combination at several stations on one line of wave selecting instruments
and instruments producing alternating electric currents of different frequencies
with telephonic transmitters and receivers arranged and operating substantially
as described.
Dated this 5th day of January 1895.
ABEL & IMRAY,
Agents for the Applicant.