Improvements in Electrical Transmission of Energy for Telegraphic Signalling.
Year: 1895

page_text: Date of Application, 9th July, 1895-Accepted, 14th Sept., 1895
COMPLETE SPECIFICATION.
Improvements in Electrical Transmission of Energy for Telegraphic
Signalling.
I, MICHAEL IDVORSKY PUPIN, of No. 46 West 72nd Street, in the City of
New York, in the County of New York, and State of New York, 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:-
First When several alternating simple harmonic electromotive forces of
different frequencies are impressed upon an clectrical line conductor each electro-
motive force will produce in that conductor the same current as if the other
electromotive forces were not present. The current resulting from the simultaneous
action of all these electromotive forces will, therefore, be a complex harmonic
current. Such a current can be analyzed by means of clectrical resonators in just
the same way as a complex harmonic sound can be analyzed by means of acoustical
resonators.
Second: When a condenser is inserted in a circuit carrying a simple harmonic
current and the condenser is then shunted by means of a coil of adjustable self-
induction and of low resistance but containing little or preferably no iron then the
current in this shunt circuit can be made many times as strong as the line circuit
by adjusting the condenser capacity and the self-induction of the shunt circuit
in such a way as to make the shunt circuit resonant to the current of the main
circuit.
Third: When an alternating electromotive force is impressed upon the primary
of an induction coil then under ordinary conditions the electromotive force
induced in the secondary will not be greater than the product of the primary
impressed electromotive force multiplied by the ratio of the secondary to the
primary turns. If, however, the primary current be increased by electrical
resonance produced by the reaction of a condenser upon the primary circuit
then the secondary electromotive force can be made many times as large as the
product just mentioned. These physical facts have been investigated by me very
carefully in the course of my perfecting the following invention.
The explanation of my invention will be understood most clearly if I divide it
into two parts and explain each part separately.
FIRST PART OF THE INVENTION.
Consider a line conductor, say a long telegraph line X Y as represented in the
electrical diagrams of Figures 1, 2, 3, and 4. Considering first the diagram of
Fig. 1, let us suppose that a certain number of electromotive forces of different
frequencies are impressed upon the conductor X Y. For the sake of simplicity
I shall consider only two such electromotive forces. A and B are alternators
producing these electromotive forces; they are connected to the primary circuits
of induction coils C E and D F. The secondary circuits of these coils form a part
of the line conductor which is grounded at g and gl. Let the impressed electro-
motive force furnished by A have a frequency of say 250 periods per second and
let that furnished by B have a frequency of 350 periods per second. At the
distant and of 1.
1
IT

page_text: current coming over the line will divide among these two branches according to
the inverse ratio of their impedance. Hence if in one branch the capacity of the
condenser H and the self-induction of the coil K are adjusted in such a way as to
reduce the impedance in that line to the ohmic resistance for the frequency of
250 periods per second then most of the current induced in the line by the
alternator A will pass through the branch H K and only a small fraction of this
current will pass through the other branch. The branch H K is then in resonance
with the current induced by the generator A.
Similarly if the electromagnetic constants of the branch I L are adjusted in
such a way as to render IL resonant to the current induced in the line by the
alternator B then most of this current will pass through this branch and only a
small fraction of it will pass through the other branch H K. These two branches
are, therefore, selective with respect to those currents to which they are resonant.
If both alternators act simultaneously on the line X Y then most of the current
induced by A will pass through the branch H K and most of that induced by B
will pass through the branch IL.
In Fig. 2 the arrangement of circuits is similar to that in Fig. 1 except that the
selective circuits K M H, and L O 1 are placed in inductive relation to the liue
conductor. These selective circuits have each auxiliary coils K and L of
adjustable self-induction and condensers H and I of adjustable capacity respec-
tively. Consider now the circuit H M K. If the self induction of its coils K
and M and the capacity of its condenser H is adjusted in such a way as to
make that circuit resonant to the frequency of the current induced on the line
by the alternator A then this current will in this circuit be very much larger
than that induced by the same line current in the other circuit OL I. The
circuit M K H is therefore selective with respect to the frequency of the
alternator A. Similarly the circuit OL I is made selective with respect to
the frequency of the alternator B.
In Fig. 3 the selective circuits are shunted with the line by means of the
condensers H and I. The selective circuits have self-induction coils which are
denoted in the figure by the letters K and L. In that case also the selectiveness
of any one of the circuits, say the circuit H K is effected by adjusting the self-
induction of the coil K and the capacity of the condenser H in such a way as to
render that circuit resonant to one of the alternating currents of the line.
In Fig. 4 the arrangement is the same as in Fig. 3 except that for the purpose
of better adjustment additional condeusers M and N are placed in the selective
circuit and in series with the line condensers H and I.
The selectiveness of the receiving circuits can be increased by a disposition of
circuits given in Fig. 5. This disposition of the receiving circuits differs from
that in Fig. 4 in so far only that the receiving shunt circuits HKM and IL N
are made to act inductively each upon auxiliary secondary circuits U V W
and RST. In each of these secondary circuits there is a coil denoted by V and S
respectively, of adjustable self-induction and a condenser denoted by W and T of
adjustable capacity, by means of these coils and condensers each shunt circuit
like H M K with its auxiliary secondary circuit U V W is made resonant to a
particular frequency coming over the line. There are many other ways in which
selective circuits may be attached to the line but the ultimate object in view in
each will be to adjust the self-induction and the electrostatic capacity of a circuit
in such a way as to render its impedance a minimum to an electromotive force of
a given frequency.
I prefer the arrangement given in Fig. 3, Fig. 4 and Fig. 5, for two reasons:
First The resonance current in the selective shunt circuit can be made very
much larger than the line current.
Secondly: The various resonant shunt circuits interfere with each other much
less than in any other arrangement.
I shall now describe briefly how such a line current with selective circuits at the
receiving end can be used for multiple telegraphy.

page_text: Reference is now made to the diagram in Fig. 6. The disposition of the various
circuits represented in this diagram differs from that of Fig. 4 in two particulars
only. First; keys j and jare inserted in each alternator circuit by means of
which these circuits can be made and broken. Secondly; each selective receiving
shunt circuit contains a low resistance telegraph sounder, p and q respectively.
These sounders should contain a small quantity only of very finely laminated iron
for their cores. It is evident that having adjusted the self-induction and the
capacity of the receiving shunt circuits 1 and 2 in such a way as to render them
resonant to the frequency of alternators A and B respectively then whenever keyj
will
is depressed and the circuit of A closed the sounder p will act, and sounder
not be affected, and in the same way when the key is depressed then sounder q
will act, whereas sounder p will not be affected. If both keys are periodically
opened and closed simultaneously or in any manner whatever, then each sounder
will respond to the signals of its own key and practically just the same as if the
other key were not acting at all.
It is clear that in this manner a large number of independent telegraphic
messages can be sent simultaneously over the same line conductor, and that this
method of electrical signaling constitutes a new method of multiple telegraphy.
All that is necessary is a large number of alternating currents of different
frequencies at the transmitting end of the line and a corresponding number of
selective receiving circuits, each circuit being made resonant to one of the
alternating currents impressed upon the line at its sending end.
Experience has taught me, however, that the invention so far disclosed operates
imperfectly, especially when applied to long telegraph lines. I have investigated
carefully these defects and have succeeded in eliminating them. I shall first state
their nature and shall describe then the means by which I succeeded in removing
TL
The system of multiple telegraphy represented in Fig. 6 labors under two
difficulties which prevent its completely successful operativeness, especially when
it is required to send a large number of messages simultaneously over a long line.
These difficulties are:
First say it is required to send eight messages simultaneously over a long line.
It is evident that we shall have to employ eight transformers like C E, one for
each transmitting station and eight condensers like H, one for each receiving station.
These coils and condensers give the line a very large impedance so that it becomes
necessary to impress a high voltage current upon the line in order to produce a
sufficiently strong current in the receiving branches. A simple consideration will
show that employing ordinary means of transformation this task becomes
exceedingly difficult. For if we employ a low voltage alternator then the number
of turns in the secondary or line coil of the transformer E must be made large
which increases the impedance of the line. If on the other hand we employ a high
voltage alternator then the sparking of the key becomes very serious and almost
completely unmanageable. This is the first serious difficulty which will be met in
the method of multiple telegraphy so far disclosed.
Secondly The second serious difficulty is this: it is impossible to produce by
ordinary apparatus a simple harmonic electromotive force. Ordinary alternators
produce an alternating electromotive force in which in addition to the fundamental
frequency there are upper harmonics whose frequency is an odd multiple of the
fundamental frequency. The harmonics of three and five times the frequency of
the fundamental are especially strong. But if in multiple telegraphy any one
sending station sends a complex harmonic electromotive force then one of its upper
harmonics is liable to correspond to the frequency of some other sending station
and hence confusion will follow. To avoid this confusion, it is necessary to suppress
all the upper harmonics and impress the fundamental frequency only upon the line.

page_text: I have succeeded in accomplishing this and at the same time overcome the first
difficulty described above.
The means employed will be explained by a reference to diagram of Fig. 7.
A is an ordinary alternator. CD is an induction coil preferably containing no
iron. E F is another induction coil without iron. Its secondary F forms a part of
the line XY. The primary C of the first induction coil C D is connected to the
alternator; the secondary D of this induction coil and the primary E of the second
induction coil E F form one circuit. A condenser G is inserted in this circuit.
Its capacity is adjusted until the circuit DEG is in resonance with the fundamental
frequency of the alternator. When that point is reached then the electromotive
force induced on the line X Y is to all practical purposes a simple harmonic and it
is very much higher than the impressed electromotive force although the number
of turns in the secondary coils of the two transformers CD and E F be the same
as in the primary coils. Fig. 8 illustrates one of the methods of employing the artifice
just described for multiple telegraphy. The disposition of circuits is just the same
as that given in Fig. 6 except that an auxiliary coil J is introduced in the
intermediate circuit and in shunt with this coil is a key j, the connecting wires
leading from a to c and from 6 to d. The electromagnetic constants of the
circuit D E G J are such as to render this circuit resonant to the fundamental of
the alternator when J is short-circuited by the depression of the key j. Hence
whenever this key is depressed there is a resonant rise of current in the circuit DE G
and, therefore, a large induced electromotive force on the line; but when the key
is open then the current in the circuit D E G sinks down to a very small value,
and, therefore, the electromotive force induced on the line X Y is also very small.
It is evident that if the line X Y has at its distant end a number of receiving
resonant circuits, such as illustrated in Fig. 6, then the sounder of that receiving
circuit which is resonant to A will act whenever the key is depressed. Employing,
therefore, a similar transmitting circuit for every receiving circuit I have a system
of multiplex telegraphy in which each transmitting station impresses a simple
harmonic electromotive force upon the line, the method of impressing the electro-
motive force consisting in adjusting, by the depression of the transmitting key, the
electromagnetic constants of the inducing circuit in such a way as to render it
resonant to the electromotive force which is to be impressed.
It is evident that the inducing circuit can be rendered resonant in many other
ways, as for instance by the arrangement of the circuits represented in Fig. 9 and
Fig. 10.
In all these arrangements the ultimate end in view is to reduce to a
minimum the impedance of the inducing circuit to the electromotive force which is
to be impressed by it upon the line.
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. A system of multiplex electrical signaling on which the operating electro-
motive forces are impressed upon the line at the transmitting end thereof by means
of inducing circuits whose electromagnetic constants are adjusted in such a way as
to render each of these circuits resonant to one of the electromotive forces to be
impressed upon the line, whereby each electromotive force thus impressed is a
simple harmonic.
2. A system of multiplex electrical signaling in which the receiving circuits are
in shunt with line condensers and the electromagnetic constants of these receiving
shunt circuits are proportioned by means of adjustable coils and condensers in such
a way as to render them resonant each to a separate electromotive force of definite
frequency impressed upon the line at the transmitting end thereof.
3. A system of multiplex electrical signaling in which the operating electromotive
forces are impressed upon the line at the transmitting end thereof, by means of
inducing circuits whose electromagnetic constants are adjusted in such a way as to
render each of these circuits resonant to one of the electromotive forces to be

page_text: impressed upon the line, whereby each electromotive force thus impressed is a
simple harmonic, and in which the receiving circuits are in shunt with line
condensers and the electromagnetic constants of these receiving shunt circuits are
proportioned by means of adjustable coils and condensers in such a way as to
render said receiving shunt circuits resonant each to a separate electromotive force
of definite frequency impressed upon the line at the transmitting end thereof.
Dated this 30th day of June 1895.
For the Applicant,
W. LLOYD WISE,
46 Lincoln's Inn Fields, London, W.C., Chartered Patent Agent.