Improvements in Methods of and Apparatus for Preventing the Interference with Speech on Telephone Circuits by Induced and other Currents.
Year: 1891

page_text: Date of Application, 4th June, 1891-Accepted, 11th July, 1891
COMPLETE SPECIFICATION.
Improvements in Methods of and Apparatus for Preventing the
Interference with Speech on Telephone Circuits by Induced and
other Currents.
We, WILLIAM STANLEY Jr., of Pittsfield, County of Berkshire and State of
Massachusetts,. Post Office address, Pittsfield, Massachusetts, Electrician, and
JOHN FORREST KELLY, of New York, County and State of New York, Post
Office address, 29 Plane Street, Newark, New Jersey, Electrician, both of United
States of America, 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:-
It is a well known fact that the self-induction and capacity of an electric circuit
over which a current of a given periodicity or number of waves per unit of time is
flowing, may be adjusted relatively to each other and to the said current, so that
only the dead resistance of the circuit will be opposed to the passage of such
currents.
In general, if n be used to denote the number of complete waves of the current
per second I, the coefficient of self-induction of the circuit, and M its capacity in
microfarads, then any line that possesses the necessary values of L and M in the
equation
-(the mathematical expression of the law, in which the other factors are constants
that need not be considered herein)-will offer no other opposition to a current of
waves than that of ohmic resistance.
It is obvious, however, that for all other frequencies an opposition other than
that of ohmic resistance will appear; for higher frequencies, due to an unbalanced
self-induction, for lower to an unbalanced capacity. It is clear, moreover, that as
the capacity introduced continues to neutralize the self-induction to some extent for
all frequencies, that all rates above the normal will get through more readily than
if no capacity were present although the farther they are from the normal the less
will they be helped. It is otherwise with lower frequencies. Here the opposition
is due to the capacity, the new element introduced into the circuit, and for rates a
certain amount below the normal, the opposition offered by the unbalanced con-
denser is greater than that previously afforded by the self-induction alone.
Our present invention consists in a method of and apparatus for lessening or
preventing the interference with the reproduction of articulate speech in telephones
which is caused by induction from neighbouring telegraph lines or electric light or
power circuits, which are based or dependent upon the above law.
In carrying out our invention we interpose in the circuit, between the receiving
phone and the line, a self-induction coil and a condenser, to which such values are
given that they will operate to hinder to the greatest possible extent the pro-
pagation of current waves of a frequency below a certain predetermined limit, but
permit the speech-producing currents which are of much higher frequency to pass
without material opposition. This invention may be carried out in various ways,
as we shall now explain by reference to the accompanying drawings.
Figures 1, 2, and 3 are diagrams of several of the ways in which the invention is
or may be carried into effect. They will be explained in detail in their order.
Figure 1 Let A designate any telephone line and P a receiving phone con-
nected therewith, the line being grounded at G.
If the line A be in inductive proximity to an alternating current lighting, or

page_text: power or other circuit over which currents of a comparatively low number of waves
are passing, the disturbance produced in the phone by induction may be so great as
to practically prevent the intelligible transmission of speech. To arrest or oppose
the disturbing currents, we introduce into the circuit between the receiver and the
line a given self-induction and capacity, or, in other words, a self-induction coil L
and a condenser C. The relative values of these devices may be readily adjusted
by varying the length of the coil and the size of the condenser, so as to hinder to a
very great extent the propagation of waves of a frequency below a predetermined
limit, while checking to but a slight extent or even favouring those corresponding
to and producing speech-so that telephonic communication may be carried on
without serious interference from those induced or leakage currents that now so
frequently render such communication impossible.
In Figure 2, this arrangement is modified by the addition of a shunt S from line
to ground around the condenser and the receiver which is so adjusted as to capacity
and self-induction, by means of a condenser C' of comparatively large capacity and
a self-induction coil L' of comparatively low self-induction, as to possess a high
degree of receptivity for long waves.
In Figure 3 is shown a similar arrangement, except that the shunt S is arranged
to have a high self-induction and low resistance, which would tend to shunt the
long waves and oppose the short.
So in various ways there may be placed in the circuit a means of hindering the
propagation of long waves in the coils of the receiving phone, while not checking
those corresponding to sound waves, and such long waves may be shunted around
the said receiver by a circuit of high receptivity for such waves or of a low degree
of receptivity for those corresponding to articulate speech.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed we declare that
what we claim is :-
First. The method herein described, of preventing the action of currents of low
frequency on a receiving instrument in a circuit over which currents of low and
currents of high frequency are passing, by hindering or checking the currents of
low frequency in their passage to said receiver, as set forth.
Second. The method herein described, of preventing the action of currents of low
frequency on a receiving instrument in a circuit over which currents of low and
currents of high frequency are passing, by hindering or checking the currents of
low frequency in their passage to, and diverting or shunting them around the
receiver, as set forth.
Third. The combination with a telephone line and a receiver contained therein,
of a self-induction coil and a condenser adjusted or adapted to hinder or check
current waves below a predetermined frequency and inserted in the circuit between
the receiver and the line, as set forth.
Fourth. The combination with a telephone line and a receiver contained therein,
of a self-induction coil and a condenser for hindering or checking current waves
below a predetermined frequency in their passage to the receiver, and a shunt
circuit around said condenser and receiver of high receptivity for such waves, as
herein set forth.
Fifth. The combination with a telephone line, of two branches at the receiving
end one being adjusted or adapted to oppose currents of low frequency and
including the receiver, the other being of high receptivity for such currents, as set
forth.
Dated this 4th of T1001
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicants.