Improved Method of and Means for Preventing Disturbances in Telephone Circuits by Alternating Current Installations.
Year: 1897

page_text: Date of Application, 15th Apr., 1897-Accepted, 5th June, 1897
Improved Method of and Means for Preventing Disturbances in
Telephone Circuits by Alternating Current Installations.
We, OTTO TITUS BLÁTHY and KOLOMAN KANDÓ, both of Hauptgasse 73,
Budapest II, Hungary, Engineers, 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 well known that alternating current circuits which are connected with
earth at several points or in which earth forms part of the circuit, have a
disturbing effect on the apparatus of adjacent telephonic circuits which also employ
earth as the return circuit.
These disturbances are caused by the fact that a portion of the vagabond
alternating currents pass through the telephone circuit and apparatus that are
connected with carth.
By this means the membranes of the telephone apparatus are put in oscillation
which cause sounds that unpleasantly disturb the telephonic communications.
Our present invention has for its object so to modify the current curve and
consequently the oscillations of the telephone membranes, by the employment of
suitable generators and motors of the alternating current installations, that no
audible tone is produced thereby.
This object is attained with currents that flow according to a simple sinusoidal
curve or a curve similar thereto, by making the frequency of the alternating current
lower than the frequency of the vibrations of the lowest tone perceptible by the
ear, and we have found that sinusoidal currents having a frequency of less than
20 periods per second produce no audible sound.
If however the current curve shews higher harmonic vibrations, as is the
case with motor installations, these produce a higher sound in the telephone
apparatus.
These higher harmonic vibrations are caused in motors where the air space is
exceedingly small, by the variation of the induction coefficient in consequence of
the motion of the teeth of the rotor relatively to the teeth of the stator.
This influence of the alternating currents on the telephonic circuits and apparatus
can be obviated in a simple manner by the employment of motors which, by means
of an oblique arrangement of grooves of the stator or of the rotor a as at Fig.1
of the accompanying drawing, or of the stator b as at Fig. 2, and of the rotor, in
Buch manner that the grooves of the stator are not parallel with those of the rotor,
as will be seen from the drawing.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
1. The method of preventing disturbances of telephone installations being
caused by single or polyphase alternating current installations in which earth
either forms one of the conductors or is connected to one of the conductors, by the
employment in such installations of alternating currents with a frequency of less
than twenty periods per second, substantially as described.
2. In a single or polyphase alternating current-installation in which the earth
either forms one of the conductors, or is connected to one of the conductors, the

page_text: employment of alternating currents having a frequency of less than twenty periods
per second, in combination with a construction of single or polyphase alternating
current motor having obliquely arranged armature grooves, for the purpose
preventing disturbances in telephonic apparatus, substantially as described.
Dated this 15th dow of Anvil 1907
of
ABEL & IMRAY,
Agents for the Applicants.