Improvements in Multiplex Telephony.
Year: 1895

page_text: Improvements in Multiplex Telephony.
I, DANIEL SINCLAIR, Engineer-in-chief, to The National Telephone Company
(Limited), Oxford Court, Cannon Street, in the City of London, do hereby declare
the nature of this invention to be as follows:-
This invention relates to improvements in multiplex telephony, and has for its
object the simplification and improvement of the arrangements at present in use
for this purpose, and the attainment of better results.
Several systems of multiplex telephony have been in use for a considerable time,
but while these were suitable for working between two fixed points they did not
provide for the necessary exchange switch-board arrangements. Hitherto, special
resistances in the form of bridges, or otherwise, have always been necessary; but
these special resistances have a detrimental effect upon conversation over the lines
and by this invention these are rendered unnecessary.
For this purpose I employ instead of the ordinary indicator a special indicator,
which, in addition to fulfilling the requirements of an ordinary indicator, acts as a
multiplex coil in a manner superior to any device hitherto used for this purpose.
The coil of this indicator is specially wound so that when a ringing current is sent
over the main circuit it passes through the coil in the ordinary way and drops the
shutter, but this indicator is not operated when a current is sent on the duplex or
extra circuit. These indicators may be made in various forms, sheathed in a solid
soft iron tube or having a laminated covering to complete the magnetic circuit.
When used in conjunction with earth circuits which have to be connected to
metallic circuit lines, the coils are specially inade and wound with an extra circuit
which extra circuit acts in conjunction with the other to form a telephonic
translator. The coils may be wound in various ways and to various resistances.
Preferably, I use them differentially wound, and of a resistance of 1000 ohms when
in bridge across a metallic circuit.
These multiplex indicators, or combined indicator, translator and multiplex coil
may be used in various ways. For example in one combination or arrangement
six earth circuit subscribers' wires, viz., three at each end, are connected together
through two metallic circuit trunk or junction lines the earth circuits being
connected to one winding of the coils and the trunk or junction lines to the other.
This combination may be extended by joining the centre point of the coils of the
extra circuit through spring-jacks or telephones to the centre point of a similar
combination, and this combination may again he extended in a similar manner.
The improvement effected is that with this combination no other indicator is
necessary either on the local or main circuit for calling-up or ringing-off purposes,
and there are, therefore, no shunts or resistances in the circuits tending to cut
down the efficiency of the circuit.
In a similar combination of these multiplex indicators applied to metallic
circuits for subscribers six metallic circuit lines are similarly connected together
through two metallic circuit trunk or junction lines, and this can be extended
further in the manner above indicated. The improvement effected in this case is
that no shunt other than the multiplex indicator shunt is necessary at each end, so
that main circuits having superimposed circuits are in exactly the same condition
as regards shunts as they are for general use.

page_text: In another combination of these multiplex indicators, three subscribers' circuits
are carried to the exchange by two metallic circuits, each subscribers' circuit
being practically independent and dropping its respective indicator; and this
combination can be extended in the manner indicated above. At the exchange,
the special multiplex indicators are used, and at a conveniently placed distributing
point multiplex ceils in connection with the same, in every way as before
described, but having no shutter or other indicating arrangements, are bridged
across the main circuits, and to the centre points of these coils the extra
circuit is attached. The improvement effected is that the number of shunts
necessary is reduced to the minimum.
In a further combination of these multiplex indicators, two multiplex_combina-
tions such as above described with reference to the earth circuits and metallic
circuits are joined together. For this purpose, a special, and preferably differential
and equally-wound four-coil multiplex translator-indicator is used, which is placed.
between the main circuits that are to be joined together. By this arrangement
there are no shunts across the circuits at the exchange where these lines are
joined together. This special translator keeps the superimposed circuits intact
while the main circuits are extended.
WALLACE FAIRWEATHER,
Chartered Patent Agent,
2 St. Vincent Street, Glasgow, Agent for the Applicant.
Improvements in Multiplex Telephony.
I, DANIEL SINCLAIR, Engineer-in-chief, to The National Telephone Company
(Limited). Oxford Court, Cannon Street, in the City of London, 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 improvements in multiplex telephony, and has for its
object the simplification and improvement of the arrangements at present in use for
this purpose, and the attainment of better results.
Several systems of multiplex telephony have been in use for a considerable time,
but while these were suitable for working between two fixed points, they were not
adapted for an exchange system without being provided with special resistances in
the form of bridges, or otherwise, in addition to the ordinary switchboard
apparatus. These special resistances had a detrimental effect upon conversation
over the lines, and are by this invention rendered unnecessary.
To accomplish this I provide in the place of the ordinary indicator one specially
wound, which, in addition to fulfilling the requirements of an ordinary indicator,
acts as a multiplex coil, and fulfils its purpose in a manner superior to any device
hitherto used. The coil of this indicator is specially wound so that when a
ringing current is sent over the main circuit it passes through the coil in the
ordinary way, attracts the armature, and so drops the shutter, but the indicator
is not energized when a current is sent through the centre point. The indicator
may be of various forms, sheathed in a solid soft iron tube, or having a laminated
covering to complete the magnetic circuit, and when used in conjunction with
earth circuits which have to be connected to metallic circuit lines it is wound with
an extra circuit which acts in conjunction by induction with the circuit before
mentioned, and so forms a telephonic translator. The coils may be wound in

page_text: various ways, and to various resistances. Preferably, I use them differentially
wound, and of a resistance of 1000 ohms.
These multiplex indicators, or combined indicator, translator, and multiplex
coils, may be used in various ways as illustrated by the diagrammatic figures of
the accompanying drawings.
In Figure 1 six earth circuit subscribers' wires a¹, a³, a³, a, a, a, are shown
connected through exchanges A and B, three on each exchange, by two metallic
circuit trunk or junction wires L and M. Each subscribers' line a¹ to a' is
connected by means of the ordinary switchboard arrangements, (which for the sake
of clearness I have omitted from the drawings) to one coil of the multiplex
indicators and translators 61, 62, 63, 64, 6, 6, respectively and the trunk or junction
wires L and M to the other coils of the indicators and translators b¹, 63, 6 and 6ª.
The second coils of the indicators and translators 6 and 6' are connected to the
centre points of 61 and 68 and 64 and 6 respectively. This combination may be
further extended by taking a connection from the centre points of the indicators b
and to one side of similar coils as shown in dotted lines c, d, and thence to the
centre points of a similar combinatiou, and this combination may be again extended
in a similar manner. It will thus be seen that subscriber a when ringing on the
line only energizes indicators 6, 6. Although indicators 6', 63, 64, 6, are in the
circuit they are not affected as the current passes from indicator 6' to the centre
points of indicators 6 and 63, through the two halves of these coils in opposite
directions, thereby neutralizing any magnetic effect, along the two wires of each
junction Ĺ and M, through the indicators 6 and 66 in opposite directions to the
centre point and thence through the indicator b*. It will be observed that there
are no shunts on the circuits tending to reduce the efficiency of the same.
In Figure 2 a similar combination to that described above, but for metallic
circuit subscribers' lines, is shown. Six metallic circuit subscribers' lines d', dª, d³,
d', d', d, are shown connected through exchanges C and D, three on each exchange,
by two metallic circuit trunk or junction lines O and P. The subscribers' lines
are connected by means of the ordinary switchboard arrangement (omitted from
the drawings). It will be noticed on this arrangement that it is unnecessary
to wind the indicators e¹, e³, e³, e, e, e, with two separate coils, as both the
subscribers' and the junction lines being metallic circuits the indicators are used as
multiplex coils only, and not as telephone translators as described in connection
with Figure 1. The results as regards ringing are the same as described in
connection with Figure 1. The combination may be also extended by con-
nections, shown in dotted lines from the centre points of indicators e
and e³.
The improvement effected in this case is that no shunt, other than the multiplex
indicator shunt, is necessary, so that the main circuits, although having super-
imposed circuits, are in exactly the same condition as regards shunts as an ordinary
telephone line.
In Figure 3 a combination of my multiplex indicators and bridging coils is
shown, by which means three metallic circuit subscribers' lines g', g, g³, are
brought into the exchange E from a distributing point F by means of two metallic
circuit main lines and R at the distributing box F, at which point differentially
wound coils and bridge the main lines. To the centre points of these coils
the two wires of metallic circuit subscriber 9 are connected. At the exchange
end the two main circuits Q and R are brought through jacks to multiplex
indicators. The centre points of these indicators are connected to the
indicator belonging to the line shown at . This combination may be further
extended by taking a connection from the centre point of indicator at exchange E
and the centre point of bridging coil ' at distributing box F to one side of similar
coils and, and thence to the centre point of a similar combination as previously
described. The results as regards ringing are the same as described in connection
with Figure 1.
In Figure 4 a further application of my indicator, translator, and multiplex

page_text: coil is shown, where H represents an exchange on metallic circuit system, and K
an earth circuit system, and Ja junction or trunk wire exchange, and shows four
junction wires S and T, U and V; S and U being metallic circuit junction wires
between H and J, and T and V being metallic circuit junction lines between J
and K, joined together by means of the connecting cords and my multiplex
indicators P, P, preferably having four coils equally and differentially wound at
junction exchange J. By this means_conversation can be simultaneously carried
on between subscribers on exchange H and subscribers on exchange K, over the
junction lines S, T, and U, V; also between H and J, and J and K, on the super-
imposed circuits, or on the duplex circuit between H and K by joining the two
jacks m¹, m³, at J together by means of the usual switching apparatus. This
may be further extended by taking connections from the centre points of the
indicators n', n³, n³, n³, to one side of similar coils o¹, 03, 0, 1, (shown in dotted
lines) and thence to the centre points of a similar combination as previously
described.
This invention can only be used where the indicators are kept permanently in
shunt in the circuits, except in such a case as described at J Figure 4, where the
multiplex indicator and translator coils may be in the cord circuit, the junction
lines S, T, U, V, normally ending in multiplex indicators which are cut out of
circuit when the plug is inserted and two junction lines joined together, such
multiplex indicators being in derived circuit to the multiplex indicator translator.
This invention admits of modifications in the arrangement which would readily
suggest themselves to those skilled in the art. I therefore do not limit myself to
the precise arrangements shown or described herein.
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. The improved system of multiplex telephony herein before described under
several modifications with reference to the annexed diagrams.
2. A multiplex telephone system adapted for use with ordinary switchboard
arrangements and in which the indicators employed are wound and joined to the
main and extra circuits substantially in the manner described.
Doted thin 17th 1 ca
1
1000
WALLACE FAIRWEATHER,
Of the Firm of Cruikshank & Fairweather, Chartered Patent Agents,
62 St. Vincent Street, Glasgow, Agent for the Applicant.