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Патент USA US2121287

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June 21, 1938.
EA. CQWAN
2,121,287
COMPOSITE SET
Filed March 3, 1937
LINE
’TEL [PHONE
FIG. 2
TELEPHONE
LINE
'
1-1
NETWORK
C3
_[__U-
TELEGRAPH
2
.
I.
FIG. 3
L/
LINE { -
W
‘
.
C‘ 2: ==c4
L!
{_‘
,
J
c:,’__= 2::(‘3
L2
TELEPHONE
-} TELEGRAPH
W
W
W
.
W
}BALA/VC/NG
NET ORK
L2
/N VEN TOR
By FA .COWA N
A 7'TORNEV
Patented June 21., 1938
_ 2,121,287
UNITED STATES PATENT OFFICE
2,121,287
_
COBIPOSITE SET
Frank Augustus Cowan, New York, N. Y., assignor
to American Telephone and Telegraph Com
pany, a corporation of New York
Ap?ication March 3, 1937, Serial No. 128,839
3 Claims.
This invention relates to multiplex signaling
systems and more particularly to improvements
in arrangements, such as composite sets, usually
associated with the terminal facilities of the lines
5 of such systems to prevent the different currents
utilized from interfering with each other:
An object of the invention is to permit the
interconnection of two communication circuits,
employing currents of di?erent frequencies, with
(Cl. 179--4)
ground assist in suppressing noise from the tele
graph circuit which might producev cross-talk
into the telephone circuit.
Condensers C4 serve
to exclude telegraph currents from the telephone
circuit and coils L1 serve to exclude telephone 5
currents from the telegraph circuit. " Coils L2 and
condensers C3 are then added as indicated to
provide balancing arms for a Wheatstone bridge ‘
and network I is added to simulate and balance
the line impedance. The functions of these eleand frequency descriminatlon .will be established merits may be more ‘readily perceived in Figs. 2
between said circuits, and between the transmis
and 3. It is apparent from these two ?gures
sion line and the balancing network of the com
that the network I simulating the line im
posite set, and frequency discrimination will be pedance, cannot absorb an appreciable amount
provided. between -each communication circuit of the telephone currents from the telephone
and the balancing network whereby energy dis
line because of the high impedance offered such
sipation in the balancing network will be reduced. currents by coils Lz nor can it absorb an appre
In common with other composite sets it is the ciable amount of energy from the telegraph cir
function of the composite set of this invention cuit because of condensers C3.
20 to permit the simultaneous‘ use of both telephone
From Fig. 3 it is apparent that the conditions
and telegraph facilities or the like over a common
for balance of the bridge circuit are that L1==Le
system of transmission lines, to permit the sepa
and 03:04. For satisfactory operation the im
ration of the telephone and telegraph currents pedance of the bridge, which is equal to the im
at terminals and to prevent interference between pedance of one of its four equal arms, should
‘the currents of these facilities. The composite equal the impedance of the lines connecting
set of.this invention makes use of the well-known - thereto.
combined balance and frequency discrimination
The bridge of this invention may be considered
which may be obtained by a Wheatstone bridge as a device for interconnecting two pairs of cir
employing reactive elements.
cuits so that the circuits of each pair will be
The composite set of this invention is similar conjugate and so that transmission to and from
30
to that shown and described in United States either circuit of one pair employing currents of
Patent 1,681,216 issued August 21, 1928 to D. E. diiferent frequencies, for example, telephone
Branson and R. B. Shanck, except that by a re
telegraph circuits, will tend to be excluded from
arrangement of the elements of the bridge cir
a particular circuit, viz. the balancing network
35 cuit the set‘ of this invention tends to exclude circuit, of the other conjugate pair. This reboth the telephone and telegraph currents from sults in more efficient operation than with the
the balancing network. In the composite set of usual devices of the prior art in which these cur
the above patent approximately half the energy rents divide equally between the transmission
of both telephone and telegraph transmission is line and the balancing network. '
40 dissipated in the balancing network.
For perfect balance of the bridge of this in
The invention may be more fully understood vention the line .and balancing network im
from the following description together with the pedances should be equal and the impedances of
accompanying drawing in Figs. 1, 2 and' 3 of the two communication circuits should be equal.
which the invention is illustrated‘:
In practice these impedances need be only reason
Figure 1 shows a circuit diagram embodying ably well matched for satisfactory operation.
a preferred form of the invention.
It is to be understood of course that the ar
Fig. 2 shows in diagrammatic form the com
rangement shown in the drawing and described
posite set of this invention; and
'
hereinbefore is purely diagrammatic and illus
Fig. 3' shows in schematic form the bridge trative of the principle involved and that the
50. circuit employed.
invention is' capable of embodiment in different
In Fig. 1 is shown a line circuit connected forms without departing from the spirit of the
through condenser C4 to a telephone circuit and invention and the scope of the appended claims.
through retardation coils L1 to a pair of tele
What is claimed is:
graph legs. Condensers C1 shunted across the
-1. Static means for interconnecting a trans
telegraph
circuit
and
provided
with
a
midpoint
55
mission line with a telegraphic circuit and a
10 a common transmission line, so that both balance
19
16
20
25
45
2,121,287
telephone circuit, said means including a line
balancing network and a Wheatstone bridge,
each arm of said bridge comprising an inductance
and a capacity in series, said arms being con
nected so 'that at each Junction of two arms of
said bridge-an inductance of one arm connects
with a capacity of the vother arm whereby in ad
dition to the usual balance and frequency dis
crimination between the telegraphic and tele
10 phone circuits, discrimination against the dissi
pation of both telegraphic and telephone cur
rents in the line balancing network is obtained.
2. Static means for interconnecting a trans
mission line with two communication circuits
employing currents of different frequencies, said
means including a line balancing network and a
Wheatstone bridge each arm of said bridge com
prising a plurality of unlike reactances in series,
said arms being connected so that at each junc
20 tion of two arms of said bridge, unlike reactances
are connected together whereby in addition to
the usual balance and frequency discrimination
between said two communication circuits, dis
crimination against the dissipation of currents
of both circuits in the line balancing network
is obtained.
3. Static means for interconnecting two pairs
of circuits, the circuits 01’ each pair being made
conjugate through said means, the circuits of
the ?rst of said pairs being designed to transmit
and receive currents of different frequencies, said
static means including a Wheatstone bridge each 10
arm of said bridge comprising an inductance
and a capacity in series, said arms being con
nected so that at each junction of two arms of
said bridge an inductance of one arm connects
with a capacity of the other arm whereby, in
addition to the usual balance and frequency dis
crimination between the circuits of said ?rst pair,
discrimination against the dissipation of cur
rents of both said ?rst pair of circuits in a par
20
ticular circuit of said second pair is obtained.
FRANK AUGUSTUS COWAN.
I.
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