US 4,310,723 AGranted

Party line apparatus

OwnerCarl G. Svalainventor

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Abstract

Privacy and selective ringing in a two-party line system are implemented by using unidirectional diodes in the speech circuit and the ringer circuit, respectively, of the subscriber instruments. The diodes in the first subscriber instrument are oppositely poled with respect to those in the second subscriber instrument. Current sensors, in response to the application of a DC biased AC monitoring signal, provide party identification by sensing the direction of current flow in the line. Line terminal apparatuses are then switched onto the line, in response to the party identification current sensors, to provide the correct line polarity for the identified party.

Claims8

Dependent claims

In a party line telephone arrangement having:

first and second subscriber instruments each including a bell circuit, a speech circuit with a cradle switch, and a pair of transfer terminals;
first and second subscriber lines with subscriber ends connected to the respective terminals of the pair of transfer terminals and central terminal ends;
and a central office including first and second line terminal apparatuses respectively assigned to the first and second subscriber telephones, each of said line terminal apparatuses including first and second terminals being at, during a non-ring state, a reference voltage level and a bias voltage level respectively, the improvement comprising:
first unidirectional conducting means for connecting the speech circuit of the first subscriber instrument between the pair of transfer terminals thereof whereby current can only flow in a first direction through the first and second subscriber lines;
second unidirectional conducting means for connecting the speech circuit of the second subscriber instrument between the pair of transfer terminals thereof whereby current can only flow in a second and opposite direction through the first and second subscriber lines;
first further unidirectional conducting means for connecting the bell circuit of the first subscriber instrument between the transfer terminal thereof connected to the first subscriber line and a given reference voltage whereby current can flow through the bell circuit only in a given direction;
second further unidirectional conducting means for connecting the bell circuit of the second subscriber instrument between the transfer terminal thereof connected to the second subscriber line and said given reference voltage whereby current can flow through the bell circuit thereof only in said given direction;
source means for applying a d.c.-biased alternating current monitoring signal to central terminal ends of the first and second subscriber lines respectively, the instantaneous amplitude of said monitoring signal being no greater than said reference voltage;
first switching means associated with one of the subscriber instruments and operative upon sensing the flow of current through the subscriber lines in a first direction for switching the connection of the central terminal ends of the subscriber lines from said source means to the terminals of the first line terminal apparatus whereby the d.c. potential of one subscriber line is greater than the d.c. potential of the other subscriber line;
and second switching means associated with the other of the subscriber instrument and operative upon sensing the flow of current through the subscriber lines in a second and opposite direction for switching the connection of the central terminal ends of the subscriber lines from said source means to the terminals of the second line terminal apparatus whereby the d.c. potential of said one subscriber line is less than the d.c. potential of said other subscriber line.

7 more elements

Dependencies are inferred from the claim text.

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Abstract

In a party line telephone arrangement having:

first and second subscriber instruments each including a bell circuit, a speech circuit with a cradle switch, and a pair of transfer terminals;
first and second subscriber lines with subscriber ends connected to the respective terminals of the pair of transfer terminals and central terminal ends;
and a central office including first and second line terminal apparatuses respectively assigned to the first and second subscriber telephones, each of said line terminal apparatuses including first and second terminals being at, during a non-ring state, a reference voltage level and a bias voltage level respectively, the improvement comprising:
first unidirectional conducting means for connecting the speech circuit of the first subscriber instrument between the pair of transfer terminals thereof whereby current can only flow in a first direction through the first and second subscriber lines;
second unidirectional conducting means for connecting the speech circuit of the second subscriber instrument between the pair of transfer terminals thereof whereby current can only flow in a second and opposite direction through the first and second subscriber lines;
first further unidirectional conducting means for connecting the bell circuit of the first subscriber instrument between the transfer terminal thereof connected to the first subscriber line and a given reference voltage whereby current can flow through the bell circuit only in a given direction;
second further unidirectional conducting means for connecting the bell circuit of the second subscriber instrument between the transfer terminal thereof connected to the second subscriber line and said given reference voltage whereby current can flow through the bell circuit thereof only in said given direction;
source means for applying a d.c.-biased alternating current monitoring signal to central terminal ends of the first and second subscriber lines respectively, the instantaneous amplitude of said monitoring signal being no greater than said reference voltage;
first switching means associated with one of the subscriber instruments and operative upon sensing the flow of current through the subscriber lines in a first direction for switching the connection of the central terminal ends of the subscriber lines from said source means to the terminals of the first line terminal apparatus whereby the d.c. potential of one subscriber line is greater than the d.c. potential of the other subscriber line;
and second switching means associated with the other of the subscriber instrument and operative upon sensing the flow of current through the subscriber lines in a second and opposite direction for switching the connection of the central terminal ends of the subscriber lines from said source means to the terminals of the second line terminal apparatus whereby the d.c. potential of said one subscriber line is less than the d.c. potential of said other subscriber line.

7 more elements