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US 4,060,700 AGranted
Two-party telephone system
AssigneeTelefonaktiebolaget L M Ericsson
InventorSten Evert Magnusson
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AssigneeTelefonaktiebolaget L M Ericsson
InventorSten Evert Magnusson
Estimating the term…
The present invention relates to a two-party telephone system intended for external calls to and from each of the telephone sets included in the system, and speech connection between said telephone sets and conference calls between the telephones and an external subscriber. All these facilities are achieved through a two-wire connection between the telephones and require transmission of at least three different information conditions between the extensions included in the system. Each of the telephone sets comprises a visual indicating means I.alpha. for busy marking and a voltage source E which by connecting its voltage through the two-wire line activates the device I.beta. in the other telephone. An acoustical indicating means BZ which is activated by polarity reverse in said voltage source in the other telephone is also included in order to indicate that the telephone in which the polarity reverse has occurred wishes speech connection. To each telephone in the system is also connected an eavesdrop indicating means I.beta. which is activated in both the telephones when the voltage through the control device is increased by series connection of said voltage sources in order to indicate unintentional monitoring and that, at external call, both the telephones are connected respectively.
In a two-party telephone system utilizing a two-wire line, apparatus for enabling an external call to and from each of two telephone sets included in the system, an internal speech connection between said telephone sets and conference calls between the telephone sets and an external subscriber, said apparatus comprising, in order to achieve transmission of at least three different information conditions between said telephone sets in the system through a two-wire line, for each telephone set a control means, said control means comprising a first indicating means for busy marking connected between the conductors of said two-wire line, a voltage source, switching means for connecting said voltage source to said two-wire line with a first and a second polarity respectively, second indicating means for receiving a calling signal connected to said two-wire line, said first indicating means being responsive to said first polarity on said line and said second indicating means being responsive to said second polarity on said line, means for connecting said voltage sources in series to said two-wire line so that an increased voltage occurs between the two conductors of said two-wire line if both telephone sets are connected to the external line, said control means furthermore comprising third indicating means responsive to said increased voltage.
Dependencies are inferred from the claim text.