Relay range extender for telephone systems

Claim 1

In a telephone transmission circuit, a telephone having a hookswitch, central office line equipment for said telephone, a two-conductor telephone transmission line having first and second conductors, and a relay range extender for increasing the amount of operating current fed to said line equipment without electrically disconnecting said telephone from the central office in which said line equipment is located, said relay range extender comprising a balanced two-winding relay and resistor means, said relay having a set of normally open contacts and a pair of windings which have substantially equal resistances and which are respectively connected to and in series with said first and second conductors, said telephone being electrically connected by said line and said windings to said line equipment, said windings, said conductors and said hookswitch being connected in a loop circuit to provide for current flow serially through one of said windings, said first conductor, said hookswitch, said second conductor and the other of said windings, said resistor means and said set of normally open contacts being connected in series in a circuit branch which is in parallel with said loop circuit, said hookswitch being effective upon closure to complete a circuit through said loop circuit for energizing said windings and for maintaining said windings energized as long as said hookswitch is closed, and said set of contacts being closed by energization of said windings to complete a circuit which electrically connects said resistor means in parallel with said loop circuit and in series with at least one relay in said line equipment as long as said hookswitch is closed, said resistor means having a pre-selected resistance which when connected in parallel with said loop circuit branch by closure of said set of contacts increases the operating current for said line equipment relay over the value that it would have if said resistor means were not connected in parallel with said loop circuit without reducing the telephone operating current fed through said loop circuit below the amount needed for operation of said telephone. Referring to the drawing, the telephone transmission circuit, which incorporates the principles of this invention, is generally indicated at 10 and comprises a subscriber''s telephone 12 of conventional construction, a two-conductor telephone transmission line 14, conventional central office line equipment 16 and a relay range extender 18. The conductors of line 14 are indicated at 19 and 20 respectively. Conductors 19 and 20 are conventionally connected to operating terminals of telephone 12 which is remote from the central office.