Telephone line equalizer

Claim 2

A telephone line equalizer circuit for compensating for the attenuation characteristics of telephone lines of varying attenuations comprising: input and output terminals for connecting said circuit in a telephone line; an operational amplifier means having a signal input, a feedback input and a signal output; first connecting means for connecting said signal input to said input terminal; second connecting means for connecting said signal output to output terminal; a voltage feedback means connecting said signal output to said feedback input, said voltage feedback means comprising a filter network having an electrical frequency characteristic substantially the same as the telephone line, a reference potential means, a resistive means connected between said signal output and said reference potential means, means for connecting said feedback input to said resistive means in such a way that the voltage developed across at least a fractional part of said resistive means is fed to said feedback input as a feedback signal, and controllable connection means for connecting said filter network in parallel with a selectable portion of said resistive means.

Claim 3

The telephone line equalizer circuit of claim 1 wherein said voltage feedback means comprises a reference potential means, a resistor and a potentiometer connected in series between said signal output and said reference potential means, means for connecting said feedback input to the junction of said potentiometer and said resistor and means for connecting said filter network between the wiper of said potentiometer and said reference potential means.

Claim 4

The telephone line equalizer circuit of claim 1 wherein one of said connecting means comprises A spot frequency amplifier means for modifying particular frequency signals.

Claim 5

The telephone line equalizer circuit of claim 3 wherein said spot frequency amplifier means comprises a further operational amplifier means having a signal input, a feedback input and a signal output, a reference potential means, a potentiometer means connected between the signal output of said further operational amplifier means and said reference potential means, a capacitor connected in parallel with at least a portion of said potentiometer means, and means for connecting the slider of said potentiometer means to the feedback input of said further operational amplifier means.

Claim 6

The telephone line equalizer circuit of claim 3 wherein said spot frequency amplifier means comprises an emitter-follower amplifier means including potentiometer means in the emitter circuit thereof, and a series circuit including an inductor and a capacitor connected to said potentiometer means and the slider thereof in such a way that said series circuit is in parallel with selectable portions of said potentiometer means.

Claim 7

A telephone line equalizer circuit for compensating for the attentuation characteristics of telephone lines of varying attenuations comprising: input and output terminals for connecting said circuit in a telephone line; an operational amplifier means having a signal input, a feedback input and a signal output; first connecting means for connecting said signal input to said input terminal; second connecting means for connecting said signal output to output terminal; and a voltage feedback means connecting said signal output to said feedback input, said voltage feedback means comprising, a reference potential means, a filter network having an electrical frequency characteristic substantially the same as the telephone line, said filter network comprising a pi-section including first and second legs each having a resistor and capacitor in series and a further capacitor in parallel therewith, an inductor and further resistor interconnecting one end of each of said legs and means for connecting the other ends of said legs to said reference potential means, and said voltage feedback means further comprises a potentiometer, means for connecting said potentiometer between said signal output and said reference potential means, means for connecting said feedback input to said potentiometer and means for connecting said one end of one of said legs of said filter network to the wiper of said potentiometer.

Claim 8

A telephone line equalizer circuit for compensating for the attentuation characteristics of telephone lines of varying attenuations comprising: input and output terminals for connecting said circuit in a telephone line; an operational amplifier means having a signal input, a feedback input and a signal output; first connecting means for connecting said signal input to said input terminal; second connecting means for connecting said signal output to output terminal; and a voltage feedback means connecting said signal output to said feedback input, said voltage feedback means comprising, a reference potential means, a filter network having an electrical frequency characteristic substantially the same as the telephone line, said filter network comprising a pi-section including first and second legs each having a resistor and capacitor in series and a further capacitor in parallel therewith, an inductor and further resistor interconnecting one end of each of said legs and means for connecting the other ends of said legs to said reference potential means, and said voltage feedback means further comprises a potentiometer, means for connecting said potentiometer between said signal output and said reference potential means, means for connecting said feedback input to said potentiometer and means for connecting said one end of one of said legs of said filter network to the wiper of said potentiometer.

Claim 9

A telephone line equalizer circuit for compensating for the attenuation characteristics of telephone lines of varying attenuations comprising input and output terminals for connecting said circuit in a telephone line, an operational amplifier means having a signal input, a feedback input and a signal output, first connecting means for connecting said signal input to said input terminal, second connecting means for connecting said signal output to output terminal, a voltage feedback means connecting said signal output to said feedback input, said voltage feedback means comprising a filter network having an electrical frequency characteristic substantially the same as the telephone line, and one of said connecting means comprises a further operational amplifier means having a signal input, a feedback input and a signal output, and a further voltage feedback means including a reference potential means, a further resistive means connected between the signal output of said further operational amplifier means and said reference potential means, means for connecting the feedback input of said further operational amplifier means to said further resistive means in such a way that the voltage developed across at least a fractional part of said further resistive means is fed to the feedback input of said further operational amplifier means as a feedback signal, a further filter network having an electrical frequency characteristic substantially the same as the telephone line, and controllable coNnection means for connecting said further filter network in parallel with a selectable portion of said further resistive means.

Claim 10

A telephone line equalizer circuit for compensating for the attenuation characteristics of telephone lines of varying attenuations comprising input and output terminals for connecting said circuit in a telephone line, an operational amplifier means having a signal input, a feedback input and a signal output, first connecting means for connecting said signal input to said input terminal, second connecting means for connecting said signal output to output terminal, a voltage feedback means connecting said signal output to said feedback input, said voltage feedback means comprising a filter network having an electrical frequency characteristic substantially the same as the telephone line, and one of said connecting means comprises a further operational amplifier means having a signal input, a feedback input and a signal output, and a further voltage feedback means including a reference potential means, a further resistive means connected between the signal output of said further operational amplifier means and said reference potential means, means for connecting the feedback input of said further operational amplifier means to said further resistive means in such a way that the voltage developed across at least a fractional part of said further resistive means is fed to the feedback input of said further operational amplifier means as a feedback signal, a further filter network having an electrical frequency characteristic substantially the same as the telephone line, and controllable coNnection means for connecting said further filter network in parallel with a selectable portion of said further resistive means.

Claim 11

A telephone line equalizer circuit for compensating for the attenuation characteristics of telephone lines of varying attenuations comprising: input and output terminals for connecting said circuit in a telephone line; an operational amplifier means having a signal input, a feedback input and a signal output; first connecting means for connecting said signal input to said input terminal; second connecting means for connecting said signal output to output terminal; and a voltage feedback means connecting said signal output to said feedback input, said voltage feedback means comprising a filter network having an electrical frequency characteristic substantially the same as the telephone line; and one of said connecting means is a spot frequency amplifier comprising an emitter-follower amplifier means including potentiometer means in the emitter circuit thereof, and a series circuit including an inductor and a capacitor connected to said potentiometer means and the slider thereof in such a way that said series circuit is in parallel with selectable portions of said potentiometer means, and a further operational amplifier means having a signal input, a feedback input and a signal output, a reference potential means, a further potentiometer means connected between the signal output of said further operational amplifier means and said reference potential means, a further capacitor connected in parallel with at least a portion of said further potentiometer means, means for connecting the slider of said further potentiometer means to the feedback input of said further operational amplifier means, and means for connecting the output of said further operational amplifier means to the input of said emitter-follower amplifier means, the input of said further operational amplifier means being the input of said spot frequency amplifier.

Claim 12

A telephone line equalizer circuit for compensating for the attenuation characteristics of telephone lines of varying attenuations comprising: input and output terminals for connecting said circuit in a telephone line; an operational amplifier means having a signal input, a feedback input and a signal output; first connecting means for connecting said signal input to said input terminal; second connecting means for connecting said signal output to output terminal; and a voltage feedback means connecting said signal output to said feedback input, said voltage feedback means comprising a filter network having an electrical frequency characteristic substantially the same as the telephone line; and one of said connecting means is a spot frequency amplifier comprising an emitter-follower amplifier means including potentiometer means in the emitter circuit thereof, and a series circuit including an inductor and a capacitor connected to said potentiometer means and the slider thereof in such a way that said series circuit is in parallel with selectable portions of said potentiometer means, and a further operational amplifier means having a signal input, a feedback input and a signal output, a reference potential means, a further potentiometer means connected between the signal output of said further operational amplifier means and said reference potential means, a further capacitor connected in parallel with at least a portion of said further potentiometer means, means for connecting the slider of said further potentiometer means to the feedback input of said further operational amplifier means, and means for connecting the output of said further operational amplifier means to the input of said emitter-follower amplifier means, the input of said further operational amplifier means being the input of said spot frequency amplifier.

Claim 13

A telephone line equalizer circuit for compensating for the attenuation characteristics of telephone lines of varying attenuations comprising input and output terminals for connecting said circuit in a telephone line, an operational amplifier means having a signal input, a feedback input and a signal output, first connecting means for connecting said signal input to said input terminal, second connecting means for connecting said signal output to output terminal, and a voltage feedback means connecting said signal output to said feedback input, said voltage feedback means comprising a filter network having an electrical frequency characteristic substantially the same as the telephone line, said filter network comprising a reference potential means, a pi-section including first and second legs each having a resistor and capacitor in series and a further capacitor in parallel therewith, an inductor and a further resistor interconnecting one end of each of said legs, and means for connecting the other ends of said legs to said reference potential means.

Claim 14

A telephone line equalizer circuit for compensating for the attenuation characteristics of telephone lines of varying attenuations comprising input and output terminals for connecting said circuit in a telephone line, an operational amplifier means having a signal input, a feedback input and a signal output, first connecting means for connecting said signal input to said input terminal, second connecting means for connecting said signal output to output terminal, and a voltage feedback means connecting said signal output to said feedback input, said voltage feedback means comprising a filter network having an electrical frequency characteristic substantially the same as the telephone line, said filter network comprising a reference potential means, a pi-section including first and second legs each having a resistor and capacitor in series and a further capacitor in parallel therewith, an inductor and a further resistor interconnecting one end of each of said legs, and means for connecting the other ends of said legs to said reference potential means.