Loudspeaking telephone

Claim 2

In a loudspeaking telephone set, in combination, an audio loop including a transmit and a receive channel connectable to a telephone line by way of a hybrid, wherein said transmit channel includes a transmit amplifier and wherein said receive channel includes a receive amplifier, means including a linear adder for combining signaLs derived from the input and the output of said receive amplifier, a comparator circuit having a first input for receiving signals derived from speech signals on said transmit channel, a second input for receiving signals derived from noise on said transmit channel, and a third input for receiving signals derived from speech on said receive channel, means for applying the output of said adder to said third input, first and second variolosser circuits in said transmit and receive channels, respectively, and switching means for applying outputs from said comparator circuit to said variolosser circuits thereby to control the operating mode of said set.

Claim 3

Apparatus in accordance with claim 1 wherein said second variolosser circuit is connected in the feedback path of said receive amplifier.

Claim 4

Apparatus in accordance with claim 1 including first, second and third rectifying means for applying signals to said first, second and third inputs. respectively, a common control amplifier for amplifying both noise and speech signals derived from said transmit channel and for applying said last named signals so amplified to said first and second rectifying means, and a switchguard amplifier for amplifying the output of said adder and applying said last named output so amplified to said third input.

Claim 5

Apparatus in accordance with claim 3 wherein said common control amplifier and said switchguard amplifier each includes a respective feedback path comprising range expander circuitry.

Claim 6

Apparatus in accordance with claim 3 wherein said hybrid comprises an active network including a transistor substantially isolating said receive channel from transmitted speech signals and substantially isolating said transmit channel from received speech signals.

Claim 7

In a loudspeaking telephone set, in combination, an audio loop including a transmit and a receive channel, and means for switching gain in complementary fashion into said channels, said means including first and second substantially identical variolossers each connected in a respective one of said channels, each of said channels further including a respective amplifier, said variolosser in said receive channel being connected in the feedback network of said amplifier in said receive channel, control circuitry for applying control signals to said variolossers, wherein said control circuitry comprises a comparator circuit having a first input point for applying signals thereto derived from speech signals on said transmit channel, a second input point for applying signals thereto derived from noise on said transmit channel and a third input point for applying signals thereto derived from speech signals on said receiver channel, said comparator circuit generating an output signal at one of two output points as determined by the relative magnitude of signals applied to said input points, said control circuitry further including a transmit switch for applying signals from one of said output points to one of said variolossers, a talk-down switch for applying signals from the other of said two output points to the other of said variolossers, said signals derived from speech signals on said receiver channel being applied to said third input point by way of a linear adder circuit, an amplifier, and a rectifier in series relation, said receive channel including an amplifier and means connecting both the input and output sides of said amplifier to respective inputs of said linear adder circuit.

Claim 8

In a loudspeaking telephone set, in combination, an audio loop including a transmit and a receive channel, and means for switching gain in complementary fashion into said channels, said means including first and second substantially identical variolossers each connected in a respective one of said channels, each of said channels further including a respective amplifier, said variolosser in said receive channel being connected in the feedback network of said amplifier in said receive channel, control circuitry for applying control signals to said variolossers, wherein said control circuitry comprises a comparator circuit having a first input point for applying signals thereto derived from speech signals on said transmit channel, a second input point for applying signals thereto derived from noise on said transmit channel and a third input point for applying signals thereto derived from speech signals on said receiver channel, said comparator circuit generating an output signal at one of two output points as determined by the relative magnitude of signals applied to said input points, said control circuitry further including a transmit switch for applying signals from one of said output points to one of said variolossers, a talk-down switch for applying signals from the other of said two output points to the other of said variolossers, said signals derived from speech signals on said receiver channel being applied to said third input point by way of a linear adder circuit, an amplifier, and a rectifier in series relation, said receive channel including an amplifier and means connecting both the input and output sides of said amplifier to respective inputs of said linear adder circuit.