Internal telephone intercom system

Claim 1

In an internal handsfree telephone intercom system including line connection means for connection to a designated pair of telephone communication lines, and a plurality of telephone sets having speakers connected to the line connection means and adapted for telephone communications with locations external to said lines by receiving and transmitting telephone signals within a first frequency range, the improvement comprising: a plurality of telephone sets with each having a first audio receiving means for receiving at each of said telephone sets, audio signals from a microphone within said telephone set; a radio frequency generator means at each of said telephone sets for generating a carrier frequency of a first frequency, the generator means being connected to the audio receiving means with the amplitude of the generator means being modulated responsive to said audio signals, the generator means being connected to the ring and tip terminals of the set whereby the signal of the radio frequency generator means is multiplexed on said lines and transmitting over said lines within a frequency band excluding said first frequency range; means for receiving at each of said telephone sets of modulated signal from the radio frequency generator means of another of said sets and producing a responsive audio paging signal at said speakers of said telephone sets; and a sensing means at each of said telephone sets for sensing the ambient background noise level at said telephone sets for a predetermined time increment before receiving said paging signals, a means for triggering a laching means for enabling the transmitting audio signals of one of said telephone sets which is the first to be triggered whenever the voltage level following said paging signal exceeds said ambient background noise level after said predetermined time increment; a means for disabling the transmitting audio enabling and receiving audio signals for other telephone sets following the enabling of the first telephone set transmitting audio signal; and a means for disabling all the answering transmitting and receiving audio signals when the originating transmitting audio signal is terminated.