Conferencing apparatus and methods for a frequency division multiplex communications system

In a frequency division multiplex communication system of the type having a plurality of subscriber stations each including a first transmitter and a first receiver coupled to a transmission path, with said transmitter and receiver having respectively an assigned frequency for transmitting and receiving, with said frequencies being related by a fixed frequency separation corresponding to the differenced in transmitter and receiver intermediate frequencies, mixer means for mixing a predetermined frequency with said intermediate frequencies to derive an independent sideband signal comprising an upper and a lower sidebands such that one sideband thereof contains communication information and the other sideband contains signaling data, filter means at said transmitter and said receiver having a bandpass of approximately twice the difference in frequency between said transmitter intermediate frequency and said receiver intermediate frequency, for rejecting undesired mixing products such that the desired sideband signal is selected, means for coupling said independent signal onto said transmission path, with said path coupled to a common reference frequency means to permit simultaneous signaling and communications between said subscriber stations, the combination therewith of conferencing apparatus at each subscriber station to enable a first plurality of subscribers to communicate in a conference mode without feedback oscillations, each of said stations further comprising:

• a second transmitter and a second receiver coupled to said transmission path and adapted to transmit and receive respectively a first transmitting frequency assigned to another subscriber and a first receiving frequency assigned to said other subscriber,
• memory means at said each subscriber station to store therein data indicative of transmit and receive frequencies at which said each subscriber station is operating with, apart from those respectively assigned thereto,
• means associated with one of said stations for transmitting said stored frequencies to any other subscriber station, to enable that another station to select said frequencies associated with said another subscriber, whereby any number of subscribers can communicate in a conference mode with said another subscriber being the nexus of said conference as having all subscribers transmitting and receiving on said frequencies assigned to said nexus subscriber.

A method for conferencing a plurality of subscribers in a frequency division multiplex system, comprising the steps of:

• coupling a plurality of subscribers to a transmission path, each subscriber having paired assigned transmitting and receiving frequencies, with each pair related by a fixed frequency separation being the difference in intermediate frequencies used in generating of the transmitting and receiving frequencies,
• mixing a synthesized frequency with said intermediate frequencies to derive an independent sideband signal such that one sideband thereof contains communication information and the other signaling information,
• filtering undesired mixing products to propagate any desired upper and lower sideband signals,
• coupling a common reference frequency to said transmission path, together with said independent sideband signals to allow any subscriber to communicate with another,
• storing at one subscriber location any selected, transmitted and received frequencies different from those assigned to said subscriber, and
• transmitting said stored frequencies to any requesting subscriber to enable said requesting subscriber to tune to said selected different frequencies as stored.

A method for conferencing a plurality of subscribers in a multiplex communication system comprising the steps of:

• coupling a plurality of subscribers to a common transmission path,
• connecting at least two of said subscribers via said path to enable communication therebetween,
• storing in a memory at one of said subscriber locations the assigned transmitting and receiving frequencies indicative of the location of said other subscriber,
• transmitting said frequencies as stored to any other subscriber calling said one subscriber, to enable said calling subscriber to call said other subscriber,
• connecting said calling subscriber to said other subscriber.