System for simultaneous analog and digital communications over an analog channel

A system for simultaneously communicating an analog voice signal and a voiceband digital signal from a sender to a receiver comprising:

• (a) means, at the sender, for filtering from a voice signal to be transmitted those frequency components used to construct a digital signal to be transmitted resulting in a first interim signal, removal of said frequency components being for the purpose of preventing errors which could be caused by the presence of voice components in the digital signal,
• (b) means, at the sender, for producing a second interim signal comprising the sum of the first interim signal and the digital signal,
• (c) means, at the sender, for transmitting the second interim signal,
• (d) means, at the receiver, for receiving the second interim signal,
• (e) means, at the receiver, for filtering from the received second interim signal those frequency components used to construct the digital signal,
• (f) selectable means, at the sender, for bypassing the means at the sender for filtering, the second interim signal comprising the voice signal whenever said selectable means is selected,
• (g) selectable means, at the receiver, for bypassing the means at the receiver for filtering,
• (h) means, at the sender, for transmitting a first signal as a forewarning to the receiver that a digital signal is forthcoming,
• (i) means, at the receiver, for transmitting back to the sender a second signal in response to the first signal as an acknowledgement of receipt of the first signal,
• (j) means, at the receiver, for de-selecting the bypass means at the receiver in response to the first signal, and
• (k) means, at the sender, for de-selecting the bypass means at the sender in response to the second signal.

In a communication channel over which a sender transmits analog voice signals and from time to time sends voiceband digital signals having a predetermined frequency construct to a receiver, each transmission of a digital signal being initiated by an acknowledgement signal transmitted from the receiver to the sender in response to an alert signal transmitted from the sender to the receiver, the alert signal being indicative that a digital signal is forthcoming, a system by which the sender can simultaneously transmit voice signals and digital signals comprising:

• (a) means, at the sender and having an input, for transmitting a signal at its input over said channel;
• (b) means, at the sender and having an input, for combining a signal at its input and the digital signal to produce a combined signal, and for communicating the combined signal to the input of the means for transmitting;
• (c) a first signal path, at the sender, comprising means for filtering from a voice signal to be transmitted each frequency component of the predetermined frequency construct, and for communicating the filtered voice signal to the input of the means for combining;
• and
• (d) a second signal path, at the sender, by which the voice signal bypasses the first signal path and is communicated to the input of the means for combining;
• (e) means, at the sender, for selecting the first signal path for the voice signal, the second signal path being normally selected;
• (f) means, at the receiver, for receiving signals from said channel;
• (g) a first signal path, at the receiver, comprising means for filtering from a received signal each frequency component of the predetermined frequency construct;
• (h) a second signal path, at the receiver, by which a received signal bypasses the first signal path;
• (i) means, at the receiver and at least partially responsive to an alert signal from the sender, for selecting the first signal path for the received signal, the second signal path being normally selected;
• and
• (j) means, at the receiver, for transmitting an acknowledgment signal over the channel to the sender in response to an alert signal from the sender.