Method of and apparatus for modulation of FSK carrier in a very narrow band

A communication system for transmitting and receiving an FSK carrier signal for communicating binary data, said communication system comprising:

• a circuit for receiving a binary data input signal, for generating a reference signal, and for generating a control signal having a first frequency and a second frequency in response to the binary data input signal;
• a modulator coupled to said circuit for phase reversal keying modulation of the reference signal with the control signal to create a carrier signal having a first carrier frequency and a second carrier frequency;
• a high order transmitter filter with a narrow bandwidth to filter the carrier signal for creating an FSK carrier signal with a narrow bandwidth which is applied to a transmission medium;
• a high order receiver filter with a narrow bandwidth for receiving and filtering the FSK carrier signal from the transmission medium;
• and
• a demodulation unit for processing the FSK carrier and generating a binary output data signal.

A method for generating and transmitting an FSK output signal with a narrow bandwidth, said method comprising the steps of:

• receiving a binary data signal;
• generating a control signal in response to said binary data signal, said control signal having a first frequency and a second frequency representing binary data;
• generating a reference signal;
• modulating said reference signal and said control signal by phase reversal keying to create a carrier signal;
• filtering said carrier signal with a high order filter having a narrow bandwidth to create a FSK carrier signal;
• and
• applying the FSK carrier to a transmission medium.

A method for generating, transmitting, and receiving an FSK output signal with a narrow bandwidth, said method comprising the steps of:

• receiving a binary data input signal;
• generating a control signal in response to said binary data input signal, said control signal having a first frequency and a second frequency representing binary data;
• generating a reference signal;
• modulating said reference signal and said control signal by phase reversal keying to create a carrier signal;
• filtering said carrier signal with a high order filter having a narrow bandwidth to create an FSK carrier signal;
• applying the FSK carrier to a transmission medium;
• receiving the FSK carrier from a transmission medium;
• filtering said FSK carrier signal with a high order filter having a narrow bandwidth;
• and
• demodulating said FSK carrier signal to generate a binary data output signal.