Spectral Analysis and Implementation of Duobinary FSK Systems Working at High Bit Rates

A new modulation technique for nonperiodic data is presented. Binary data, coded by means of the duobinary technique, modulate a voltage controlled oscillator (VCO). The system has a very simple structure and is capable of transmitting data having a variable bit rate about twice the carrier (VCO) frequency. The resulting spectrum, centered around the VCO frequency, could be as narrow as 0.3 times the bit rate. Telephone line tests show that this technique offers a promising low-cost solution to voice-grade modems.