A Vestigial-Sideband, Phase-Reversal Data Transmission System
D.L. Critchlow, Robert H. Dennard, E. Hopner · IBM Journal of Research and Development · 1964
A new method of carrier retrieval is described for a suppressed-carrier, vestigial-sideband data transmission system. Tests over voice grade telephone lines indicate that operation at 3000 bits per second (in some cases, 3600 bps) can be obtained reliably over private lines with simple adjustable equalization, whereas fixed compromise equalization will allow speeds up to 2400 bps over a large percentage of lines in the switched network. The possibility of higher speed operation using a multilevel data signal is demonstrated by tests at 6000 and 8000 bps over a carefully equalized private line.