Data modems with automatic equalization, drop-out detection and data

Abstract

Disclosed is an automatic data communication system having communicating modems equipped with automatic equalizers. The equalizers respond to a first long equalization sequence automatically transmitted from another modem. In response to that long equalization sequence, the equalizer starts from a preset non-equalized condition and assumes a fully equalized condition. That equalized modem is also capable of automatically transmitting its own long equalization sequence to the other modem. Thereafter, second short equalization sequences are employed at the receiving modems to enable a memory storage associated with the automatic equalizers. The memory stores, in response to the long equalization sequence, signals which are indicative of the fully equalized condition. Accordingly, the equalizers do not have to start from a non-equalized condition for each new data message unless a dramatic distortion occurs. If such distortion does occur, it is automatically detected and long equalization sequences are again employed to fully re-equalize. The disclosed modems have detection means for automatically distinguishing between equalization sequences, line drop-outs, and data echoes.