A receiver capable of overcoming severe intersymbol interference and speedily tracking High-Frequency（HF） channel fading is presented. This receivre

combines the pree-qualization（PE） with the nearly maximum likelihood sequence estimation

uses square root Kalman algorithm to jointly regulate the PE and overall channel parameters. The computer simulation shows that nearly optimal error-rate performence can be achieved with this receiver structure for serial high-speed digital transmission on HF channels.