A comparison is made of four different estimators, for estimating the sampled impulse-response (SIR) of an HF radio link that is designed for the transmission of analog speech signals. The particular application studied is the transmission of digital data at 4800 bit/s, employing a serial quadrature phase shift keyed (QPSK) signal with a carrier frequency of 1800 Hz. The HF radio link is modeled as having three different Rayleigh-fading paths (sky waves). System 1 is the conventional gradient (least mean square, or LMS) estimator while system 2 is the gradient estimator with degree-1 least-squares fading memory prediction. Systems 3 and 4 are novel and are developments of system 2. Results of computer simulation tests on the four different estimators are presented. >