A computer-controlled, coded-pulse, step frequency, oblique sounder has been designed to probe the HF radio communication channel to a bandwidth of 1 MHz. The instrument monitors the complex pulse response of the channel over an extended period of time thus permitting simultaneous observation of the time and frequency behavior of the channel. A coherent time history presentation of the wide band data permits unequivocal identification of individual modes in situations involving several partially overlapping modes. Channel instantaneous bandwidth and mode Doppler shift can be estimated by inspection of the pulse response time history curves. Data presentation in the wide band time history format is also very informative in the description of signal fluctuation phenomena and in understanding their underlying causes. Measurements have been made over a short-baseline (126 km), mid-latitude path between an island off the southern California coast and the mainland. The response of the one-hop F2 layer sky wave mode to a 1-μs probing pulse is used to illustrate the unique capabilities of this instrument and the unusual effects that are observed with a high-resolution probing pulse.