Techniques for real-time HF channel measurement and optimum data transmission

The time variability of path loss, noise, interference, and dispersion which characterize an HF channel can be overcome by adding three elements to the conventional communication system: (1) a transmission test set; (2) an interference monitor; and (3) high order time diversity. The transmission test set continuously monitors the circuit loss and multipath, 3-30 MHz. The optimum operating frequency is obvious from the test set display, but the specific frequency must be selected from among the allocated choices on the basis of interference. The interference monitor measures and stores the percentage occupancy of all HF channels and the operating frequency is chosen from the monitor display. Although a clear, propagating frequency is selected, noise and fading cause data transmission errors; the most effective solution is high order time diversity.