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The benefits of using high frequency (HF) circuits for both long-range beyond line of sight (BLOS) and short-range near vertical incidence skywave (NVIS) military applications are well documented. STANAG 4538 specifies an automated HF system that incorporates robust waveforms and protocols with the aim of providing faster link establishment and higher message throughputs under a variety of channel conditions. Under the auspices of the. NATO BLOS Communication WG, international trials have evaluated the link establishment and data link performance of S4538. Comparisons have been made with existing technologies such as MS-ALE and FS-1052. The testing has shown that S4538 offers a considerable improvement over MS-ALE in terms of increasing communications availability and decreasing LSU times. S4538 was also shown to be more reliable under poor channel conditions, such as those prevalent in the tactical environment. The operation of both point-to-point (PTP) and point-to-multipoint (PTM) protocols have been observed. Furthermore, the benefits of using RTCE information from sounding (or previous successful communications) has been observed.