HF communications standards, created by the US Govern-ment, NATO, and other organizations, greatly influence the design of HF equipment and systems. These standards apply to equipment specifications, waveform design, communication protocols, and computer control. They serve to:

• Ensure interoperability among systems used by different organizations.

• Reduce ambiguous descriptions of equipment and systems by providing a common language in equipment specifications and in defining the operating environment.

• Allow more accurate comparison between different equip-ment by defining test conditions.

A summary of some of the most important HF radio communi-cation
standards are:

• Federal Standard 1045A, HF Radio Automatic Link Establishment. Specifies automated radio features, including frequency scanning, selective calling, ALE, LQA, and sounding, which ensure interoperability of radio systems.

• Federal Standard 1052, HF Radio Modems. Defines design objectives for data modems and performance requirements for a data link protocol compatible with the ALE standards estab-lished by FED-STD 1045A.

• MIL-STD-188-100 Notice 1, Common Long Haul and Tactical Communications System Technical Standards. Specifies requirements for interconnecting long-haul and tactical systems for voice and data service.

• MIL-STD-188-110A, Interoperability and Performance Standards for Data Modems. Establishes requirements and design objectives that ensure specified levels of performance of voice-frequency data modems used in communications systems.

• MIL-STD-188-141A, Interoperability and Performance Standards for Medium- and High-Frequency Radio Equipment. Establishes requirements and design objectives that ensure interoperability and specified levels of perfor-mance for HF radio equipment. Includes details about imple-menting
ALE systems, waveforms, signal structures, protocols, and LQA.

• NATO STANAG 4285, Characteristics of 1200/2400/3600 bps Single-Tone Modulators/Demodulators for HF Radio Links. Defines the parameters that ensure interoperability between single-tone modems designed for communicating via HF radio links at bit rates of 1200, 2400, or 3600 bps.

• NATO STANAG 4529, Modification of NATO STANAG 4285 to deliver data and voice in 1240 Hz bandwidth.