Traditional HF-radio
The military has been using high frequency (HF, 3 – 30 MHz) propagation for its features bending over the surface of earth especially when ground is well conducting. Navies have been using HF, particularly for surface propagation as the wave bends far beyond the visual horizon. Ground and special forces have been using the ionosphere reflection to extend the connection even further beyond the radio horizon.Traditionally HF connection has been used to transfer information with Morse code (CW) and voice (AM). Channel distribution has been following basic 300 Hz spacing. With advanced modems, the throughput can reach up to 19 Kbps without forward error correction. The challenging propagation planning has been replaced by automatic link establishment (ALE) . Currently, it can establish a new link within 10 seconds. Automated HF communications have become available even without profound and extended training. It used to take three months of continuous training to produce an HF operator team from musical people that could provide 60/60 marks per minute throughput with Morse code.
The specifications for traditional HF radio are captured from https://www.thalesgroup.com/en/worldwide/defence/hf-3000-skyfst
Modern cognitive HF-radio
The most modern way of utilizing HF communications includes spreading the transmission over the whole band from 3 MHz to 30 MHz. This provides below the Noise level modulation at amplitude dimension but can be received through decoding. Spreading the transmission also provides up to 153 Kbps data transmission, which applies to Internet Protocol (IP) connections. When spread spectrum is used together with 3rd generation Automatic Link Establishment, the modern cognitive HF radio is born. The artificial intelligence ensures link establishment within 500 milliseconds, adjusts to volatile channel conditions, and transmits IP-packages avoiding detection by traditional signals intelligence.
The specifications for modern HF radio are captured from http://www.kyynel.net/public-safety-security-defense.html
