High frequency: Narrowband transmissions and COM I NT may be poised for a comeback

摘要

• HF radio appears to be enjoying a renaissance as it can serve as a satcom backup • COMINT professionals could be challenged to address narrowband HF transmissions Transmitting across a waveband of 3-30 MHz, high-frequency (HF) transmissions can attain intercontinental ranges using so-called 'skywave' transmissions that employ an elegantly simple principle. These transmissions use the ionosphere, an atmospheric layer about 80 km (50 miles) to 1,000 km above the earth, in which ionisation acts as a natural antenna. HF transmissions can 'bounce' off this layer and obviate the line-of-sight range limitations of other HF transmissions.