🔍 Key Concepts

• HF propagation and how it depends on the ionosphere • The idea of short rules of propagation selection (time of day, frequency band, distance) • How Optimum Usable Frequency (OUF/OUF predictions) are used in practice vs. operator judgment

💭 Think About

• Think about how predictable HF propagation is over the short term: can past successful contacts on a band be useful, or is the ionosphere too random? • Consider what a practical GMDSS operator at sea actually does before transmitting: do they just trust the radio’s calculations, or do they combine tools with operating experience? • Which option reflects both good radio practice and understanding of HF propagation, rather than trial-and-error or blind trust?

✅ Before You Answer

• Identify which options encourage using basic propagation rules (time of day, frequency, range) instead of random band-hopping. • Check which choice balances use of equipment features with operator knowledge and previous experience. • Eliminate any answer that suggests completely ignoring known propagation rules or completely ignoring helpful equipment calculations without good reason.