🔍 Key Concepts

• Radio frequency bands used in marine communications (VLF, LF, MF, HF, VHF) • Difference between frequency in kHz and types of modulation (SSB, FM) • Typical frequency ranges used for maritime SSB voice vs. very low frequency systems

💭 Think About

• First, separate the choices that are specific frequency ranges from those that are types of modulation. What is the question actually asking for? • Think about where very low frequency (VLF) and low frequency (LF) sit on the radio spectrum compared to common marine HF and VHF channels. • Consider whether modern marine communication systems normally operate below 30 kHz, and if so, what they are mainly used for.

✅ Before You Answer

• Check the numerical order of frequencies given (1 kHz, 5 kHz, 15 kHz, HF/VHF voice) and which are truly the lowest on the spectrum. • Verify whether SSB voice is a modulation method covering a band of frequencies, rather than a specific frequency value. • Confirm if kHz values below 30 kHz are realistic and currently used in certain specialized long‑range maritime or navigation systems.