🔍 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.