🔍 Key Concepts

• GMDSS MF/HF equipment usually uses a specific antenna impedance standard • Coaxial cable types (RG-59, RG-6, RG-8, RG-179) have different characteristic impedances and typical applications • Matching the cable impedance to the transmitter/antenna system is critical to avoid power loss and reflections

💭 Think About

• What is the standard impedance for most marine MF/HF transmitters and antennas used for GMDSS? • Which one of the listed coax types is commonly used in radio transmitters where maximum power transfer and low loss at MF/HF are needed? • How would using a 72–75 ohm cable with equipment designed for a different impedance affect standing wave ratio (SWR) and efficiency?

✅ Before You Answer

• Identify the standard impedance (in ohms) for MF/HF marine radio equipment used in GMDSS • Check which option has that same characteristic impedance • Eliminate any coax types that are primarily known for TV/video or receive-only applications rather than high‑power MF/HF transmission