Which of the following direct, fused power connections would be the best for a 100-watt HF mobile installation?

Connecting directly to the vehicle's battery using heavy-gauge wire is the best practice for high-power (100-watt) mobile HF installations. The battery acts as a massive capacitor, which is highly effective at filtering out alternator whine, ignition noise, and other electrical transients before they reach your radio. Heavy-gauge wire is absolutely necessary to handle the high current demands of a 100-watt transmitter, which can draw upwards of 20 to 25 amps on transmit. Proper thickness minimizes voltage drop, ensuring the radio receives the full 13.8 volts it needs to operate correctly. Connecting directly to the alternator is a poor choice because it exposes the radio to severe voltage spikes and electrical noise. Additionally, balanced transmission line is designed for routing RF signals to an antenna, not for carrying DC power.