Ham Radio General Class Practice Test

Why is it best NOT to draw the DC power for a 100-watt HF transceiver from an automobile's auxiliary power socket?

1. The socket is not wired with an RF-shielded power cable

2. The socket's wiring may be inadequate for the current being drawn by the transceiver

3. The DC polarity of the socket is reversed from the polarity of modern HF transceivers

4. Drawing more than 50 watts from this socket could cause the engine to overheat

The correct answer is: The socket's wiring may be inadequate for the current being drawn by the transceiver

Drawing DC power for a 100-watt HF transceiver from an automobile's auxiliary power socket is best avoided primarily because the socket's wiring may be inadequate for the current being drawn by the transceiver. Automobile auxiliary power sockets are typically designed for low-current loads, like powering small electronic devices or charging smartphones. They are often wired with lighter gauge wire, which may not be capable of safely carrying the high current that a 100-watt transceiver requires. When a transceiver operates at 100 watts, the current draw can exceed 8 amps at 12 volts. If the wiring is not sufficient to handle this current, it can lead to overheating, voltage drops, or even damage to the vehicle's electrical system. Ensuring that the power supply is adequate for the load is crucial for safe and optimal operation of the equipment. While the other options may present potential issues, the inadequate wiring is the primary concern when attempting to draw a significant amount of power from an auxiliary socket in a vehicle.