Deep Dive: T4A01
The correct answer is D: 13.8 volts at 12 amperes. A typical 50-watt output mobile FM transceiver requires approximately 13.8 volts at 12 amperes for its power supply. This provides about 165 watts of input power (13.8V × 12A = 165.6W), which accounts for the transceiver's efficiency and overhead. Mobile transceivers are designed to operate from a vehicle's 12-volt electrical system, which typically provides around 13.8 volts when the engine is running (the alternator charges the battery to about 13.8V). A 50-watt output transceiver needs more input power than 50 watts because transceivers are not 100% efficient - some power is lost as heat. The 12-ampere current rating ensures adequate power delivery for the transceiver's needs, including receive operation and transmit at full power.
Why Other Answers Are Wrong
Option A: Incorrect. 24 volts is for some commercial systems, not typical mobile amateur transceivers which use 12-volt systems. Option B: Incorrect. 13.8 volts at 4 amperes provides only 55.2 watts, which is insufficient for a 50-watt transceiver with overhead and efficiency losses. Option C: Incorrect. 24 volts is not standard for mobile amateur equipment. Mobile amateurs use 12-volt (13.8V) systems.
Exam Tip
50W mobile = 13.8V at 12A. Remember: A typical 50-watt mobile transceiver needs approximately 13.8 volts at 12 amperes. This accounts for efficiency and provides adequate power.
Memory Aid
**5**0W **M**obile = **1**3.**8**V **1**2A (think '50M = 13.8V 12A')
Real-World Example
You're installing a 50-watt 2-meter mobile transceiver in your car. You connect it to a power supply that provides 13.8 volts (standard vehicle voltage when running) and can deliver 12 amperes. This gives you 165.6 watts of input power, which is more than enough for the 50-watt output plus receiver operation and efficiency losses. The transceiver operates reliably with this power supply rating.
Source & Coverage
Question Pool: 2022-2026 Question Pool
Subelement: T4A
Reference: FCC Part 97.313
Key Concepts
Verified Content
Question from the official FCC Technician Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the T4A topic.