ARRL Technician Practice Exam

What is the impedance of the most commonly used coaxial cable in typical amateur radio installations?

1. 75 ohms

2. 50 ohms

3. 100 ohms

4. 600 ohms

The correct answer is: 50 ohms

The impedance of the most commonly used coaxial cable in amateur radio installations is 50 ohms. This specific impedance is widely utilized because it strikes a balance between power handling capability and loss. In radio frequency (RF) applications, 50-ohm coax helps minimize signal loss while maintaining a good match with most RF power amplifiers and antennas found in amateur radio setups. Using 50-ohm coaxial cable allows for better efficiency in transmitting radio signals, ensuring maximum power is delivered to the antenna with minimal reflections back to the transmitter. Impedance mismatches can lead to increased standing wave ratios (SWR) which can result in signal loss and potential damage to transmitter components. While there are other impedances, such as 75 ohms commonly found in television coaxial cables, and other higher impedances that may have specific applications, 50 ohms remains the standard in amateur radio due to its performance characteristics across a wide range of frequencies used in the hobby. This makes it the appropriate choice for most amateurs looking to establish reliable communication.