Ham Radio General Class Practice Test

What is the characteristic impedance of flat ribbon TV type twinlead?

1. 50 ohms

2. 75 ohms

3. 100 ohms

4. 300 ohms

The correct answer is: 300 ohms

Flat ribbon TV type twinlead has a characteristic impedance of 300 ohms. This type of cable is often used in television antenna installations and is designed to efficiently carry radio frequency (RF) signals. The impedance value is crucial in matching the antenna to the transmission line and the receiver to minimize signal reflections and power loss. In contrast, other types of cables, such as coaxial cables, typically have lower characteristic impedances, such as 50 ohms used for many RF applications in ham radio, or 75 ohms which is commonly used in domestic television systems and cable TV installations. The use of 300 ohm twinlead in antennas is particularly beneficial when connecting antennas that are designed for high-impedance feeds, making it suitable for applications in ham radio where efficient signal transmission is important. This makes the correct answer relevant to understanding how different types of cables interact within radio frequency systems.