Ham Radio General Class Practice Test

What are the typical characteristic impedances of coaxial cables used for antenna feed lines at amateur stations?

1. 25 and 30 ohms

2. 50 and 75 ohms

3. 80 and 100 ohms

4. 500 and 750 ohms

The correct answer is: 50 and 75 ohms

The typical characteristic impedances of coaxial cables used for antenna feed lines in amateur radio are 50 and 75 ohms. The 50-ohm coax is commonly used for transmitting applications, particularly in ham radio, due to its ability to minimize signal loss in the RF spectrum. This makes it ideal for feed lines connecting transmitters and receivers to antennas. On the other hand, the 75-ohm coax is often used for receiving applications and television signals, where lower loss is important over longer distances. Both values are standard and widely available in the market, which makes them practical choices for amateurs setting up their equipment. When considering the other options, 25 and 30 ohms are not commonly utilized for coaxial applications in amateur radio, and there are much fewer options in those impedance ranges. The 80 and 100 ohm options are generally associated with balanced feed lines, like twisted pairs, rather than coaxial lines. Additionally, the values of 500 and 750 ohms are not used in standard coaxial applications for amateur radio, making them impractical in this context.