Ham Radio General Class Practice Test

What is the primary purpose of a balun in an antenna system?

1. To improve the impedance matching

2. To increase the signal gain

3. To filter out unwanted frequencies

4. To provide weather protection

The correct answer is: To improve the impedance matching

A balun, which is short for balanced-to-unbalanced transformer, primarily serves to improve impedance matching in an antenna system. In many cases, antennas are designed to operate in a balanced mode (where current distribution is even across the antenna feed), while most transmission lines (like coaxial cables) are unbalanced. The balun allows for a seamless transition between these two types by transforming the impedance encountered at the antenna feed point to match that of the transmission line. This impedance matching is crucial for maximizing power transfer from the transmitter to the antenna and minimizing reflections that can lead to standing waves on the transmission line, which can degrade performance. By ensuring that the impedance seen by the antenna is appropriately matched to the feeder, the balun helps to enhance the efficiency of the whole system. Other functions often attributed to baluns, such as filtering unwanted frequencies or providing weather protection, are typically not their primary roles. Instead, those purposes are more aligned with other components in the antenna system or protective measures installed separately.