Ham Radio General Class Practice Test

In a log periodic antenna, how does the spacing of the elements change?

1. Constant spacing across all elements

2. Increases or decreases linearly

3. Varies sinusoidally

4. Increases logarithmically along the boom

The correct answer is: Increases logarithmically along the boom

In a log periodic antenna, the spacing between the elements increases logarithmically along the boom. This design allows the antenna to operate effectively over a wide range of frequencies. The log periodic structure consists of a series of dipole elements that are progressively longer and spaced more widely as one moves along the boom. The logarithmic spacing is critical because it allows the antenna to maintain a consistent impedance across its operating bandwidth. As frequencies increase, the resonance of each element aligns with the transmission or receiving frequencies closely related to their length and spacing, which contributes to the antenna's ability to perform well over a broad spectrum. Other options do not accurately describe how the spacing changes in a log periodic antenna. Constant spacing would not provide the necessary impedance matching across frequencies, while linear or sinusoidal variations do not reflect the specific growth pattern that characterizes log periodic designs. The logarithmic increase is essential for achieving the intended performance and frequency capabilities of this type of antenna.