Ham Radio General Class Practice Test

Which of the following factors determine the characteristic impedance of a parallel conductor antenna feed line?

1. The distance between the centers of the conductors and the radius of the conductors

2. The distance between the centers of the conductors and the length of the line

3. The radius of the conductors and the frequency of the signal

4. The frequency of the signal and the length of the line

The correct answer is: The distance between the centers of the conductors and the radius of the conductors

The characteristic impedance of a parallel conductor antenna feed line is determined by the distance between the centers of the conductors and the radius of the conductors. This relationship arises from the capacitance and inductance of the feed line. When calculating impedance, the formula incorporates both the physical geometry of the conductors and their dimensions. The distance between the centers influences the capacitance per unit length, while the radius affects the inductance per unit length. Therefore, these two factors are crucial in defining the characteristic impedance, as they directly impact the electrical behavior of the transmission line. The other factors listed, such as the length of the line and frequency of the signal, while relevant in other contexts (like in the calculation of loss or changes in impedance due to frequency response), do not directly determine the characteristic impedance itself. The impedance remains a function of the physical attributes—primarily the spacing and size of the conductors—rather than these other aspects.