ARRL Technician Practice Exam

What generally occurs as the frequency of a signal passing through coaxial cable is increased?

1. The loss decreases

2. The impedance decreases

3. The loss increases

4. The bandwidth increases

The correct answer is: The loss increases

As the frequency of a signal passing through coaxial cable is increased, the loss typically increases due to several factors inherent to the properties of the cable and the phenomenon of signal transmission. Coaxial cable loss arises primarily from two sources: resistive loss from the conductor materials and dielectric loss within the insulating material surrounding the conductor. At higher frequencies, the skin effect causes the current to concentrate near the surface of the conductors, which increases the effective resistance and contributes to higher losses. Additionally, dielectric losses increase with frequency due to the material properties, leading to more energy being dissipated as heat. Therefore, it is expected that as the frequency rises, the overall loss of the signal in the coaxial cable will also increase. The other factors like impedance and bandwidth behave differently with frequency. The characteristic impedance of coaxial cable remains constant regardless of the frequency within its specified range. While bandwidth does increase, this is not universally applicable to the overall performance of signal transmission in this context; it does not contribute to the loss characteristics you would observe. Thus, while bandwidth can relate to usable frequencies of a signal, it does not negate the increase in loss observed with higher frequencies in coaxial cable.