Ham Radio General Class Practice Test

What happens to a feed line when the load impedance is very different from the characteristic impedance of the line?

1. Rejection of all transmitted power

2. Reflected power and standing waves increase

3. The line becomes perfectly matched

4. Load power increases

The correct answer is: Reflected power and standing waves increase

When the load impedance is very different from the characteristic impedance of the transmission line, the result is an increase in reflected power and standing waves. This phenomenon occurs due to the mismatch between the load and the transmission line's impedance. The characteristic impedance of a feed line is designed to match the impedance of the load for optimal power transfer. When there is a significant mismatch, a portion of the transmitted power is reflected back towards the source instead of being absorbed by the load. This reflection leads to the formation of standing waves along the transmission line, which can degrade the efficiency of the system. The increased standing waves indicate that there are points along the line where the voltage and current are not in phase, resulting in inefficient transmission of power. In summary, a severe mismatch between load impedance and the line's characteristic impedance results in higher levels of reflected power and the development of standing waves, which means that not all of the transmitted power is effectively utilized.