Ham Amateur Radio Technician Practice Exam

What standing wave ratio results from connecting a 50-ohm feed line to a 200-ohm resistive load?

1. 2:1

2. 3:1

3. 4:1

4. 5:1

The correct answer is: 4:1

The standing wave ratio (SWR) is a measure of impedance matching between the transmission line and the load connected to it, which affects how much power is reflected back to the source rather than being transmitted to the load. In this scenario, we have a 50-ohm feed line connected to a 200-ohm resistive load. To calculate the SWR, we use the formula: \[ SWR = \frac{Z_L}{Z_0} + \frac{Z_0}{Z_L} \] where \(Z_L\) is the load impedance and \(Z_0\) is the characteristic impedance of the feed line. Substituting the given values: \[ SWR = \frac{200}{50} + \frac{50}{200} = 4 + 0.25 = 4.25 \] For practical purposes, the SWR is often rounded to a more convenient ratio. With a calculated value of 4.25, this roughly corresponds to a SWR of 4:1, indicating that when the load impedance differs significantly from the feed line's characteristic impedance, the standing wave ratio increases. This means that the correct answer reflects that higher impedance mismatch leads to