Ham Radio General Class Practice Test

What standing wave ratio will result from the connection of a 50-ohm feed line to a non-reactive load having a 200-ohm impedance?

1. 4:1

2. 1:4

3. 2:1

4. 1:2

The correct answer is: 4:1

The correct answer is a standing wave ratio (SWR) of 4:1. To understand why this is the case, it's essential to look at how SWR is calculated based on the characteristic impedance of the feed line and the load impedance. SWR is a measure of the efficiency of RF power transmission through a transmission line. It is defined using the formula: SWR = (1 + Γ) / (1 - Γ) where Γ (the reflection coefficient) can be calculated using the formula: Γ = (ZL - Z0) / (ZL + Z0) In this scenario, Z0 (the feed line impedance) is 50 ohms, and ZL (the load impedance) is 200 ohms. By substituting these values into the reflection coefficient formula: Γ = (200 ohms - 50 ohms) / (200 ohms + 50 ohms) Γ = 150 / 250 Γ = 0.6 Now, substituting this reflection coefficient into the SWR formula: SWR = (1 + 0.6) / (1 - 0.6) SWR = 1.6 / 0.4 SWR =