Ham Radio General Class Test 2025 – 400 Free Practice Questions to Pass the Exam

Question: 1 / 545

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?

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 =

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1:4

2:1

1:2

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