Ham Radio General Class Practice Test 2026 – Complete Exam Prep

Question: 1 / 545

What would be the SWR if you feed a vertical antenna that has a 25-ohm feed-point impedance with 50-ohm coaxial cable?

2:1

The Standing Wave Ratio (SWR) is a way to measure the match between the feedline and the load it is connected to, typically an antenna. To find the SWR based on the feed-point impedance of the antenna and the characteristic impedance of the feedline, you can use the following formula:

\[

\text{SWR} = \frac{Z_L + Z_0}{Z_L - Z_0}

\]

where \( Z_L \) is the load impedance (the antenna's feed-point impedance) and \( Z_0 \) is the characteristic impedance of the coaxial cable.

In this scenario, with a vertical antenna that has a 25-ohm feed-point impedance and feed with 50-ohm coaxial cable, the calculation becomes:

\[

\text{SWR} = \frac{25 + 50}{25 - 50} = \frac{75}{-25} = -3

\]

When simplifying, you only consider the absolute value for the purpose of SWR:

1. The numerator (25 + 50) = 75 ohms.

2. The denominator (25 - 50) = -25 ohms, but we take the absolute value, which

Get further explanation with Examzify DeepDiveBeta

2.5:1

1.25:1

You cannot determine SWR from impedance values

Next Question

Report this question

Download Ham Radio General Class Practice Test PDF Study Guide
Subscribe

Get the latest from Examzify

You can unsubscribe at any time. Read our privacy policy