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 10-ohm impedance?

1. 2:1

2. 50:1

3. 1:5

4. 5:1

The correct answer is: 5:1

The standing wave ratio (SWR) is a measure of the efficiency of power transmission in a radio frequency system and is determined by the impedance of the feed line and load. In this case, you have a 50-ohm feed line connected to a load with an impedance of 10 ohms. To understand why a SWR of 5:1 is the correct answer, you can use the formula for SWR, which is: SWR = (Z_load + Z_feed) / (Z_load - Z_feed) In this scenario: - Z_load (impedance of the load) = 10 ohms - Z_feed (impedance of the feed line) = 50 ohms When applying the values to the formula: SWR = (10 + 50) / (10 - 50) SWR = 60 / (-40) SWR = -1.5 (in magnitude, we only consider the absolute value) However, the above calculation has an issue with the sign notation. When we take absolute values of impedances in radio, we look at the reflection coefficient and the magnitude of mismatch which leads us to a simplified approximation based on reflection coefficient. Alternatively, a more straightforward way to calculate