Ham Amateur Radio Technician Practice Exam

What standing wave ratio results from connecting a 50-ohm feed line to a 10-ohm resistive load?

1. 2:1

2. 3:1

3. 4:1

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 transmission line. It is calculated based on the impedance of the transmission line and the load connected to it. When connecting a 50-ohm feed line to a 10-ohm resistive load, the calculation of the SWR can be done using the formula: \[ SWR = \frac{Z_L + Z_0}{Z_L - Z_0} \] where \( Z_L \) is the load impedance (10 ohms) and \( Z_0 \) is the characteristic impedance of the feed line (50 ohms). Substituting the values in: \[ SWR = \frac{10 + 50}{10 - 50} = \frac{60}{-40} = -1.5 \] However, since we are dealing with magnitudes, we take the absolute value of the negative term: \[ SWR = \frac{60}{40} = 1.5 \] This value still does not represent the SWR in the expected form. The correct formula involves more direct calculations to finalize: You can also calculate SWR by using the relationship that when the load impedance is