Ham Radio General Class Practice Test

If the SWR on an antenna feed line is 5 to 1, and a matching network at the transmitter end of the feed line is adjusted to 1 to 1 SWR, what is the resulting SWR on the feed line?

1. 1 to 1

2. 5 to 1

3. Between 1 to 1 and 5 to 1 depending on the characteristic impedance of the line

4. Between 1 to 1 and 5 to 1 depending on the reflected power at the transmitter

The correct answer is: 5 to 1

When a matching network is placed at the transmitter end of the feed line and is successfully adjusted to achieve a 1 to 1 SWR, this indicates that the network is efficiently matching the load (the antenna) to the line. However, the SWR that exists at the antenna feed point before this matching network is still 5 to 1. The critical point to understand is that the condition at the transmitter end is a result of the work done by the matching network. The SWR of 5 to 1 indicates that there is a significant mismatch between the feed line and the antenna, leading to considerable reflected power. This mismatch does not magically change over the length of the feed line; rather, the SWR reflected back from the load remains at 5 to 1 until it is transformed by the matching network. Thus, when the feed line experiences the 5 to 1 mismatch at the load (antennas), this condition does not change simply because a matching network is implemented at the transmitter end. As a result, while the immediate load at the transmitter end achieves a perfect match of 1 to 1 due to the matching network, the reflected waves and their interactions along the feed line maintain the original SWR characteristic of