Understanding SWR by Example
Take the mystery and mystique out of standing wave ratio.
Darrin Walraven, K5DVW
“It sometimes seems that one of the most mysterious creatures in the world of Amateur Radio is standing wave ratio (SWR). I often hear on-air discussion of guys bragging about and comparing their SWR numbers as if it were a contest. There seems to be a relentless drive to achieve the most coveted 1:1 SWR at any cost. But why?
This article is written to help explain what SWR actually is, what makes it bad and when to worry about it. What is SWR? SWR is sometimes called VSWR, for voltage standing wave ratio, by the technical folks. Okay, but what does it really mean? The best way to easily understand SWR is by example. In the typical ham station setup, a transmitter is connected to a feed line, which is then connected to the antenna.
When you key the transmitter, it develops a radio frequency (RF) voltage on the transmission line input. The voltage travels down the feed line to the antenna at the other end and is called the forward wave. In some cases, part of the voltage is reflected at the antenna and propagates back down the line in the reverse direction toward the transmitter, much like a voice echoing off a distant cliff. SWR is a measure of what is happening to the forward and reverse voltage waveforms and how they compare in size. “
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