Larry N8KU originally posted November 2013 [updated 9-1-2024]
“High SWR is bad…antennas that show high SWR are inefficient and do not radiate well. So if my SWR is bad, no one will hear me.”
Your antenna does not have an SWR. The feedline does.
An antenna’s efficiency is determined by the ratio of its radiation resistance to its total input resistance. What goes in, should come out. You can have a great antenna connected to a terrible feedline – it might be way too long, or full of water.
I would rather have a great feedline (with the greatest being a balanced one) connected to a terrible antenna – because I can still tune it to match, and it will radiate.
A dummy load has an SWR of 1.0 and it hardly radiates at all. A short vertical antenna with a radiation resistance of 0.1 ohm and a loss resistance of 49.9 ohms radiates only 0.2% of its input power, but has an SWR of 1.0.
What does SWR really mean?
SWR has very little to do with how well the other station hears you. It is only a reflection (!) of how happy your transmitter might be. Unhappy transmitters will not work hard. Unhappy transmitters may even overheat and be damaged. That “reflected” power may also try to go somewhere it doesn’t belong – like your computer, your TV, or anything else with long pieces of wire attached to it.
I often use antennas on completely different bands than those they were designed for, or resonate on, with the panel on the transceiver flashing “warning – high SWR.” (In that case I do dial down the power a bit, just in case.) I have worked many rare ones that way.
My favorite examples are those mobile antennas for HF – manufacturers fall all over themselves trying to convince you that their 6′ long antenna is going to be great on 75-meter sideband. As Scotty would say, “ya cannae change the laws of physics, Cap’n!”
What you then have is (relatively speaking) either a very tiny antenna, or a large dummy load.
Don’t get me wrong – you can make contacts with a dummy load. I’ve done it. I’ve made contacts loading up a slinky too, but I don’t recommend them for everyday use.