Amateur Radio’s Holy Grail
Summer is a good time to do a little myth busting about the topic hams love to chat about; Voltage Standing Wave Ratio, VSWR, often abbreviated as SWR. This month’s column was inspired by the articles written by Walter Maxwell, W2DU (SK).
A low SWR means an efficient antenna
The SWR only tells you how well the antenna system including feedline is matched to the transmitter. It tells you nothing about how well the antenna radiates electromagnetic energy. A dummy test load or “cantenna”, has a near perfect VSWR and it’s the worst antenna out there. Many antenna/feedline systems with SWR of 3:1 radiate extremely well. Efficiency depends on radiation resistance, conductor losses, ground losses, and antenna gain. An SWR of 2:1 reflects 11% of transmitted energy back down the feedline, 3:1 VSWR reflects 25%, but most of that is re‑radiated when it reflects back toward the antenna. None of that would be noticeable when considering one S-unit presents 6 dB or a factor of 4 of signal power.
High SWR wastes power
This is one of the most persistent misunderstandings. When an antenna is mismatched, some power reflects toward the transmitter but with a lowloss feedline, that power does not disappear. It bounces back and forth between transmitter and antenna until most of it is eventually radiated by the antenna. Some energy is lost as heat in the feedline and that loss during these round trips is an important factor. On HF bands with a good coax cable or a ladder line, that loss is small. A 3:1 VSWR does not mean you’re losing 25% of your power. Most of that 25% reflected energy still gets out.
High SWR will damage my rig
Modern radios include SWR protection, power foldback, and thermal safeguards. Most rigs built in this century easily tolerate 3:1 and even higher SWR. The transceiver merely reduces output power to protect the output transistors (finals) in the RF power amplifier. However, older transceivers from the later half of the 20th century, including hybrid rigs with vacuum tube finals, can be stressed by high SWR because they lack modern protection circuitry. A little care is needed when operating those ancient rigs at their rated power.
A tuner fixes my antenna
A tuner doesn’t fix anything at the antenna. It simply makes the transmitter happy by presenting it approximately 50ohm impedance. The antenna system still has the same losses and radiation characteristics it had before tuning. A tuner is just at an impedance matching circuit, and it’s much more useful when connected at the end of the feedline; at the antenna terminals.
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Last Updated on 2026-08-05 by Eve