SWR Power Loss Calculator

System Efficiency is Power to Antenna divided by Transmit Power, and both the reflected-power fraction (driven by SWR) and the extra feedline loss (driven by SWR and Matched Feedline Loss) are proportional to whatever power you put in -- so Transmit Power cancels out of the ratio entirely. A 100-watt radio and a 1500-watt radio at the same SWR and feedline loss see the identical percentage efficiency, even though the higher-power radio reflects far more raw wattage.

At a 2:1 SWR, the reflection coefficient Gamma works out to about 0.333, and Power Reflected (Gamma squared times Transmit Power) is roughly 11% of your transmit power -- meaning about 89% is still forwarded toward the antenna before accounting for the additional feedline loss SWR introduces on top of that. Most operators consider 2:1 a reasonably tolerable mismatch, though it's still worth tuning out if you can.

SWR increases feedline loss beyond the cable's normal matched-line rating, via a multiplier applied to Matched Feedline Loss -- and Matched Feedline Loss itself scales with cable length. So the same SWR mismatch adds a bigger absolute loss penalty on a long run of coax than on a short jumper, which is why minimizing SWR matters even more as your feedline gets longer.

Safe for Rig flags whether SWR is at or below 3:1, a commonly cited threshold above which many amateur radio transceivers automatically fold back (reduce) their output power to protect the final amplifier stage from the increased reflected power. It's a general rule of thumb, though -- always check your specific transmitter's actual SWR tolerance in its manual rather than relying on this threshold alone.