Tools · Feedline
Coax Loss Calculator
How much of your power actually reaches the antenna — matched loss, extra loss from SWR, and the SWR your radio really sees.
Cable type
Run length
ft
m
Frequency (MHz)
Transmit power (W)
SWR at the antenna
Enter your cable run to see the losses.
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Power reaching the antenna
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Loss compounds with frequency.
A run that's fine on 80m can eat half your signal on 70cm — always check at the highest band you use.
SWR hurts more on lossy cable.
Reflected power makes extra round trips through the line, so high SWR + long thin coax is the worst combination.
Your radio sees a better SWR than the antenna's.
Line loss masks the mismatch — a "great SWR" at the rig can hide a poor antenna match.
Figures are typical published values per 100 ft at 20°C; check your cable's datasheet for exact numbers. Connectors add roughly 0.1 dB each.
3 dB of loss = half your power. 1 dB ≈ 21% gone.