Feedline Loss Calculator

Tells you how much of your transmitter power actually reaches the antenna — and how much is heating up the dielectric in your coax. Pick your cable, your run length, your band, and your TX power. The numbers update as you go.

How To Read The Result

Line Loss (dB). Under 1.5 dB across your run is excellent. Between 1.5 and 3.0 dB is acceptable for most stations. Above 3.0 dB you are losing more than half your power before it leaves the shack — time to rethink the cable or shorten the run.

Watts at Antenna. The number that actually matters. If you're running 100W from the rig and only 50W reaches the antenna, you have effectively cut your station in half. Doubling power to compensate (100W to 200W) costs significantly more than upgrading to better coax.

Watts Lost as Heat. This power is gone — converted to heat in the dielectric and never radiated. It's the cost of running the cable you chose at the band you chose for the length you chose. Sometimes that cost is acceptable. Knowing the number is the first step.

Pick The Right Coax The First Time

The single most important variable in the result above is the cable you chose. Larger diameter coax = lower loss. The cost difference between RG-8X and LMR-400 on a 100-foot run is modest. The dB difference is significant on the higher bands. RG-213 is included above because it remains one of the most popular coax types in amateur service — useful as a reference point against the lower-loss LMR family.

A Note On 450Ω Ladder Line

Ladder line is the lowest-loss feedline option on this list and the oldest. Used correctly — with a balanced tuner at the shack — it outperforms every coax type shown here by a wide margin. Three things to know before you choose it:

It cannot be buried. Ladder line must run in open air. If it must cross a span where coax would normally be buried, it has to run through large-diameter open-air conduit so the conductors stay surrounded by air, not soil or insulation.

It is weather-sensitive. Rain, ice, and accumulated dirt on the conductors all change its impedance. Performance is best when the line is clean and dry, and operators in wet climates often see day-to-day variation that coax users do not.

The dB figures shown are matched-line loss. Ladder line is typically operated at high SWR by design — that's part of why it works so well with a balanced tuner feeding a doublet or VDA. Actual loss in service depends on the load impedance and can be higher than the matched-line number on the screen. For the full physics, see the Feedline Physics page.

If you want the long-form on feedline behavior, SWR-loss interaction, and common-mode noise on receive, the deep dive lives on the Signal Lab. If you want a turnkey feedline system matched to a Greyline VDA, the kits are spec'd to remove the guesswork.

About The Numbers

The loss values used in this calculator are derived from manufacturer specifications and field measurements for each cable type at standard HF amateur bands. Calculations assume a matched (low-SWR) load; actual loss will be higher in installations with significant SWR on the line, and the effect is most pronounced on ladder line, which is normally operated mismatched by design. For a deeper treatment of SWR-loss interaction and feedline behavior generally, see Walter Maxwell W2DU's Reflections III — cited in the Greyline Authority Sources.

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