Read the loss in context
Use the result to compare cable choices and estimate received or delivered power before installation. Enter loss data for the exact cable and frequency when available.
Coax Loss – Approximate Estimate
Rough educational estimate only. Uses simplified √f scaling and a simplified SWR-loss factor — not a full transmission-line model. Prefer manufacturer data for design decisions.
Inputs
Matched loss—
Mismatch loss (load reflection)—
Total loss—
Approx. velocity factor—
Electrical length—
Power delivered (100 W in)—
This is a simplified estimate using typical reference attenuation values, √f frequency scaling, and load mismatch loss. Real cable loss depends on construction, temperature and frequency in a more complex way. Always prefer manufacturer attenuation tables for accurate design.
Coax Loss
Matched loss is the normal attenuation. High SWR increases current and therefore additional heating loss. Keep feedlines short on the higher bands and use low-loss cable for long runs.
Why the installed cable can differ
Manufacturer loss figures vary with frequency, temperature, connectors, bend radius and cable condition. A generic loss value can be misleading on long runs or at higher frequencies.
What to verify on the feedline
Use the cable manufacturer data sheet for final design, and include connector and jumper losses when the link budget is tight.
Reading coax loss in a real station
Coax loss is usually specified as a value at a particular frequency and cable length, so the most useful comparison keeps both variables visible. Loss in dB is logarithmic: a small numerical change can represent a meaningful change in delivered power. Long feedlines and higher frequencies generally make cable selection more important, but a low-loss cable is not automatically the best choice if it is difficult to route, terminate or weatherproof. Use the calculator with the manufacturer's loss data whenever possible rather than relying on a generic cable value. Connectors, adapters and imperfect installation can add loss that the basic calculation does not include. For a finished station, compare the expected feedline loss with measured transmitter-side and antenna-side values when suitable equipment is available. This helps distinguish a cable problem from an antenna mismatch or another fault in the RF path.
If the calculated loss seems unexpectedly high, check the cable length and frequency first, then verify the manufacturer's attenuation units. Mixing dB per metre with dB per 100 metres is a common source of otherwise plausible but incorrect results.