Calculators & Tools
Coaxial Cable Length & Loss Calculator
Every coaxial cable introduces signal loss. As operating frequency increases, feedline attenuation increases. Longer cable runs also result in greater loss. This calculator estimates total coaxial cable loss using commonly used amateur radio feedlines and helps determine how much transmitter power actually reaches the antenna.
Enter cable type, frequency, and length
MHz
ft
W
Loss Status Levels
Excellent< 1 dBMinimal loss. Excellent feedline efficiency.
Good1 – 2 dBSuitable for nearly all amateur radio installations.
Fair2 – 3 dBAcceptable, but lower-loss feedline may improve performance.
Poor3 – 6 dBConsider upgrading to a lower-loss cable.
High Loss> 6 dBA significant portion of transmitter power is lost in the feedline.
Reducing Feedline Loss
- Keep feedline runs as short as practical.
- Use low-loss coax for VHF and UHF installations.
- Weatherproof outdoor connectors.
- Avoid unnecessary adapters.
- Inspect coax periodically for water intrusion and physical damage.
- Replace aging or damaged feedline.
Typical Recommendations
HFMost coax types perform adequately over moderate distances.
VHFLMR-240 or better is recommended for longer runs.
UHFLMR-400 or lower-loss cable is strongly recommended.
MicrowaveUse the lowest-loss feedline available.
Formula Reference
Total LossLoss (dB) = (Length ÷ 100) × dB/100ftCoax attenuation is expressed in dB per 100 feet. Scale by the actual run length.
Power at AntennaPout = Pin × 10−Loss/10Convert dB loss to a power ratio to find actual watts delivered to the antenna.
Attenuation values in this calculator are representative estimates for amateur radio planning purposes. Actual values vary by manufacturer, connector quality, temperature, and cable condition. Always consult manufacturer datasheets for precision RF engineering work.