Free Coaxial Cable Loss Calculator
Calculate RF signal attenuation in decibels (dB), transmitted power lost as heat, and delivered watts at the antenna from HF ham radio to 5.8GHz microwave.
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📊 Attenuation & Power Delivery
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Understanding RF Coaxial Cable Attenuation
At radio frequencies, coaxial cable loss increases exponentially with frequency due to two physical phenomena: the skin effect (high-frequency currents flow only in the outermost micron of the center conductor) and dielectric heating losses within the polyethylene or foam insulator.
The 3 dB Loss Rule
In decibels, a 3.0 dB loss cuts your transmitted RF power exactly in half (50% lost). A 6 dB loss reduces power to only 25%, while a 10 dB loss destroys 90% of your signal before it reaches the antenna.
Why RG-58 Fails at UHF & Gigahertz
While cheap RG-58 cable is adequate on HF frequencies (14 MHz), its attenuation at 440 MHz UHF is a devastating 11 dB per 100 feet (destroying 92% of your power!). Switching to LMR-400 reduces this loss to just 2.7 dB.
Frequently Asked Questions
What is the difference between 50-ohm and 75-ohm coax?
50-ohm cable (RG-58, LMR-400) is the global standard for RF two-way transceivers, ham radio, and WiFi because it balances power handling and minimum dielectric loss. 75-ohm cable (RG-6) is optimized for lowest signal attenuation in receive-only CATV and satellite installations.
Does high SWR increase cable loss?
Yes. When high standing waves reflect back down the transmission line from a mismatched antenna, that reflected energy bounces back and forth repeatedly, suffering additional attenuation on every pass and heating the coaxial jacket.
How does line length scale attenuation?
Line loss in decibels scales linearly with length. 100 feet of cable has exactly double the decibel loss of 50 feet of the same cable.