Coaxial Cable Loss Calculator

Coaxial cable loss: attenuation in dB per length

Coaxial cable attenuation is usually tabulated in dB per 100 m (or per 100 ft) at a reference frequency, and grows with frequency due to the skin effect and dielectric loss. For a length L at frequency f the total loss is LdB = α(f) · L. Reference numbers: RG-58 ≈ 5 dB/100 m at 100 MHz; RG-213 ≈ 1.5 dB/100 m; RG-6 ≈ 1.8 dB/100 m at 100 MHz (≈10 dB/100 m at 1 GHz); LMR-400 ≈ 1.0 dB/100 m. Example: 20 m of RG-58 at 100 MHz → 20 × 0.05 = 1 dB of loss, equivalent to ≈21% power drop. Compared with optical fibre (≈0.2 dB/km at 1550 nm), coax loses thousands of times more — that is why long-distance backbones are fibre, not copper.

Applications: antenna feeds, cable TV, DOCSIS broadband, broadcasting

Cable-loss calculations guide antenna sizing (keep the run between antenna and radio as short as possible), cable-TV plant design (in-line amplifiers compensate for loss), DOCSIS broadband, broadcast telecom and laboratory RF where the link budget must close.

FAQ

Why does loss grow with frequency? The skin effect forces current to the conductor surface, raising effective resistance; dielectric losses also rise with frequency.

How much loss is acceptable? Rule of thumb: keep total loss under 3 dB (≈50% power) — above that, choose a thicker cable or shorten the run.

Does an amplifier solve the problem? It compensates the loss but also amplifies noise; better to reduce the loss first (shorter run, better cable).

Fibre versus coax? Fibre loses ≈0.2 dB/km vs ≈50 dB/km on coax at the same frequency — fibre dominates for long distances.