Coax Loss Calculator
How much of your transmitted power actually reaches your antenna? Compare RG-213/U, RG-8X and LMR-400 reference cables alongside the Messi & Paoloni coaxial cables available from ML&S, including their RG-58. Enter your frequency and cable length to see the difference.
Calculate your feed-line loss
Results update automatically. Minimum frequency: 1.8 MHz. Frequencies are in MHz and lengths are in metres. Cables are displayed from highest calculated loss to lowest.
RG-213/U (Reference) uses the alternative comparison figures at 1.8–144 MHz, with Messi & Paoloni comparison figures above 144 MHz. Actual RG-213 attenuation varies by manufacturer.
Your coax loss comparison
For a matched 50 ohm system, the power delivered figure is the percentage of input RF power remaining at the far end of the cable, before connector and mismatch losses.
| Cable | Loss per 100 m | Loss over your length | Power delivered |
|---|---|---|---|
| Calculating results… | |||
Why does coaxial cable loss matter?
Every coaxial feed line absorbs some RF energy. As the frequency increases or the cable becomes longer, more signal is lost before it reaches the antenna. The same attenuation affects weak received signals travelling back to the receiver.
Length matters
At a given frequency, cable attenuation in decibels is approximately proportional to its length. A 20 m run has about one fifth of the published 100 m loss.
Frequency matters
A coax that works well on HF can introduce substantial attenuation at 144 to 146 MHz or 430 to 440 MHz, particularly over longer runs.
Construction matters
Modern low-loss cables use carefully engineered conductors, dielectrics and screening to reduce attenuation. Flexibility and installation suitability are also worth comparing.
Understanding the figures
Loss per 100 m: the cable's specified attenuation in decibels at your selected frequency, standardised to 100 metres. Loss over your length: attenuation scaled to the length entered. Power delivered: the percentage remaining at the output, calculated as 100 × 10(−loss in dB / 10).
For example, 3 dB of cable loss means roughly half the input power reaches the other end. At 6 dB, only about one quarter remains. Lower attenuation is better, but the ideal cable also depends on its flexibility, dimensions, weather resistance and installation.
Need coax with plugs already fitted?
We sell the Messi & Paoloni coaxial cables shown in this calculator and can prepare custom cable assemblies to your required length, with compatible connectors fitted and the finished cable tested. Choose your cable, specify the length and select a connector for each end using our online cable builder.
Build Your Custom Coax Cable
