Use the free tool above, then read on for how it works, a worked example, and practical tips.
What this tool does
Every metre of coax cable eats a little of your signal before it reaches the antenna, and the loss grows with length and with frequency. This calculator tells you how many decibels you lose on the cable run and how much signal is left at the far end, so you can judge whether a longer run or a better cable is worth the cost.
How it works
The tool starts from each cable type’s loss at 100 MHz and scales it with the square root of your frequency, because coax loss rises roughly with the square root of frequency rather than in a straight line. It then multiplies by your cable length and adds a small allowance of 0.1 dB per connector, which is a fair planning figure for decent connectors in good condition.
How to use it
- Enter your values in the boxes above.
- Press the calculate or play button.
- Read the result shown below the tool.
- Try a second set of values to compare options.
Worked example
Take 30 metres of RG-58 at 145 MHz. The base loss of 0.60 dB per 10 metres scales up at the higher frequency, and with two connectors the total comes to roughly 2.4 dB, leaving about 58 percent of your power at the antenna. Swap that run for LMR-400 and the same length loses well under 1 dB, which is why better cable pays off most on long runs and at VHF and UHF.
Practical tips
Keep cable runs as short as you can, and spend the money on the lowest-loss cable for the longest run in your station rather than upgrading every short patch lead. Check connectors first when a station suddenly sounds weak, because a corroded or loose connector can cost more than several metres of good cable.
Common mistakes
A common mistake is comparing cables only at one frequency, often the lowest one on the datasheet, and then being surprised at UHF where the same cable loses far more. Another is forgetting connectors entirely, or assuming a bargain cable with thin shielding performs like the branded cable it copies.
Questions and answers
Is this tool free? Yes. It runs in your browser, needs no account, and gives instant results.
Do I need to install anything? No. The tool works on any modern phone or computer browser.
How accurate are the results? The maths follows the standard formulas shown above. Real-world results vary with terrain, equipment, and conditions, so use the figures for planning.
Can I use it on my phone? Yes. The tool is designed to work on a phone screen, so you can use it at the operating desk, in the field, or at a club station without a computer.
Who uses this tool
Radio amateurs, students, and club members all use tools like this one, because they turn a formula from a book into an answer for your own station in seconds. Beginners use it to check homework and first setups, while experienced operators use it to sanity-check a plan before spending money on cable, masts, or antennas. Even a quick check can prevent a costly mistake, such as ordering the wrong cable length or aiming a beam in the wrong direction.
What to try next
- Run the tool with your real station values, not just the default numbers, so the answer means something for your setup.
- Change one input at a time and watch how the result moves, because that shows you which input matters most.
- Write the result in your station notebook next to the date, so you can compare later changes against a known baseline.
Safety note: this is an educational estimator only. Real transmissions need an amateur licence and must follow your local regulations, band plans, and power limits. Never transmit without the proper licence, and treat every result here as a planning guide, not professional or legal advice.
Versión en español: Calculadora de Pérdida de Cable Coaxial – Pérdida en dB para RG-58, RG-213 y LMR-400 Gratis