Random Wire / End-Fed Long Wire Calculator
Find practical random wire antenna lengths for multiband HF use. Get safe wire length suggestions, counterpoise guidance, and end-fed long wire estimates for portable or backyard operation.
Random Wire Antenna Planner
Operating target
Start with the lowest band you want to support. The calculator uses that as the floor.
Workflow
Choose whether you want a recommended starting length or you want to evaluate wire you already own.
Suggested safe lengths
Filter the common non-resonant lengths by the space you have available.
This mode filters a curated list of common non-resonant wire lengths and returns practical starting points for multiband use with a tuner.
Check the wire you already have
Enter the wire on hand and the calculator will estimate how practical it is as a starting point.
This mode treats the entered wire as your total wire on hand, then subtracts any dedicated counterpoise length to estimate the radiator length you can actually deploy.
Random Wire Starting Point Formulas
These are the sizing relationships used by this calculator.
Quarter-Wave Reference
Quarter-wave length (ft) = 246 / f(MHz)Wavelength Check
Wire length in wavelengths = Wire length (ft) / Wavelength (ft)Counterpoise Starting Point
Quarter-wave counterpoise = 1/4 wavelength on the lowest bandHow it works
Start by choosing the lowest band you want to cover. If you want a practical starting point, use Suggest a good length and the calculator will filter a curated list of tuner-friendly random-wire lengths. If you already own a spool or pre-cut wire, use I already have wire and the calculator will tell you how that length relates to the lowest band.
The goal is not to force a theory-first workflow. It is to help you answer the operating question most people actually have: What length should I throw in the air for the bands I want to use?
Practical deployment notes
- Start with the suggested length, then test the actual deployment with your tuner.
- Counterpoise choice matters. A short portable counterpoise can work, but a quarter-wave return often behaves more predictably.
- Height, slope, nearby trees, support lines, and feedline routing can all change the match.
- Longer wires can improve the lowest band, but they can also produce more unpredictable feedpoint impedance.
- Portable setups are often a compromise.
Common lengths and lengths to avoid
These are operator starting points, not absolute rules. The calculator checks your radiator length after counterpoise against the cautious list below so you can see when your remaining antenna wire lands near a commonly avoided starting point.
Common starting lengths
| Length | Metric |
|---|---|
| 29.0 ft | 8.8 m |
| 35.5 ft | 10.8 m |
| 41.0 ft | 12.5 m |
| 58.0 ft | 17.7 m |
| 71.0 ft | 21.6 m |
| 84.0 ft | 25.6 m |
| 107.0 ft | 32.6 m |
| 124.0 ft | 37.8 m |
| 148.0 ft | 45.1 m |
| 203.0 ft | 61.9 m |
Common lengths to test cautiously
| Length | Why operators check it carefully |
|---|---|
| 34.0 ft | Near a quarter-wave on 40m, which can create difficult feedpoint behavior. |
| 67.0 ft | Near a half-wave on 40m and a quarter-wave on 80m. |
| 100.0 ft | Near a three-quarter-wave relationship on 40m and often worth testing cautiously. |
| 134.0 ft | Near a half-wave on 80m, where end-fed impedance can become difficult. |
FAQ
Why avoid certain random wire lengths?
Some lengths repeatedly land near difficult feedpoint impedances on popular HF bands. Operators often start with common non-resonant lengths because they are easier to match across multiple bands with a tuner.
Do I need a counterpoise for an end-fed long wire?
Usually yes, or at least some intentional return path. A quarter-wave counterpoise is a strong starting point, while shorter portable counterpoises can still work with tuner experimentation.
Is this a starting point or exact design length?
It is a starting point. Real-world performance depends on tuner range, transformer choice, wire height, counterpoise, nearby objects, and how the wire is deployed.