Tools · Antennas

Antenna Trimmer

Your wire is resonant — just not where you want it. Tell it where the SWR dips now and where you want it, and it tells you exactly how much to cut or add.

Where the SWR is lowest right now, from your analyzer or by sweeping the band.

Both legs combined for a dipole. If blank, it's estimated from the standard formula.

Enter your measured and target frequencies
to get a trim recommendation.

The math: wire length and resonant frequency are inversely proportional, so new length = current length × (fnow ÷ ftarget). Resonant below your target means the wire is too long — cut. Resonant above means too short — add.

  • Sneak up on it. Cut about 75% of the recommendation, re-measure, and repeat. Wire is much easier to cut than to splice back on.
  • Trim both legs equally on a dipole or inverted-V, or the pattern and feedpoint match suffer.
  • To lengthen a wire, splice on extra and fold back excess — folding back effectively shortens without cutting, handy for fine-tuning.
  • Height and surroundings matter. Resonance shifts as the antenna is raised, lowered, or moved near structures — always measure in the final position.
  • The estimate formulas (468/f half-wave, 234/f quarter-wave, 585/f ⅝-wave, 1005/f full-wave loop) are starting points; your measured length is always more accurate.
  • Loops: the length is the full circumference — trim or splice on the side opposite the feedpoint to keep it symmetric.
  • ⅝-wave verticals aren't resonant at the feedpoint by themselves — they need a matching coil at the base. Trim for the SWR dip with the matching network in place.