Cut an antenna to length for your frequency
145 MHz needs a 49 cm quarter-wave whip. The same formulas scale from HF wire dipoles to a 2 m full-wave loop.
Tools used in this guide
The job
Antennas are tuned by length: a dipole is a half-wave split into two legs, a vertical whip is a quarter-wave, and a full-wave loop closes on itself. All start from wavelength = c/f, scaled by a velocity factor (~0.95) for a bare wire.
One frequency, four lengths
Enter the frequency in MHz; the tool reports the wavelength, the dipole total and per-leg length, quarter-wave, 5/8-wave, and full-wave loop.
Worked example
145 MHz (2 m amateur band): wavelength 2.068 m, dipole total 0.982 m (0.491 m per leg), quarter-wave 0.491 m, 5/8-wave 1.228 m, full-wave loop 2.109 m.
Scope
0.1–30,000 MHz. The 0.95 velocity factor suits plain wire; insulated wire, proximity to ground, and feedline detune a real antenna — cut long, then trim against an SWR meter.