Amateur Radio Formulas
Amateur radio formulas size antennas, predict resonance, and evaluate standing-wave ratio for your band of choice. These calculators help operators cut dipoles and tune feedlines accurately. They are a staple of every ham’s bench.
Amateur Radio Formula Calculators
- Quarter-Wave Antenna Length l = c × VF / (4 × f) Frequency 100 kHz, Velocity Factor 2.5 % → Antenna Length = 18.74 m
- Half-Wave Dipole Length l = 0.95 × c / (2 × f) Frequency 100 kHz → Dipole Length = 1.424 km
- Coaxial Stub Length (λ/4) l = c / (4 × f) Frequency 100 kHz → Stub Length = 0.7495 km
- Effective Isotropic Radiated Power EIRP = Ptx + Gant − L_cable (dB) TX Power -4.4 dB, Antenna Gain 0.2 dB, Cable Loss 0.3 dB → EIRP = -4.5 dB
- SWR Reflected Power P_refl = P_fwd × ((SWR−1)/(SWR+1))² Forward Power 22 mW, SWR 0.025 → Reflected Power = 19.91 mW
- Antenna Beamwidth θ ≈ 70 × λ / D Wavelength 1 mm, Aperture Diameter 2.2 mm → Beamwidth = 31.82 °
Worked result for every Amateur Radio formula
| Formula | Expression | Worked result |
|---|---|---|
| Quarter-Wave Antenna Length | l = c × VF / (4 × f) | Frequency 100 kHz, Velocity Factor 2.5 % → Antenna Length = 18.74 m |
| Half-Wave Dipole Length | l = 0.95 × c / (2 × f) | Frequency 100 kHz → Dipole Length = 1.424 km |
| Coaxial Stub Length (λ/4) | l = c / (4 × f) | Frequency 100 kHz → Stub Length = 0.7495 km |
| Effective Isotropic Radiated Power | EIRP = Ptx + Gant − L_cable (dB) | TX Power -4.4 dB, Antenna Gain 0.2 dB, Cable Loss 0.3 dB → EIRP = -4.5 dB |
| SWR Reflected Power | P_refl = P_fwd × ((SWR−1)/(SWR+1))² | Forward Power 22 mW, SWR 0.025 → Reflected Power = 19.91 mW |
| Antenna Beamwidth | θ ≈ 70 × λ / D | Wavelength 1 mm, Aperture Diameter 2.2 mm → Beamwidth = 31.82 ° |
Variables used across Amateur Radio formulas
- l — Physical antenna length (m)
- f — Operating frequency (Hz)
- VF — Velocity factor (0-1, typically 0.95 for wire)
- EIRP — Effective isotropic radiated power (dBm)
- P_tx — Transmitter output power (dBm)
- G_ant — Antenna gain relative to isotropic (dBi)
- L_cable — Total feed line loss (dB)
- P_reflected — Power reflected back toward the transmitter (W)
- P_forward — Power traveling toward the antenna (W)
- SWR — Standing wave ratio (dimensionless, ≥ 1)
- θ — Half-power beamwidth (degrees)
- λ — Wavelength (m)
- D — Antenna aperture diameter (m)
Related Formula Categories
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