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Antenna calculator
2 m and 70 cm
Pick the band, antenna, power and height — and I’ll calculate the dimensions to build the antenna , the radiated power (EIRP) and the estimated range of the contact: radio horizon and link budget. Perfect for checking ‘will I get through’ before a trip.
Your station
// set the parameters — the result updates automatically
Antenna dimensions
Approximate dimensions (for wave velocity in wire ~0.95). Trim the final length for minimum SWR — conductor thickness, insulation and surroundings shift the resonance.
How I calculate it
Nothing magical — three physical limits, and the actual range is the lowest one (corrected for terrain).
Radio horizon — on VHF/UHF the wave travels “straight ahead”, so the height of both antennas is key. Formula with a correction for atmospheric refraction: d[km] ≈ 4.12 × (√h₁ + √h₂), where h is in metres. That’s why an antenna on the roof beats 100 W from the basement.
Link budget — whether the signal is strong enough to be heard. I add up power, antenna gains and cable loss (EIRP), subtract free‑space path loss FSPL = 32.44 + 20·log(d) + 20·log(f) and compare with the receiver sensitivity threshold. If there’s headroom — the contact reaches a little beyond the horizon (diffraction), so more power really does extend the range, though with diminishing returns.
Terrain — the formulas assume clear line of sight. Buildings, forest and hills cut the range, so I multiply the result by a terrain factor. This is an estimate, not a guarantee — a real QSO can be both longer (reflections, tropo) and shorter (an obstacle in the first Fresnel zone).
Frequencies and repeaters
Ready-made FM simplex channels and active Warsaw repeaters — to load into your radio in 5 minutes.