Amateur Radio Calculators
Free amateur radio (HAM) calculators: antenna length, path loss, SWR ratio, repeater coverage, impedance matching, and more ham radio tools.
Antennas, feedline, propagation and power. 14 calculators for amateur radio (HAM) operators, from dipole cutting lengths to path loss budgets.
Dipole length uses the 468 divided by frequency in MHz formula for a half-wave in feet, and the important part is what that number is for. It is a starting point, not a final dimension. The velocity factor of real wire, height above ground, and nearby objects all shift resonance, so the practice is to cut long, measure, and trim. Cutting to the calculated length exactly and soldering the ends is how people end up with an antenna resonant 200 kHz off where they wanted it.
SWR is where the useful perspective sits. A 2:1 standing wave ratio sounds alarming and reflects about 11% of forward power, which is roughly half a dB. That is inaudible. Chasing 1.1:1 on an antenna that already reads 1.5:1 is effort spent for nothing measurable, while feedline loss on a long run of thin coax is frequently costing several dB and gets ignored.
Coax loss pages take cable type, length and frequency together, since loss per 100 feet rises steeply with frequency and a cable fine on 40 metres can be a poor choice on 70 centimetres.
Ham Radio Antenna Q and Bandwidth Calculator
Calculate antenna bandwidth from Q-factor and resonant frequency. Get -3dB bandwidth and 2:1 SWR bandwidth for HF, VHF, and UHF antenna designs.
Quarter-Wave Vertical Antenna Calculator
Calculate quarter-wave vertical antenna length and ground radial dimensions for any amateur radio frequency. Includes loading coil for shortened verticals.
Yagi Antenna Calculator
Calculate Yagi antenna element lengths and spacing for 3 to 6 element designs. Find driven element, reflector, and director dimensions for any band.
Antenna Gain Calculator (dBi)
Calculate antenna gain in dBi and dBd, effective radiated power, and compare dipole, Yagi, and directional antenna types for ham radio and RF link budgets.
Coax Cable Signal Loss Calculator
Calculate coaxial cable signal attenuation in dB from cable type, length, and frequency. Covers RG-8, RG-58, RG-213, and LMR-400 for HF, VHF, and UHF.
Dipole Antenna Length Calculator
Calculate dipole antenna lengths at any frequency using 468/f(MHz). Returns total and per-element dimensions in feet and meters for HF, VHF, and UHF bands.
Ham Radio Power Supply Sizing Calculator
Calculate the DC power supply current rating for an amateur radio station from transmitter power and accessory draw, with wire gauge and headroom advice.
Ham Radio Repeater Offset Calculator
Calculate repeater offset and TX/RX frequency for 2m, 70cm, and 23cm ham radio bands. Returns standard IARU offsets for North American and European plans.
Ham Radio Wire Antenna Length Calculator
Calculate wire length for dipole, inverted-V, and end-fed half-wave antennas from MHz. Returns each leg and total using the 468/f formula with velocity factor.
dBm to Watts Converter
Convert between dBm, watts and dBW for amateur radio power levels, with the nearest reference point named and what a 3, 6 or 10 dB change would do.
Free-Space Path Loss Calculator
Calculate free-space path loss (FSPL) between two radio stations in dB, then add power, antenna gains and feedline loss for a full link budget and margin.
Repeater Coverage Calculator
Estimate the radio horizon and coverage radius of a ham radio repeater based on antenna height. Uses line-of-sight radio propagation formula.
SWR and Reflected Power Calculator
Calculate Standing Wave Ratio (SWR) from impedance mismatch, and find the percentage of power reflected back. Used for antenna and feedline tuning.
Wavelength and Frequency Calculator
Convert MHz to metres and back, identify the amateur band and its edges, and get the electrical length inside coax or open-wire line at its velocity factor.