Antenna Calculator
Element lengths for the antennas SDR and radio hobbyists build most, with diagrams.
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Listen and decode with NyxScope
Built your antenna? Plug it into an RTL-SDR and watch aircraft appear on the map, plus ships, weather sensors and trunked radio. NyxScope is a free multi-protocol SDR scanner for Windows from ICBizLabs, the team behind kilaz.com, with a 30-day trial of its licensed features.
About this tool
Why lengths are shorter than the wavelength
A real wire behaves slightly longer than its physical length (end effect), so a half-wave dipole is about 95% of a true half wavelength. Cut a little long and trim while watching SWR.
Coaxial collinear
A collinear made from coax uses the cable's velocity factor, so element length depends on the exact cable. Foam RG-6 is around 0.82–0.85, solid-PE RG-58 around 0.66: check the datasheet.
Which antenna for what
ADS-B: a 1090 MHz collinear or ground plane, mounted high. METEOR weather satellites: a V-dipole or QFH. General scanning: a discone. Ham 2 m/70 cm: a ground plane or J-pole.