#amateur-radio

Antenna length maths as an API, computed locally and deterministically. The dipole endpoint gives the total and per-leg length of a half-wave dipole for a frequency, in metres, feet, inches and centimetres, applying a velocity factor (about 0.95 for wire) and also reporting the classic 468 ÷ f(MHz) feet rule of thumb. The quarterwave endpoint gives the element length of a quarter-wave vertical or monopole, with the 234 ÷ f(MHz) rule. The element endpoint computes the length of an element at any fraction of a wavelength — full-wave, half-wave, quarter-wave, fifth-wave, five-eighths or a custom fraction. Frequencies accept Hz, kHz, MHz and GHz, and the velocity factor is configurable. Everything is computed locally and deterministically, so it is instant and private. These are starting lengths: real antennas need trimming and tuning for the lowest SWR, as end effects and surroundings shift the resonant length. Ideal for amateur-radio and RF tools, antenna and IoT design, and electronics education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is antenna geometry; for general wavelength, frequency and photon energy use a wavelength API.

api.oanor.com/antenna-api

Convert between latitude/longitude and the Maidenhead Locator System — the grid-square "QTH locator" (like JN58td or IO91wm) used by amateur radio, APRS and contesting to describe a position compactly. The encode endpoint turns a latitude and longitude into a locator at 4-, 6-, 8- or 10-character precision. The decode endpoint turns a locator back into the centre coordinates, the south-west corner and the size of the grid square. The distance endpoint gives the great-circle distance (kilometres and miles) and bearing between the centres of two locators — the classic "how far and which way is that station". Everything is computed locally and deterministically, so it is instant and private. Ideal for amateur-radio and APRS tools, contest logging, antenna aiming, and grid-based mapping. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is the Maidenhead system; for Plus Codes, MGRS, UTM and DMS use a geo-convert API and for precise geodesic distance use a geodesy API.

api.oanor.com/maidenhead-api