Rubber-Ducky Helical Antenna ~868MHz/~915MHz Template

thingiverse

Printed template for DIY small 868MHz (red)/ 915MHz (green) antenna, 26x6mm alternative to 160mm dipole. Use 0.7mm wire for the spring part - look for details to the link below. Use coaxial IPEX4 antenna cable and plug proper for you receiver, solder active, central wire to the spring (no passive part necessary, it should to be insulated). Don't expect that it will be perfectly tuned, but I have got hundreds meters of range with 30% RSSI and maximum available ExpressLRS LQ using 50mW transmitter (FrSky r9m). Use shrink tube to secure the wires. It can be helpful to create the spring only part and use it without printed part but keeping the template inside of the spring will keep the shape unchanged. 868MHz tested and working fine for FrSky r9mm flashed to ExpressLRS, 915MHz not tested as I haven't TX (I'm in EU). Use wisely at your own risk, make sure it works as expected. All credits goes to https://e.pavlin.si/2018/06/29/small-normal-mode-antenna-for-868mhz/ . Comments - I did my best finding 915MHz version specification (9 turns for 12.5mm sprint and 4.5mm leg) - it is important to leave unsoldered bottom 6mm straight part - use lighter to gently remove insulation from antenna cable, clean the wire - solder wire to the hook, not to the 6mm straight antenna part - secure active antenna cable to make sure it will stay soldered (it is most important part)