Just a quick question, according to this link to make simple helical antenna for 868 Mhz
Turns = 9, Coil Diam = 5.5mm, Wire Diam = 0.8mm, Coil length = 13mm
The groundplane stub between last turn and solder stub = 4.5 mm
Is there any calculator to find the number of turns for 867 MHz? Or it does not matter that much.