# How to compute the required length and turns for an air-cored antenna

I'm experimenting with RF reception in the 433MHz band and have made the most simple "whip" monopole antenna with 17.6 centimeters of wire.

Out of curiosity, I tried various designs for the antenna among which the one described in the step by step instructions created by Ben Schueler in 2013 and republished a large number of times since then, such as here

This design also works quite well for my application and using online calculators such as this one and this one, I can compute the inductor value.
But why is 0.220µH right?
And what about the size of the two straight parts? They are given as 17 and 53 millimeters but how does one gets these values?

I'm asking because I would like to replicate this design, but tuned for 868MHz reception.

Would you have the link to a reference document so that I can compute the values for 868MHz myself? Or should I just go ahead and divide every value by two as 868 is roughly 433 multiplied by two?

Thanks for any pointers.

• Hello and welcome to ham.stackexchange.com! Mar 24, 2021 at 15:26
• What is your actual goal? Why not just use a simple 8 cm monopole? Your linked site implies the loaded antenna works better, which may be true in his case but is not true in general. Mar 24, 2021 at 17:07
• Well, one of the goal would be to use smaller antennas that less prone to being bent, especially with the 433MHz one. But it's also a matter of curiosity. Mar 24, 2021 at 17:11