'Basic Antenna' Project

Hello Graham,

You are more than welcome, any time.

I do apologise for not responding sooner, but I have been fully occupied in other areas, such as teaching. I am off home now (23:30 PM !!). Left the hotel at 21:30PM. Not much time for social media today :-(

Very best regards from Harry - SM0VPO

Thank you Harry. This is exactly what I am after.

Hello Graham,
Yes, your statements are 100% correct. The impedance does vary from 72Ω at the centre to a few thousand at the end. The impedance at any point in the dipole is given by the formula for radiation resistance:

R = 72Ω / sin(2xPi / λ)²

where
x = distance from the end of the dipole
λ = wavelength (a full wavelength, the dipole is 1/2 wavelength)
Pi = 3.1415927

So you can pick a point and calculate the impedance at that point. Transpose the formula and you can find the feed point for any specific impedance.

Hope this helps you.

BR Harry

Thinking about the 'Basic Antenna' Project which uses a 4:1 balun to feed a dipole off-centre, is there a formula / graph / nomogram which shows the impedance in a resonant dipole over its length? Not linear,  As in I know the centre is ~70 ohms, I've read that the end is ~3000 and this project implies ~200 - 300 at 1/3 length. Knowing this could ease HF antenna construction at my home.