'Basic Antenna' Project
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Re: '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
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
_________________
If success = A, then A = X + Y + Z, where X = work, Y = play and Z = keeping your mouth shut (Albert Einstein).
Admin Admin
 Posts : 722
Join date : 20121124
Age : 67
Location : Märsta, Sweden
Re: 'Basic Antenna' Project
Thank you Harry. This is exactly what I am after.
GrahamH Posts : 2
Join date : 20170919
Location : Australia
Re: 'Basic Antenna' Project
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
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
_________________
If success = A, then A = X + Y + Z, where X = work, Y = play and Z = keeping your mouth shut (Albert Einstein).
Admin Admin
 Posts : 722
Join date : 20121124
Age : 67
Location : Märsta, Sweden
'Basic Antenna' Project
Thinking about the 'Basic Antenna' Project which uses a 4:1 balun to feed a dipole offcentre, 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.
GrahamH Posts : 2
Join date : 20170919
Location : Australia
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