'Basic Antenna' Project

Post new topic   Reply to topic

View previous topic View next topic Go down

Re: 'Basic Antenna' Project

Post by Admin on Wed Oct 18, 2017 9:42 pm

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

_________________
(Thanks to those who tried and couldn't make the QSO. Back on 14.200MHz Sundays from the 24th Sept.)
avatar
Admin
Admin

Posts : 441
Join date : 2012-11-24
Age : 66
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

Re: 'Basic Antenna' Project

Post by GrahamH on Sun Oct 15, 2017 11:21 pm

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

GrahamH

Posts : 2
Join date : 2017-09-19
Location : Australia

View user profile

Back to top Go down

Re: 'Basic Antenna' Project

Post by Admin on Sun Oct 15, 2017 5:59 pm

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

_________________
(Thanks to those who tried and couldn't make the QSO. Back on 14.200MHz Sundays from the 24th Sept.)
avatar
Admin
Admin

Posts : 441
Join date : 2012-11-24
Age : 66
Location : Märsta, Sweden

View user profile http://www.sm0vpo.com

Back to top Go down

'Basic Antenna' Project

Post by GrahamH on Sun Oct 15, 2017 3:25 am

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.

GrahamH

Posts : 2
Join date : 2017-09-19
Location : Australia

View user profile

Back to top Go down

Re: 'Basic Antenna' Project

Post by Sponsored content


Sponsored content


Back to top Go down

View previous topic View next topic Back to top

- Similar topics

Post new topic   Reply to topic
 
Permissions in this forum:
You can reply to topics in this forum