Re: Some practical values for a half-wave dipole antenna

by **admin** Sat May 25, 2013 10:42 am

You are most welcome any time but if you have any specific idea as to the antenna you want then please come back. Ivan i8s especially good at antennas and I have some experience, not to mention all the other people here who are keen to help you.

BR Harry - SM0VPO
Nerja, Spain

by Dyon Tue May 21, 2013 1:23 am

Thank you all for the information.
Regards.

by **admin** Fri May 17, 2013 5:37 pm

http://www.sm0vpo.com/antennas/anten.htm - how antennas work
http://www.sm0vpo.com/antennas/dipole.htm - basic antenna
http://www.sm0vpo.com/antennas/vpole0.htm - quick with calculator

BR Harry

by DragonForce Thu May 16, 2013 2:09 pm

Dyon wrote:Hi Ivan,
I do not have any particular frequency in mind.
All I want is a complete info about a working half-dipole antenna (center-fed). The frequency does not matter much for my present purpose but it must be that antenna's fundamental and higher harmonics. I am interested to make some calculations.
The radiation pattern should be -if at all possible- the pattern for free space (away from ground) for the fundamental and some higher harmonics. The pattern must be measured, not calculated.
I will appreciate any help.
Thanks, Ionel

But the length of a half wave dipole will depend upon the frequency you wish it to be resonant at - it's like asking "How long is a piece of string".

The approximate length of a halfwave dipole (in feet) can be found from 468/MHz. That gives you the total length - obviously divide by two and feed the antenna at the centre point (quarter lambda up, quarter lambda down, assuming a vertical antenna). Impedance at the quarter wave feed point is 75R I believe.

See here for precise information: https://en.wikipedia.org/wiki/Dipole_antenna

by Dyon Thu May 16, 2013 1:26 pm

Hi Ivan,
I do not have any particular frequency in mind.
All I want is a complete info about a working half-dipole antenna (center-fed). The frequency does not matter much for my present purpose but it must be that antenna's fundamental and higher harmonics. I am interested to make some calculations.
The radiation pattern should be -if at all possible- the pattern for free space (away from ground) for the fundamental and some higher harmonics. The pattern must be measured, not calculated.
I will appreciate any help.
Thanks, Ionel

by **Ivan** Wed May 15, 2013 4:08 pm

Hi,
what band are you interested in ?
The voltage and current depend on the power in use (really much !! Laughing

). They are also affected by the surroundings - height above ground, nearby metallic objects etc.
Measuring of the radiation pattern is out of possibilities of an average ham on longer than decimeter waves. Probably a copter would be required ...

BR from Ivan

by Dyon Wed May 15, 2013 9:46 am

Hi,
I would like to know the parameters of a real-life, working, tested, half-wavelength dipole antenna (center-fed).
I would appreciate if you could help me with information on:
- physical dimensions, length/diameter
- material used
- fundamental frequency (not theoretical, practical)
- amplitude of the voltage at the feeding point
- amplitude of the current
- measured radiation pattern
Many thanks, Ionel

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