My Antenna is not a Windom
Posted by g7fek on Thu, 23 Jul 2009 17:25:25 +0100

Today I received another email telling me my G7FEK nested Marconi is really a Windom antenna. Please guys - no it isn't........

Hello Mike.
 
            Let me introduce my self my name is XXX and I have been a radio ham for fifty years, I love antenna building and playing with the big amps 1.5Kw plus it’s fun, the reason why I have got in touch with you is because a friend of mine who has the internet told me about a antenna from the UK the G7FEK antenna seeing a copy of the screen from the internet it looks like the one I was playing with about forty years ago, I was told from  my friend that it’s your design this can’t be this was a early version of the shorty forty Windom which I feed with 450 Ohms Twin now they feed it with Coax in to a 4:1, I’m sorry old man but please don’t put your name to something that’s not yours.
 
Best regards XXX 

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Hi XXX (Name removed to protect the innocent),

Many thanks for your email.

Just so that you are correctly informed, my antenna is derived from the original Marconi vertical antenna invented pre 1900. It isn't a Windom and does not follow Windom principals.

The Windom principal was discovered in 1929 by Loren Windom and is not an invention in itself, but a discovery and enhancement of the horizontal hertzian resonant dipole antenna. His idea was to feed a horizontal dipole using an unbalanced single feed wire (more recent variations use balanced twin or 4/6:1 balun and coax). It was always fed at the even harmonic impedance coincidence point, approximately 1/3rd of the length from the end of the horizontal dipole.

I don't make any claims to Marconi's antenna either, hence my adaption of Marconi's antenna is referred to, quite rightly, as a "Nested Marconi Antenna".

A 40m Windom would need to be around 65 feet long on the horizontal. and fed about 21.5 feet from one end. It would not work well, or achieve resonance on 80m, as my antenna does quite successfully. It would only be truly resonant and achieve match on 40/20 and 10 meters.

My antenna works like three antennas in one. It's primary action uses odd harmonic resonance of quarter waves in the vertical plane, of which only one half, or the other half of the antenna is active depending on the primary band in use, and on 10MHz the antenna also achieves some equivalent dipole radiation. There is no specific horizontal section, therefore it offers no resemblance to the Windom whatsoever. It does on 10MHz, offer a similar radiation pattern to the Windom, but only due to the presence of both vertical and horizontal components. This also happens on the Windom, but on All of its bands.

You will see that the wire feed used on my antenna is neither a single wire (as in the original Windom) nor a balanced feeder (as in the commonly adapted Windom design) and it is NOT fed with as a horizontal with a 4:1 balun either. So it also offers no resemblance to any known design of Windom, including the one to which you refer.

In my antenna, unlike a Windom, both sides of the vertical section are fed "in the same phase" but only one side is capable of coupling energy on any particular band, due to the differing impedance. The Windom feeds the entire horizontal dipole on ALL bands and relies on the coinciding impedance to match the even harmonics only, to achieve coupling on each band. A completely different operation and matching method from my Antenna. The Windom radiation is predominantly horizontal with an additional vertical component from the out of balance feeder, the opposite of my antenna.

Please feel free to study both antennas further, model it on EZNEC and compare it to the Windom. You will clearly see the differences.

Thanks for your comments, I'm always pleased when Amateurs' take a keen interest in Antenna design.

Best Regards,

Mike, G7FEK.

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Please guys, before you write to me telling me my antenna is a Windom or off centre fed dipole, please read the article - don't just look at the pictures!!!. My original article opener reads as follows....

"The clever people among you will notice that, although at first glance this looks like a small "off centre fed" dipole, this is actually a two element nested Marconi 1/4 wave for the lower HF bands, giving a low angle of radiation and predominantly vertical polarisation."

It's all already there in black and white!!

Click for the Original 80m Antenna for Small Gardens Article


All the best,

Mike.







Comment by 'Richard W.' on 24 Feb 2017 - comment
“Built your antenna and put it up today, very pleased with it working JT65! Europe was mine on 17 meters, QSO'd with Northern European stations not normally heard in NW Florida. 20 meter performance has also been excellent. Thank you so much for a excellent small lot antenna design!”

Comment by 'Fred W' on 28 Apr 2015 - comment
“I think people just look at the picture not the article. I like your PDF article. Very detailed. Many thanks for a great antenna. Its given me 80m for the first time, plus many other bands. I only have a small lot.”