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Portable 7-Band EFHW Antenna

After a long amateur radio break, I rediscovered this great hobby and especially SOTA about two years ago.

I tried and evaluated different HF portable antenna designs that fulfilled my personal needs, which finally brought me to experiments with resonant end-fed halve-wave antennas.

During these experiments, I came up with a EFHW design that I had not seen before: a radiator containing one bypassable loading coil for more bands to cover. The result is a 20m long EFHW antenna that is resonant on the 60-, 40-, 30-, 20-, 17-, 15- and 10m-band, depending if the coil is short-cut or in use.

Further, I experimented with small but efficient couplers, adding more bands to the antenna, and much more. All the measurements were taken during my SOTA activations.

Please have a look at the resulting A Portable 7-Band End-Fed Half-Wave (EFHW) Antenna document, consisting of more than 50 pages that I promised to several hams for so long.
Update: Linked to version 1.2 that contains more information about the transformer winding and several small fixes.

I hope that some contained ideas will be a useful source of inspiration for your own antenna projects.

73 Stephan

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Lots to read and think about in that document Stephan. :+1:

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Thank you for taking the time to write the document Stephen, a very interesting read.
73
Tim
G4YTD

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Thank you Stephan!
73 Fabio

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Thanks Stefan,
Very detailed info and some deep research! Thanks a lot for sharing with us.
I’ll have a read in holidays.

VY 73 de Ignacio

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Thanks Stephan for you EFHW antenna details. Very interesting and helpful. A great job in your research and report presentation. Well done. :grinning:

73 de Geoff vk3sq

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Thank you Stephan, an excellent well written document that contains some really interesting stuff.
I’ll be making one for sure when I get the time and the correct ferrite core.

73 Tony G1HMO

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Hi Stephan,
I’ve just read (briefly) through the article, and think it’s really good!
I’ve never come across using a loading coil in that fashion before.
Very well researched and I’m impressed with your construction from the mechanical perspective too. Most professional looking results. :grinning:

73, Steven

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Hi Stephan,

Antenna articles are always interesting and yours is no exception. Thank you.

i have built and tested and used quite a few EFD. Actually the best are Near End Fed Antennas with the coupling transformer placed near the end at about 10% of the length. This avoids the crazy business (IMO) of using the coax outer as part of the radiator and makes the antenna performance more predictable.

A lower ratio transformer should be used with this feed arrangement… Depending on the height above ground a 4:1 or 5:1 or 6:1 ratio will give the best compromise. I also use a separate primary winding to minimize common mode current on the feed line.

The minimum VSWR does not occur at resonance and as you say is a function of height above ground, transformer ratio and wire length.

I prefer a doublet with OWL as I think this is slightly more efficient but not every summit can accept this arrangement.

Happy activating.

73
Ron
VK3AFW

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Thank you all for your kind words!
I’m happy if I can give some new ideas for your own experiments, which to me is great fun to be carried out in nature. OK, maybe not at the Matterhorn.

Also, thanks a lot to the ones that sent me English spelling corrections!
For example, I didn’t know the difference between windings and turns in English. One can always learn new things, not only in the field of technology.

I’m happy to get further correction proposals, but bear in mind that I prefer to go for an activation, instead of staying inside, especially when there is good SOTA weather :wink:

I will then create a new document version and edit the link accordingly.

The new version will also include a link to a very interesting article that I saw by chance today:

It’s a very rare find of high quality, and backs several of my observations, which I found out empirically in the field.

73 Stephan

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Hi Stephan,

Let me first to congratulate you on excellent report, it’s very informative, practical and easy to follow even for novice like me. Many thanks.

I have one observation/correction to make. On page 25 you mention that 1/4wl on 40m band will be close to the top of the mast where wire bends for inv-L setup. Shouldn’t this be 20m band? I believe your mast is 6mtr high.

If so, could this be related to your unexpected minimal differences on various measurements for 20m band?

73 Marek

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A really recommendable article, thanks for the hint.
Let’s hope that it is also understood by the numerous downscaling experts and propagators of Ham myths :wink:

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Hi Marek,

Thanks for your feedback!

Sorry if I missed something or the following is obvious to you:

Most of the radiation happens in the middle of a dipole, be it center-fed or (nearly) end-fed. When using a 20m-long end-fed radiator for the 40-meter band, most of the radiation happens after 10m wire length. But before and after this point, still a lot of radiation happens, which diminishes towards both ends.

Therefore, with this configuration, the main radiation area is pretty at the top, just below the top of the 6m-tall mast, when using the inverted-L/7 configuration.

Of course, a 10m-tall mast would be superior, but also more heavy.

The measured distribution of the current or resulting magnetic field along the radiator wire can be seen in one of the referenced links that are contained in chapter 15:

On the 20-meter band, the radiator is one lambda long, so we have two areas of max. current: around 5m and around 15m. The 5m one is at the top, but the 15m one is already close to the ground.

About the bending of the wire: before I standardized on my “top radiator wire support”, which relaxed a bit the sharp bending of the wire, it seemed to me, that there were additional (near) resonances occurring. It would be interesting to see if somebody else already analyzed the effects of sharp bents in radiator wires.

73 Stephan

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Stephan @HB9EAJ thank you for the document and your work! :+1:

73 Marcel DM3FAM

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Hi Stephan,

Thank you for explanation, I now fully understand what you meant.

As for the bent angle, I read somewhere that we should avoid angles below 90deg. As we all know this is sometimes impossible to achieve unless you have number of suitable trees and plenty of time to setup antenna.

73 Marek

Another very interesting article on even more efficient winding style

https://www.kn5l.net/kn5lEfhwUnun/

If weather is bad this weekend I might try it out and do some measurements.

73 Marek

Simply brilliant !!!

73 de Dani EA5M

By the way. Where to buy the Fair-Rite 2643625002 toroid core ?

Mouser, Digikey, Farnell.

Also eBay vendors have them.

A Google search for “Fair-Rite 2643625002” gave me 6300 hits to many vendors.

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@SP9TKW

Yes, I read that too, but I never saw data that backs this up. Is 85 degrees already a problem, or 45 degrees? In the last European SOTA event, I used a second mast (see photo) that kept the angle at around 90 degrees

Indeed, this is a great idea! This article is linked from within the ferrite core transformer article.

Update: for a wide frequency range, the transformed impedance looks for both winding ratios very flat, which is very nice and much better than the typical transformers with the standard winding technique!
Of course, all has to be measured by connecting a real radiator.
What I’m struggling with, is understanding how the toroid core is exactly wound. I don’t understand or can’t really get the picture of the following two sentences: “Crossing over the windings inside the core forming a winding per winding interlace. Wind on six interlaces turns.”. What is or how looks the winding interlace and what are interlace turns? It doesn’t help me to use Deepl.
Anyway, I would be very interested in the outcome!

@EA5M As Andy @MM0FMF proposed, there are many sources to get them from. I looked for a local source in Switzerland, but finally bought 10 from Mouser, along with capacitors and other bits and pieces to avoid the surcharge. The delivery was exceptionally fast.

73 Stephan

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