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A SOTA Centric End Fed Half Wave Antenna

I have been using end fed half wave antennas for the three years that I have been doing SOTA with satisfaction. I can count on 1 finger the only time I used a dipole. I just find it too annoying having to deal with the two legs of the dipole hanging with yet a third leg – the feedline, from the center point. The weight of the feedline can cause a mast to break at its weakest point. Stringing a dipole using a branch of a tree as a center support is also trickier.

With the end fed halfwave antennas (efhw), performance has been very repeatable, at least in my experience, with the true half wave end feds (not the shortened versions that uses coils to shorten the length of the antenna. After all the experience of activating close to 140 summits, I sought for a system that uses the bands I use to activate for SOTA, 60m for short range chasers trying to get completes, 30m and 40m for the intermediate range chasers, and 20m for the long-range chasers (coast to coast or transatlantic).

I could not find a single supplier that provides all these bands in one package and be resonant in all these bands without using a tuner. Not finding one, I made my own system which is as follows:

  1. A base antenna which is an end fed half wave on 40m
  2. A link that can be disconnected at the 30m halfwave point which makes it a half wave on 30m
  3. An extension which lengthens the antenna to make it a half wave on 60m

The base antenna is resonant on 40m, 20m, 15m, 10m, and 6m. Of these 5, I use 40m and 20m for SOTA.

The overall length of the antenna is about 76 feet or so – 10 feet longer than the 40m halfwave. The extension for 60m is made shorter by a 30 microHenry coil. For 60m it is very much acting like a low dipole with the apex at 20 feet. For 30m, it acs more like a sloper with the link near the apex. For 20m and 40m it is an inverted V, a half wave radiation pattern on 40m and two half waves on 20m.

The coil in the extension does not appear to hamper performance much. I was still able to do a 600 mile summit to summit QSO with WB2FUV who was in the Catskill Mountains in NY and I was in on the Appalachian Trail on the summit of High Rock W4T/SU-024.

Here is a picture of the entire antenna system which uses an integrated transformer and winder. The transformer box has a single FT140-43 ferrite core wound with 14 turns secondary and 2 turns primary for a turns ratio of 7. The impedance transformation goes as the square of the turns ratio – hence an impedance transformation of 49:1 from 2450 ohms to 50 ohms. The power handling capability is 60W SSB, 38W CW according to the paper written by K1RF. I have not had any issues running it at 80W chasing activators from my home but I only run it at 5W when activating. There is a lug for an optional minimum 1/20 wavelength (on the lowest band) counterpoise.

With extension for 60m I measured an impedance at the feedline of 39 ohms for an SWR of 1.2. The 2:1 SWR band width is >200 kHz and more than broad enough for the narrow allocation of channels used on 60m. This is shown by the image below:

Picture2

The usability on the other bands can be made without using a tuner. On 40m the bandwidth is quite broad with an SWR of 1.3 on the low end at 7000 kHz rising to about 1.7 on the upper end. I have constructed 30 of these and these values are reproducible. The worst I saw on 7.30 MHz was an SWR of 2:0

Picture3

40m SWR Sweep

On 20m and 15m, it is very broad-banded with the 2:1 bandwidth in excess of 350 kHz on 20m and greater than 500 kHz on 15m.

Picture5 Picture4

The other highly used band is 30m which if tuned properly is literally flat across the tiny 50 Hz allocation of the 30m band. 10m has an acceptable SWR between 28 and 29 MHz and usually rises to about 2.3:1 to 2.7:1 SWR above 29 MHz.

Picture6

In one neat and tiny package (less than 9.5 inches length) and less than ¾ of a pound – I have an antenna system that fulfills my needs for SOTA activation. I typically deploy as an inverted vee. Inside the box is the transformer with two 220 pF high voltage capacitors in series across the primary.

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Ariel,

Your nice looking EFHW Antenna could easily be made more efficient if the 1:49 impedance transformer were wound with 3/21 instead of 2/14 turns.

If the transformer is only used with transmission powers up to max. 15 W cw/ssb and 10 W data, more ore less the same efficiency could be achieved with 2 stacked FT-82-43 toroidal cores.

BTW, impedance couplers 50:2450R (1:49) can of course also be used with an 80 m EFHW Antenna, but because of the low inductance of this coupling ratio, no sufficient coupling does result (SWR> 2).

Edit 09/01/2021
The title in my original post was possibly misleading because the calculated efficiency values ​​in the table are not dependent on the coupling ratio.
Therefore “50:2450 ohms (1:49)” was deleted from the title and the comment for the 80 m band was adjusted accordingly.

4 Likes

Good stuff, endfed antenas are dipoles, just fed at the end instead of the middle … my endfed has served me well.

ed

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Glad to hear you have an antenna that meets your needs.

BTW if your mast breaks under the weight of the feedline you need to use a thinner coax. The extra losses on hf are small.

I have a philosophical dislike of using the feedline as part of the radiator which is the case in most EFHW.

I prefer to take a doublet and ATU for all band operation from the operating position.

If I want a lighter antenna system then I take a link dipole and accept the slower band change over.

If an EFHW is efficient then resonance will only occur on one band. For other bands the SWR may be 2:1 at the operating frequency. Not that that is a problem, but this is the point at which most rigs start folding back the power.

73
Ron
VK3AFW

Sorry, the title in my original post was possibly misleading because the calculated efficiency values ​​in the table are not dependent on the coupling ratio.
Therefore “50:2450 ohms (1:49)” was deleted from the title and the comment for the 80 m band was adjusted accordingly.

Looks great! Don’t you just love a simple, lightweight, and small (when wound) antenna that gets you on multiple bands from a summit? Makes the EFHW a very popular choice. I hope to work you on that wire!

Thanks for sending the table and helpful suggestions by HB9CB. I will build also a version with 3 turns primary and 21 turns secondary to see if I can improve the efficiency. i will compare the results with the activation I did at W4T/SU-024 on 20m and 60m. SMP provides a graphic of the QSO’s made from that day on 12/29/2020. The results include 3 transatlantic Q’s on 20m and an S2S with WB2FUV on 60m over a 600 mile distance.

Ariel NY4G

N4HNH made a YouTube video from the activation he and his brother Wayne W4KWM from North Georgia using the antenna I made for Wayne. They were both running 45 watts using an FT891 and SSB. The video may be found at this link https://youtu.be/Cz63h7TLCyQ

The SMP “reach map” for W4WKM on 60m SSB is below

N4HNH operated on 20m also at 45W SSB. Max distance was 2085 miles.

.

Scott KW4JM took this same antenna system I made for him on a three day backpacking adventure on three summits in the North Georgia mountains and yielded 5 DX contacts including one with ZL1BYZ, and 8 S2S’s, and 108 QSOs.

Ariel NY4G

1 Like

Ariel,

I’m very interested in your linked EFHW antenna design. Glad to be part of the experiment.

Regarding our December 29th s2s QSO on 60 M band, I was not in the high peaks of the Catskill Mountains but instead on W2/GC-075 (Spy Rock, elev 443M) in the Hudson Highlands above West Point, NY. My rig was FT-818 at 6 watts. The antenna was an inverted vee 40-30-20 linked dipole up about 20 feet with legs N-S using clip-on pigtails for 60M.

Thanks for the s2s from a lowly 1 pointer on 60M.
73!
Mike, WB2FUV

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Mike WB2FUV

Thank you for that 60m S2S. That was my first S2S on 60m. It may have been a lowly 1 pointer for you but it was exciting for me to get an s2S on 60m in any form.

Ariel NY4G

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At the suggestion of HB9BCB, I built another transformer with 21 turns secondary and 3 turns primary to see if I can realize a small gain in efficiency. I don’t know of an objective way to measure this in reality other than to use the Reverse Beacon Network.

What I did is I used the same antenna wire - but alternated between the two transformers. It is still the same turns ratio but the dips moved around a little bit. I chose 60m for the test 5.332 and 5.373 MHz running 5 watts on an inverted V. On the 14/2 transformer, the sweet spot of the dip was right at 5.332. On the 21/3 transformer the dip has shifted to below 5.332 MHz and I was at 1.9:1 SWR at 5.332. So I will have a little more reflected power and perhaps more feedline losses.

The results of the experiment:

I started out on the 14/2 and 3 RBN stations responded. I QSY to 5.373 and shifted to the 21/3 transformer. The same three stations reported with an improvement from KD7YZ and W3OA-2 and 2 dB worse from K9IMM. This is just 1 data point from two transmissions a few minutes apart.

I checked the rest of the bands and i will have to shorten the antenna and 60m extension to re-optimize for the 21/3. in general, the SWR is lower by a tenth or 2 tenths with the 14/2. But if the efficiency is real i will rather switch to the 21/3. Thanks to HB9BCB for the tip. I computed my radiated power accounting for feedline power losses and it looks like I gained about a 1/2 watt. Once I re-optimize the antenna length, I will have gained 8/10 of a watt.

Ariel NY4G

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Dear Heinz,

Very detailed and useful table!

Maybe you’re interested to add a Fair-Rite 2643625002 core that I use for my EFHW QRP antenna experiments, since I saw an article from Owen Duffy at https://owenduffy.net/blog/?p=12642 and a YouTube video at https://www.youtube.com/watch?v=AjH1iesDWJI.

With 3 primary windings you’ll get over 90% efficiency (because of its different geometry), which I calculated with the same calculator you used:
toroid-efficiency

Also, your coupler design, that I found in this forum, inspired me a lot!

I’m creating a document with all my ideas and results for a unique EFHW antenna design that I never saw before (7 Bands, including 60m with 20m wire length), inspired from many sources, which I want to share with the community. Unfortunately, some data is still missing and things need more time than predicted…

73 Stephan

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Ariel,
Great discussion! One item not mentioned above: What is your type of feedline and length of feedline?
Thanks and 73!
Mike, WB2FUV

Thanks for the message, Stephan.

Yes, this toroidal core from Fair-Rite is well known to me and has been in operation in my couplers since spring 2018. Such couplers with different coupling ratios for different needs are also in operation at some of the SOTA colleagues I have supplied, hi.

The reason for this is that I had the courage (…) to contact Owen Duffy when he published the first post on this topic on his blog. We then corresponded with one another while looking for a more suitable toroidal core and exchanged test results.

Sorry, that’s why this is no longer a new discovery for me and I am not just, as some seem to assume, only focused on EFHW couplers and antennas. This is mainly because I have not been allowed to set up an external antenna for almost 45 years and thus automatically indulged in portable radio.

BTW, what you don’t see or only rarely see here on the SOTA Reflector is a discussion of the radiation properties (e.g. elevation) of the (highly praised) dipole antennas on the short masts usually used for SOTA (typically 6 m) .

73, Heinz






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Thanks for the interesting info in this thread, to be considered for building better couplers in the future…
A lot to learn from Owen Duffy.

73 de Ignacio

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Sorry, I actually wanted to include this information in my last post:

You should be prepared for the fact that increasing the turns ratio of your 1:49 impedance coupler from 2/14 to 3/21 turns increases the inductance of the coupler, which leads to an electrical lengthening of the antenna (lower resonance frequencies).
For this reason, simply exchanging the coupler types on one and the same antenna and comparing the measurement results (e.g. SWR) on one and the same frequency will not produce a correct result.

With a little luck this can only be achieved by shortening the antenna on the coupler side. If that were the case, an extension piece (photo) could simply be looped in and out to compare the two coupler variants.
An extension is probably more welcome on the harmonic bands because the lengths for it are not exact multiples of the length of the basic frequency.

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Heinz,

You are indeed correct. I had to shorten the extension for 60m. It is harder to find a good balance between 40 and 20 with the 21/3 versus the 14/2. I think I found a solution I can live with but it needed several pruning trials best balancing the bands.

I have a wire set dedicated just for the 21/3 coupler.

Ariel NY4G

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Mike I used 10 feet of RG174 as a feedline.

Ariel

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Heinz,

Thanks for your clarifications.

I was not aware that you also experimented with the 2643625002, which shows a bit better efficiency than two stacked FT-82-43.

I see that you also tried the slightly bigger core 2643626302 that apart from its bigger surface and therefore higher power rating seems otherwise pretty similar to the 2643625002, correct?

BTW, you made beautiful couplers!

According to your last image, it looks like you measured a whole bunch of 2643625002 cores and came to the conclusion that their permeability has a tolerance of +/- 25%, which is quite a lot. I wonder if you measured this tolerance within the same batch of cores?

To be honest, after I read some articles from Owen Duffy, I realized that I was lacking a lot of knowledge in some fields, but thanks to the Internet, one can always learn.

And yes, the radiation pattern of a portable antenna is another important attribute. After playing with some models, in theory a vertical antenna would be much better suited for DX than a (mostly) low hanging horizontal dipole.

My personal compromise (ease of setup and no radials) is to configure an EFHW antenna as inverted-L (or more realistically an inverted-7), like that I still get a part of the low angle radiation from the vertical part and the pattern looks a kind of a heart :yum:.

One has also to be realistic: The conditions are so much more important than loosing some dBs, e.g. I can hear the same chaser with more than 60dBs variation in signal strength (if one S-unit corresponds to 6dB), sometimes even during the same activation. But on the other side, I like to optimize my setup for maximum efficiency, which to me is also part of the fun.

@NY4G Thanks a lot for sharing your experiences and measurements!

73 Stephan

Ariel, considering the usually rather short cable lengths of approx. 2-5 m to feed the portable EFHW antennas I don’t quite understand why cable losses are an issue for you.

However, we can only hope that the calculator used is not based on an antiscience algorithm, as Owen Duffy calls it in the conclusion of this article:

BTW, the difference in calculated efficiency for the couplers with 2/14 and 3/21 turns will only effect a fraction of an S-unit at the receiving station and will be therefore hardly noticeable subjectively (in a blind test …).

However, if a signal at the receiving station is only just above the noise level, this may very well contribute to the legibility of the signal.

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