Because the use of traps those dimensions are not exactly as in “pure” dipole.
I arrived to this conclusion - everybody said this will happen - by tweaking a 20/30/40 m trapped dipole. You can see this dipole at
73 de Pedro CT1DBS/CU3HF
You are right Pedro and they are just approximate as I can’t remember the exact lengths without looking them up. Still it works and tunes on all three bands and that is the objective…
Just looked them up.
20m 10.1m
30m 14.2m
40m 20.3m
As recommended for use with the mountain tuner.
So first trap for 20m at 10.1m second trap for 30m at 14.2m from the feed point followed by 6.1m.
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Hello Cris
I have 2 spare pico traps…
My goal is to avoid - as much as possible - to carry an ATU.
So, what is the length of the counterpoise ? Did you try with different sizes of counterpoise or did tried to “fine tune” the counterpoise?
Any thoughts ?
Tnx es 73 de Pedro, CT1DBS
Hi Pedro
No I haven’t tried to fine tune it as I always expect it would use a tuner and the impedance to high not too. The counter poise is only 2m long. My objective was to build a simple multi band antenna without the need to physically change any part of it when swapping bands.
Cris
Thank you for your answer. All texts talked that the counterpoise should be 0.05 of the wavelenght (the longer one, in this case).
However, I use a EFLW with my KX-3 ou KX-1 (both with ATU) without a counterpoise and about 9 m of rg-174. It work FB!
I even tried with counterpoise but not I didn’t noticed any difference. So, no counterpoise…
I bought a MTR-3B which is the core of my “HF pocket station”. An ATU will be too much!
That’s why I did the dipole with pico traps. I think that I should try a EFHW. We will see.
73
This is our antenna for 40-30-20-15. No tuner, no traps.
But lower and erect again at every bandchange.
http://www.ha5lv.hu/sota/belsolinkek/4band_dipol.html
73 Viktor HA5LV
That’s something that I want to avoid.
73
Hi Pedro and Cris,
You can build and use a multiband EFHW (end fed Half wave) without a Tuner.
To get rid of the tuner, all you need is:
- properly cut lengths of wire and add links or Traps (as you have already done), and
- prepare a proprer Feeder: this is what I think you don’t have.
Without the feeder you will always need the Tuner to do the job of reducing the impedance of the Half wave (about 3000 ohm) to 50 ohm of your radio.
Instead of the Tuner, I recommend to prepare an easy all band Feeder for Half wave antennas.
This is a very good feeder:
For QRP power levels you can prepare it with T82-43 toroid or 114-43.
II use that and it works FB.
All you need is the toroid, a 100 or 150 pF capacitor (1000 Volts) and enameled wire (0,5 mm diameter).
See this minimalist feeder I have:
The capacitor is in the back side.The Coax is 3m of RG-174.
Concerning counterpoise, you don’t need any if you use enough coax of about 3 or 4 meter between this feeder and your rig. The braid in the coax performs the function of counterpoise.
IMPORTANT: you have to keep ends of the Half wave up over ground. If installed as Inverted Vee elevate the feed point over ground 1 meter. Sometimes in certain summits you have to move operating position or wire to get better SWR by extending the coax.
Many people use end fed with a tuner, installed at ground level. Try this little feeder and you will reduce a lot of weight!
I’m uising the 10-20-40m since months and never had any SWR problem. And log a lot of stations or even VK S2S when propagation is fine…
EFHW, what else?
Take care 73 de Ignacio
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Hi Ignacio
Thank you for quick reply.
I’ve built one of those. It works with my EFLW.
What I didn’t tried is to cut a proper length of wire and/or add the traps. That’s my next step.
The wet WX doesn’t affect performance ?
73 de Pedro
Hi,
I didn’t notice weather troubles with my EFHW, but I have a waterproof feeder (in a plastic box) for winter, and I don’t have traps but the coil showed in the web link for 40m band.
If I had traps I would cover them with liquid silicone…
73 de Ignacio
I have a similar matching tuner to reduce the impedance down to 50 ohms as you describe. It has a variable capacitor to match different half wave lengths of wire. Using the traps just means I don’t have to change the wire length but just adjust the capacitor. Very simple and no need to play with links or take the antenna up or down. Still need to waterproof the traps.
Hello,
Would you mind telling us the variable capacitor specifications or a picture or both?
Thanks a lot.
73 de Guru
Hi Guru
A polyvaricon and a coil/toroid is thye way to go if you use QRP. 
or
or (Spain)
http://ea3gcy.blogspot.pt/2014/04/ilertenna-end-fed-qrp-antenna-tuner.html
73 de Pedro
BTW: TNX fer QSO on CT/BA-002!
Hello,
these qrp tuners are nice.
Just to make sure we don’t get mixed with concepts let me say: there are two different antennas we call similarly while they are different.
I see many people talk about End fed as if it were an EFHW while it is not.
Both antennas have something in common; they are fed at its end:
- an End Fed antenna (EF), and
- an End Fed Half Wave (EFHW) antenna.
The first type, could be either a random lenght of wire used for multiple bands with the aid of a tuner, or It could only be resonant at a single frequency. The function of the Tuner is to compensate the mismatch between the antenna impedance, far from your desired 50 ohms. You can use it multiband but performance will vary from band to band.
The second type is cut exactly at half the wavelength of a frequency. It requires the type of feeder I mentioned in my post (or a similar transformer).
You could use some of the tuners like these shown before for an EFHW, but it is not really needed with a proper feeder: you save weight and tuning time. Of course, you could still use such Tuners with an EFHW to compensate slight deviations of impedance if you want to ensure a 1:1 SWR value, although benefit is small.
Then, if you want a multiband EFHW, you need such traps or links in the wire to ensure you always have Half wave for the band of choice. The performance at any band is exactly a Half wave antenna.
Usign the traps in an EFHW is nice as you are changing the antenna lenght automatically and instantly.
Both antennas work. The question is to choose what you want to carry in your rucksack and how to setup up in the mountain.
73 de Ignacio
Hi Ignacio
Absolutely right.
I want to use the EFHW with the MTR-3b to avoid carry the ATU, i e, be lighter.
I’ve made a trapped dipole but in some summits the space is not that much…
73 de Pedro
PS - TNX fer QSO on CT/BA-002!
Hi Pedro,
hope you will enjoy with your small setup soon, it is a nice compact system!
Thanks fer BA-002, glad to have a CT CW activator close to us 
73 de Ignacio
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I too use and like the broadband matching network approach to EFHW antennas. I have a 5 band trapped EFHW which I find works very well on the whole. Details and dimensions are on my blog:
Anyone interested in broadband matching networks of this type may also be interested in Owen Duffy’s analysis - they’re not simple transformers!
http://owenduffy.net/blog/?p=7073
73
David
VK3IL
Hi David,
thanks for sharing the interesting link with detailed information.
Did you know I found your design some months ago and I am building a replica nowadays here? Funny coincidence.
But I’m trying to combine it with coils to avoid making it so long for 40 meter… Difficult task!
73 de Ignacio
Hi Ignacio,
Pleased to hear you found the information useful. To shorten it on 40m, perhaps add a 20-30uH coil after but fairly close to the last trap (i.e in the 40m only section of wire, but as close as possible to the current maxima). Then trim that last section to resonance. I’d try and model it in NEC2 first though. You’ll lose some efficiency of course, but would be interesting to see how it performs.
73
David
VK3IL