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3 Band EFHW Trapped antenna


#1

Hi All

My last failed outing was a jaunt around Dartmoor mid Feb in the hope of getting up High Wilhays but wasn’t to be despite a two night wild camp on the Moor. Cold and deep lying snow made my intended route slower and more difficult for my short legged dog companion. So we didn’t get there in the end. Next time. Eny way I took with me in rather a hurry a 40m EFHW and MTR transceivers and did make a few contacts at night in my tent in sub zero conditions but as the MTR has three bands decided to build a multi band antenna for the next trip.
I like the EFHW for easy set up and operation so looked for a way of making it multi band. Two options being linked or traps. Links would not have the flexibility of changing band without messing with the antenna and having to leave a warm sleeping bag! So traps it is from SOTA BEAMS
I chose the pico traps built for 20 and 30m. Cut the wire for the appropriate lengths and attached the traps. All very simple. Testing in an inverted Vish deployment in the garden showed a good enough match using a SOTA BEAMS tuner on all three bands without the need to do any further adjustments.
Now for a return trip to Dartmoor!

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#2

Hello Chris you say you cut the antenna to the appropriate length to be a EFHW with the traps for each band I was wondering why you need to tune it as well. I assume it is hard to get a good swr or find a resonate point for each band . Be interested in what you found with the use of such a system.
Cheers
Ian vk5cz …


#3

Hi Ian

It’s also good insurance against a blown PA as each deployment will have different characteristics and and EFHW needs a matching arangment to present a low impedance to the TX. When testing in the garden it was windy and even the slight gust of wind was altering the vswr a bit. It’s a compromise but works and works simply. I’m not a perfectionist but just interested in a solution that works for me and hence didn’t tune the resonant lengthen to closely as it may be different next time I put it up. It was low enough 20m 1.2 to 1, 30m 1.5 to 1 and 40m 1.7 to 1. Not worried about that but could do a bit to get 40 down playing with the length I suppose. There again I could get it it matched better in the garden and find it worse in the field. Theoretically the lengths should be about right and the tuner compensates for field variances.


#4

OK thanks mate I find the same results with differing environments or summits and even changing frequency at times needs a re nip on the kx3. I just use 53 feet of wire end fed with 6 feet of counter poise and people are probably sick of me talking about my end fed. I do like the MT1 tuner by You Kits it has a built in swr metre and a good selection of inductance’s for tuning the 53 footer as well with the HB-1B.
Thanks for the response re your situation good information.
Regards
Ian vk5cz …


#5

I suppose here I am looking at what is effectively a half wave dipole just end fed so needs to be at a resonant length as opposed to random. So the 40m full length is around 20m then 30m is using 14m before the last trap and 20m is using the first 10m before the first trap.


#6

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


#7

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.


#8

Hello Cris

I have 2 spare pico traps…:slight_smile:
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


#9

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


#10

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


#11

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


#12

That’s something that I want to avoid.

73


#13

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


#14

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


#15

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


#16

Hi Ignacio

My traps are coated with liquiq rubber. It works fb and not detuning noticed!

73


#17

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.


#18

Hello,
Would you mind telling us the variable capacitor specifications or a picture or both?
Thanks a lot.
73 de Guru


#19

Hi Guru

A polyvaricon and a coil/toroid is thye way to go if you use QRP. :slight_smile:


or
http://www.aa5tb.com/coupler2.html
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!


#20

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:

  1. an End Fed antenna (EF), and
  2. 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