Trapped end fed half wave 20, 30, 40 m

Hi all

I made a nice EFHW using Sotabeams pico traps.

Nice bandwith, nice performance on air and yet very light. :slight_smile:

73 de Pedro, CT1DBS/CU3HF


Nice write-up Pedro.

I’m making one too. I just need a chance to tune it up. I’m using wire from Richard as well, but the reinforced DX-wire (it’s a bit heavier I think). My fishing pole is a 5-m Ron Thompson travel pole; this packs away to 0.62m. I was originally going to make my own traps but the SOTABeams pico traps are great.

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Nice set-up. I always used a linked dipole, it is a great antenna but you need to bring it down to change bands.

I will start using a 1/64 balun with 20mtr of cable made by my friend OT6V, no traps. Works as a charm, swr is 1.3/1 on all bands or less. Can be used on 10mtr, 15mtr, 20mtr, 40mtr, and with a tuner also on 30mtrs.
Cost of it all…20euro. Quick band changes are no problem anymore :slight_smile:

With my KX-3 I used a “long wire” end fed.
The wire is as long as possible (less than 35 m) in the summnit and I tune it with the KX-3 ATU. It works fine!

But I’m looking for something that allow to use the MTR without any ATU: The simpler and ligther HF station… :wink:


Welcome Pedro in the club of trapped end fed wire antenna builders!

BTW, your antenna would not be called a true EFHW by antenna purists because the 1:8 Unun (50:400 ohms) does not match the typical impedance ranges of EFHW antennas. Don’t worry about that and have fun with your tuned trapped end fed wire antenna.

Pedro, why on earth do you elevate the non radiating end of the antenna (no current/no radiation)? Using a short 2-3m coax to the coupler and then elevating the antenna wire as inverted V/L or as a sloper wire will radiate the most efficient way. Besides that the lengthy/lossy/weighty 8m coax may be omitted, hi.

Hi Heinz

TNX for your comments.

I didn’t know of such club but thank you for the warm welcome! :slight_smile:

Well, purists…I’m not!
I must to explain it better. It’s an impedance transformer with the ratio of 1:64…The references of some other OMs that “paved the way” are in the article to enlight this.

I believe that the radiating end of the antenna is the one far from the feedpoint.
The lengthy/lossy/weighty cable (RG-174) avoid me to do not use a counterpoise.
With the MTR is use a less lossy lenght of rg-174: 5m.

Anyway, I try it in the past (EF “long wire” with ATU) and it works flawless.
I try it again last Sunday (this set) and it worked.
Well, if it works…

And, like you say, one must have fun!

CU es 73

I made also one for 40m/30m/20m/17m developed and described in here from HB9TVK

good luk Peter/HB9CMI

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Ok then, Pedro.
Please note that the usual denotation for Baluns and Ununs is by their impedance ratio (e.g. the well known 1:1 and 1:4 Baluns and the 1:9 Unun) and NOT by their turn ratio!
If the impedance ratio of your transformer is really 1:64 (turns ratio 1:8, e.g. 3t primary, 24t secondary) then you could/should call it an Unun 1:64.

Regarding this, your documentation showing an 1:8 Unun is misleading/wrong.

Please note that the maximum current/radiation appears in the middle of a half wave antenna and there is no current flow/radiation at its ends.

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Hi Peter

The braided fishing line is a very neat idea! :slight_smile:

TNX for the link.