20/30/40m trapped end fed. Nice!


Because of the purchase of the MTR-3B, the ultimate portable HF radio, I decide to make the lighter station as possible.

So, I have the MTR-3B, the Pico Palm Paddle, a small pack of NiMH batteries. I miss a friendly antenna that could transported in a small bag.
The trapped dipole and a light phishing pole were the solution !

After a few activations with this set I wonder if I could make it simpler.
The dipole needs to be in rolls to transport, so, why not a light “one-roll” antenna ?
Why not an EFHW ???
I don’t want use an ATU. So, it should be ressonant.

Based on a 1:8 Unun (offer of CT1DTE) I decided to try it.

On the sunny afternoon of sunday, Sept 18, at my brother-in-law home (wonderful place near river Vouga, Aveiro), I installed the pole and the wow factor started to appear…
The trapped EFHW work flawless and the bandwith is great.

As usual, I used Sotabeams pico traps. They’re great! 🙂

And light (5 gr) and small:




I started with the 20m band wire. I made it long…

After trimming, the length is 9.9 m including the turns for the banana jack (unun side) and turns for tie and solder (pico trap side).

The SWR, measured on the antenna analyser of my friend CT7ABE, is the following:



Great start! 🙂

Then I installed the 30 m band pico trap. After soldering it to the 20 m band wire, i started triming. Always make it longer….

I notice something interesting, that I noticed as well when I builded the trapped dipole. The measure in the 20 m band doesn’t change. This is good because it’s much simpler to build such antenna.

So, after trimimg, the wire length is 3.4 m, including the turns for tie and solder (pico trap side). The SWR is:




So far so good!  SWR stable in both bands. So let’s solder the 30 m band pico trap.

Again, I noticed the measure in the 20 m and 30 m band doesn’t change.

Good job Sotabeams! 🙂

So, after trimimg, the 40 m band wire length is 5.1 m, including the turns for tie and solder (pico trap side) and a small loop to attach the antenna to a rope.

After trimming the 40 m band wire, the SWR is:



I double checked the SWR, just in case, but everything is ok. 🙂

So, I connect the Elecraft KX-3’s BNC to the RG-174 and we are on the air. Some QSO were made with good signal report.
I even tried to tune the KX-3 on other bands, with the help of the internal ATU. Success!

It’s nice for the MTR-3b but it can be used with other rigs and frequencies, if an atu is avaiable.

The final dimensions of the end fed half wave (in 3 bands) is :



Final dimensions


2 photos of the testing of the actual antenna



To tie the wire to the pico traps I used heat shrink sleeving.
This is more than enough to have a loop in the trap side and do not stress the trap’s PCB.


The traps before coating with liquid rubber



A trap after coating, i e, ready to go!



The wire is also from Sotabeams (yellow hi-viz).


Unun 1:8

Like the one of PA3HHO or the one of N4SPP but made by CT1DTE, Luis Valadas.

The end fed halfwave connects mechanicaly to the UNUN as follow:




Phising pole

6m pole. Only 5 m usable (top section to thin).

From Decathlon, Pole 600 Carpelan

Nice, cheap and durable.


The pole in a rainny activation


8 m of good quality RG-174U.
BNC’s from Amphenol.


It seems that my portable portable SOTA station is lighter and more and more transportable, below 1 kg! 🙂

Big thank you to CT7ABE and CT1DTE.



  1. f4eed · July 17

    Reblogged this on f4eed – petit mémo V4 and commented:
    20/30/40m trapped end fed. by Pedro, CT1DBS/CU3HF


  2. Pingback: Une antenne pour mon MTR-3B – F5NFB

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s