Trapping the End Fed  Antenna

The End Fed Halwave antenna is a resonant antenna cut to the band you want to use, unless you add traps= Multiband.

I have been using my Packtenna End Fed Halfwave (EFHW) antenna for several years now and have over 300 QSO’s / 39 activations using this antenna. As I have been doing more SOTA activations with the focus on CW, I primarily use my Mountain Topper 5 band HF QRP radio. Since this rig lacks a tuner (unlike my KX3), I use the EFHW as my go to antenna. A dipole comes in as number two.

Featured Project

Building Custom Antenna Traps

While the EFHW is a resonant antenna and in my case, cut for the 20 meter band, I do like to utilize other bands. There are two major ways to accomplish this.

 

 The first method I used was to unsolder the factory antenna wire and solder on 2mm bullet connectors on wire elements cut for each band. In my case I had a 20 and 40 meter resonant wires that I could switch out depending on what frequency I was using. The downside of this is that it takes time and tearing apart your portable antenna setup is not desirable on top of windy summit. Which leads to method number two: build and use traps.

Review of the Packtenna Antenna systems in the November 2016 QST magazine.

QST magazine

Installing traps on an antenna allows you to turn your EFHW into a multiband antenna. When you switch bands on your radio, the antenna is automatically set for the band you have chosen. No need to pull the antenna or change elements. As far as traps go, you can buy them online or make them yourself. Since we are talking portable operating and backpacking, weight is a concern.

While checking out OSHPark a few years ago, I stumbled upon the WS0TA PCB traps. These allow you to choose your own capacitors and inductors based on the frequency you choose. There is some RF magic voodoo theory and testing going this route.

*Note: That is not Fred , KT5X. Fred is way much cooler than that.

The WS0TA traps were designed by Fred Maas, KT5X and Rex, KE6MT two very experiencied SOTA operators worth checking out. Rex has a link to a very detailed pdf that Fred shared with him which includes not only building traps but also sone interesting antenna ideas as well. 

Adam, K6ARK another SOTA operator, did an excellent video on building traps for an end fed antenna. Well worth checking out:

One of the first things I did when the bare PCB’s arrived was sand down the height of the board from 6.41mm to 5.63mm. The reason I did this was once the toroid was wound, the PCB was too tall to fit inside the toroid with out moving the coils around.

Measuring the trap
Building End Fed Halfwave antenna

 Taking the toroid’s I wrapped it 40 turns on the T50-2 (20 meters), and soldered in a 15pF capacitor (650 volt, 1206 SMD, NP0) in parallel. I covered the whole thing in shrink wrap. I later made a 3D printed cover for it but found it really wasn’t necessary. I didn’t have high hopes that the trap only covered in shrink wrap would withstand being dragged through the mud, snow, sand and being repeatedly wound on and off a Packtenna winder.

I was wrong, as two years later and after many activations it is still working the same as the day I installed it. Recently when I was section hiking the Long Trail in Vermont, I used this antenna extensively. The one issue I had was only 20 and 30m capability; I really needed 40m and possibly a higher band like 17m. Currently I am collecting parts to build a 17, 30 & 40 meter traps. Parts are on order and I will update this entry with my findings.

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