Putting the KM4ACK End-Fed Half-Wave on the air at Table Rock!

Lately, I’ve been in the mood to build kits.

I say “lately” but in truth I’m always tinkering with something in the shack.

The radio room/office at my QTH is pretty small, though, and I don’t have a dedicated, full-time workbench. I’ve been mentally re-arranging the room and trying to sort out a way to make space for one because it would be so nice to have a spot where my soldering iron could remain hooked up at all times.

For the moment, when I work on kits I use our dining room table so I try to stick with one or two session kits as opposed to the multi-day variety.


KM4ACK Image

A number of readers and subscribers have asked me to check out the KM4ACK 49:1 End-Fed Half-Wave antenna kit.  This kit is produced by Jason (KM4ACK) and purchasing his kits supports his excellent YouTube channel.

I have a lot of field antennas, so I don’t really need another EFHW, but then again I like having a dedicated resonant wire antenna with each of my radios and, (hey hey!) it’s a great excuse to build a kit!

KM4ACK Image

I purchased the KM4ACK kit and received it within a week. Building the antenna was incredibly straight-forward. Jason packaged the components in small bags so finding parts was easy. I really appreciate kits that aren’t one large “bag-o-parts.”

The kit doesn’t ship with a printed guide to building the antenna, but it does contain a link to an excellent video Jason made which walks you through each step of the process.  This was the first time I’ve ever built a kit from an instructional video. In truth, I’m a bit old-school with my kits and prefer printed manuals, but I must admit that for a super simple one-session kit like this? The video worked exceptionally well.

This is a great kit for a beginner, too. There aren’t many parts and 49:1 is super easy to wind.

One small snag…or so I thought…

The antenna kit ships with a slightly longer wire than you need for a 40M EFHW. This is expected with an antenna kit because once the antenna is built, you simply deploy it outside and trim the radiator to be resonant where you operate on the band (a bit longer if you’re a CW op and a bit shorter if you’re SSB only). In truth, EFHW antennas have a pretty wide resonance area on the band, so it should easily cover both the CW and SSB portions with an acceptable SWR.

Thing is, while building this antenna I accidentally cut off a good portion of the wire while clipping a cable tie. I’m guessing it was about 2 feet or so. I have a plenty of wire here at the QTH to replace that which Jason provided, but since I’d already crimped off the ends and built the strain relief, I was already committed to the yellow wire provided so thought I’d give it a go anyway.

When I deployed the antenna for the first time at the QTH for testing and trimming, I used my new RigExpert antenna analyzer for the first time. The EFHW appeared to be resonant slightly above the 40 meter band. That would make sense since I’d accidentally trimmed off too much of the wire. I thought I was getting a 1.8:1 or 2:1 on 40 meters.  I decided I’d simply give it a go on the air regardless and possibly use an ATU to tweak the match, then in the near future replace out the radiator.

With a completed EFHW, I only needed to take it to the field so that’s exactly what I did the following day (October 27, 2021). I also had a park in mind!

Table Rock Fish Hatchery (K-8012)

Table Rock Fish Hatchery is an ideal park to try out a new antennas: it has large trees, lots of space, and there are no visitors running around to get tangled up in my wires and lines. 🙂

Deploying the KM4ACK EFHW was easy enough: I launched one line into the tree and pulled the radiator over a limb to form an inverted vee shape.

I actually show the full antenna deployment in my video below (less about 5 seconds I accidentally clipped while merging two of my video files together).

I also brought my Icom IC-703 Plus along for this activation. It’s been ages since I’ve used in the field and, especially, in one of my activation videos.

Thing is, once I hooked up the IC-703 to the antenna and tried keying, I found that the internal electronic keyer wasn’t sending accurately. After scratching my head a bit, I have to assume that there was some RF coming back to the radio despite the fact my feedline has an in-line RF choke. Perhaps the IC-703 is super sensitive to RF? I’m not sure what was happening.

I hadn’t had this problem before but didn’t want to spend too long diagnosing it in the field, so I pulled out my trusty Elecraft KX2.


On the air

After hooking up the KX2, I was pleasantly surprised to find that the antenna was perfectly resonant on 40 meters.

It then hit me that perhaps I wasn’t reading the RigExpert correctly when I tested the antenna at my house. I did, after all, use the RigExpert for the first time without reading the manual. (Learn from my mistakes, will you?)

Good news was I didn’t have to replace out the radiator with new wire and instead I actually had a near 1:1 resonant antenna almost by accident. Woot!

I hopped on 40 meters and started calling CQ POTA. The Reverse Beacon Network found me and the POTA website scraped my information and auto-spotted me.

Within 9 minutes, I worked 10 contacts, validating my POTA activation. It doesn’t get much better than that!

I continued working stations on 40 meters until I had logged about 22 in twenty minutes.

I then moved up to 20 meters where the EFHW was also perfectly resonant and worked an additional five stations–including a Park-To-Park with N7OOS (thanks!)–all in nine minutes.

Not bad at all!


Here’s a QSO map showing what the KM4ACK EFHW did with 5 watts that day during a short activation:


Here’s my real-time, real-life video showing the entire activation. This includes a lot of extra footage, so you might prepare a cup of coffee or tea!

Click here to view on YouTube.

Final thoughts on the KM4ACK EFHW kit

There are good reasons the EFHW is such a popular field antenna design: it’s efficient, it’s resonant, it’s easy to deploy, it’s relatively compact, it’s affordable, and very easy to build!

If you’re looking for a simple EFHW kit, I can recommend the KM4ACK version without hesitation. It’s quite affordable ($39 US). I really like the antenna winder and how he’s implemented the BNC connector. Also, the video guide to building his antenna is clear and easy to follow. There’s no guess work in this kit.

If I have one concern, it would be that I do fear I may damage the exposed 49:1 coil/magnet wire during deployments and while in my field pack. I tend to be pretty rough on my gear especially as it shifts around in my backpack while hiking, etc. I’m going to think about how I can protect the coil better and would welcome your suggestions. I did take Jason’s advice and encapsulate the back of the BNC and connection wires with hot glue which I would certainly recommend as well.

Thank you

I hope you enjoyed coming along with me on this activation and antenna test!

When I first started making real-time, real-life videos last year I would literally press “start” on my iPhone and record an entire activation in one large video file. I did everything I could back then to avoid having to do any post-processing work in a video editor.

Today, I primarily use an action camera that records my long videos in 2GB chunks. At first, it annoyed me that I would have to dump all of video file segments into iMovie in order to produce one file I could then upload to YouTube when I had the bandwidth. Over time, I’ve gotten used to this process, though and have even recently upgraded to Final Cut Pro (thanks to your generous support!). While I still don’t deliberately edit anything out of my videos, and I don’t care to add any flashy effects, I do appreciate being able to add proper titles, comments, and even adjust things like audio when needed. Plus, Final Cut Pro is a solid application–I love it.

As I was putting together this video, for a millisecond I thought about excluding the part of the activation where I decided not to use the IC-703 Plus. It would have been effortless in Final Cut Pro.  Then I quickly came to my senses because, frankly, what I’m doing here is showing you what actually happens in the real world. Sometimes? Things just don’t work as they should, and we must adapt.

No matter what happens in the field, I’ll continue to show you the whole picture. [On that note, wait until you see the one where I activate Mt. Mitchell with the QCX-Mini! Spoiler alert: Insanity!]

A special thanks to those of you who are supporting the site and channel through Patreon and the Coffee Fund. While certainly not a requirement as my content will always be free–I really appreciate the support. I’m currently plotting a few upgrades to my field video equipment that should improve both the video and audio quality. Your generosity helps make that a reality.

Thank you!


Thomas (K4SWL)

9 thoughts on “Putting the KM4ACK End-Fed Half-Wave on the air at Table Rock!”

  1. Thank you. Interesting as I have that antenna just haven’t deployed it yet in the field, soon I hope. It seems to be a nice field antenna. I used the hot glue suggestion. I’m not great with kits and windings, however, I was able to getvthis together, and yes, With his video.
    Thanksgiving though I’ll head out to a park and attempt to use an old Silvertip vertical I purchased a few years ago and never used. Again thanks for your words of advice.
    73. WB8YXF

  2. I have already sent an email. Shows currently out of stock. Can’t wait to try it. Thanks for great review de W0HL

    1. Put your email on the list, and he will email you when they’re in stock, then order immediately as the stock doesn’t last long.

      1. If you want a X6100 then need to get your order on the list. If wait for stock then those that ordered will be first.

        My order is on the second batch.

        73, ron, n9ee/r

  3. IC-703 is very sensitive to RF. Try to connect ground of key socket directly to circuit board. Following is only in Japanese but I think you can have an idea of what I’m talking about. This really worked out well with my 703.

    Thank you for great articles and videos!! I enjoy them all.

    73 Masa KH6/JP1ITN

  4. Hey Thomas,
    Read your post and watched the video. To solve the durability concerns, I used a “Ranger Band” (Also known as a bike tire tube) to cover the entire winder board and parts. Get a large bike tire tube (2.4” width) and stretch it over. Hope this helps.

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