How Not To Build an EFHW

- 6 mins read

(…and have it work anyways)

Why a 40m End-Fed Half-Wave?

Convenience of installation; that’s it, that’s why I chose it. I can put the matching unit near the window of my shack, close to my grounding and lightning protection, using very little feed line, and just run a small wire into a nearby tree. The ~20m of wire even fits rather conveniently in my yard if I allow for some “compromises”. There are dozens of other choices that might work better, but I’m a new ham and I just wanted to put a wire in the air and have some fun. The facts that it’s cheap and simple to build are also pretty great.

Transformer and matching unit

The 49:1 impedance matching transformer was wound by my friend Andre (VA3HTP). We used 18AWG magnet wire, and it proved stiffer than expected, making the winding process quite a chore (especially after having to re-wind it due to a miscalculation on length). The core is a mix 43 ferrite (16.76mm OD x 39.12mm ID x 22.23mm L - Fair-Rite Part #2643251002). As you can see, a beautiful looking transformer is not strictly necessary, the turns ratio is what matters most, and this all gets hidden in the box anyways.

EFHW matching unit

We used a black ABS box which fit everything pretty comfortably, but was a bit of a PITA to drill. I also didn’t have a large enough drill bit for the panel mount SO-239 connector, so just used the closest one I had and carved the rest of with a knife. The transformer is affixed to the back using a bit of Duct Seal, which felt more serviceable than hot glue.

The capacitor is a ceramic type 100PF (3KV). We used a machine screw, washer, and two nuts to connect the antenna wire via an eyelet connector.

Installation

The antenna wire itself is some cheap 18AWG speaker wire that was on sale at the hardware store (I peeled apart the two conductors and just used one).

Speaker Wire

The setup is a bit of a compromise since convenience of installation was my primary concern. The matching unit simply hangs by some twine from my pergola, 7ft or so off the ground, and the wire runs up into the tree, maybe 25ft up if I’m lucky, before coming back down with roughly a 90 degree bend back towards the corner of my yard. I slung it through some other trees and tied it off to a convenient branch about 4ft off the ground.

Are there ground losses? Oh yes. Is this so low that it’s considered NVIS? Maybe. Am I overly concerned? Definitely not.

You might ask about weather proofing (It will contend with Canadian winters, after all), and to that I say: let’s see how it goes.

Common mode choke

If you’re a seasoned ham, you might notice that there is no counterpoise, which means that the outer shell of my feed line is going to be the counterpoise instead. I’ve got 10ft of coax between the matching using and the lightning arrestor, which seems like plenty for a counterpoise, but it needs a common mode choke to prevent the RF making it back into my shack.

This is 13 turns of cheap RG-8X around a Mix 31 ferrite (35.56mm OD x 60.96mm IDx 12.7mm L - Fair-Rite Part #2631803802). It probably works.

Common Mode Choke

SWR, and Performance

So how does it tune up?

Even though it’s a “40m” half-wave, I tuned it looking at the 20m band on the analyzer while trimming the wire to make sure I was covering the wider band adequately.

20m SWR is between 1.25 and 1.55 across the band. Not bad!

40m also good; from 1.5 at the top of the band, to just above 2 down at the bottom. Perfectly usable with my 3:1 auto-tuner.

15m is actually the best yet! Barely squeaking above 1.5 at the bottom of the band.

Even 10m is usable, staying under an SWR of 3 all the way across the band.

While I don’t have VNA snapshots for them, I was also able to get it tuned up on 17m and 12m, making this antenna usable on 6 bands!

Does it radiate, though?

PSK Reporter

Yes, it certainly does.

First failure (May 23 2025)

Well it survived the winter! But while moving it around in the spring, the antenna wire came out of the eyelet connector. The insulation was clearly rotting and the stranded copper flaked away. No worries, I just cut a few millimetres off the end, crimped on a new eyelet, and hooked it back up. Gave the whole area a bit of dielectric grease treatment to stave off the rotting. That’s weather proofing, right?

Dialectric Grease

Second failure (Jun 14 2025)

Not long after the first failure, I suffered a second, again while moving things around. The internal connection between the magnet wire and the antenna connection post popped out.

Antenna connection popped out

I reattached the wire and tightened it up real good, noting just how clean and unperturbed things looked inside the box, despite the total lack of weather proofing.

I decided that it was time for some upgrades, so I added some twine and zip-tie based “strain relief”.

Strain Relief

At the other end, I installed this snazzy plastic insulator, and upgraded the branch-based auto-tensioner to a more sturdy looking branch.

Insulator tied to a branch

I’m betting it lasts all the way until next spring this time, but we’ll see what happens when I take it down to refinish the pergola.

Third and fourth failure (Aug 08 2025)

Well I’d have lost the bet about lasting until next spring. While refinishing the pergola, with the wire laying on the ground, an animal (I suspect a rabbit) bit right through it. I re-hung it, but it was down on the ground THE VERY NEXT DAY. (This time I suspect a squirrel)

At that point, I only had enough usable lengths of wire to build a 20m dipole

A few weeks later I found time to hang a fresh wire. I upgraded to 16ga speaker wire, and used a DIY Arborist’s Throw Bag to get it up over the highest point in the tree. It’s now much closer to a clean inverted-V, with the center likely twice as high as it used to be, and the unfed end much higher off the ground.

References

In case you want to build your own, better, EFHW, here are some of the references I found most useful: