Long time QRPer.com contributor and supporter, Jonathan (KM4CFT) has designed and started producing ultra-compact end-fed antenna kits (eBay affiliate link).
His end-fed antennas are incredibly small, thus perfect for portable operations. They remind me very much of K6ARK’s end-fed wire antenna kits, but a little easier to build because the board is larger and there are no surface mount components.
Jonathan sent me one of his end-fed kits (assembled) a couple weeks ago, but I’ve yet to trim mine due to my crazy schedule and activities as of late (well, that I need need to order more wire!). I will take this antenna to the field this month, but the video may not show up for a few weeks.
W2AEW Builds the KM4CFT UNUN
This morning, I learned that my good friend Alan (W2AEW) published a video where he builds, tunes and tests Jonathan’s QRP End Fed UNUN kit:
Click here to watch on Alan’s (excellent) YouTube channel.
Alan’s video is superb. If you purchase this EFHW kit, I’d encourage you to watch his build. (And subscribe to his channel!)
How to purchase
Jonathan is selling his antenna kits on eBay–click here to check it out. The price is $29.95 plus a modest shipping fee. I think it’s an excellent deal.
Of course, you’ll need some wire for your radiator and/or counterpoise.
I plan to build mine with a 30 meter link to pair with my Mountain Topper MTR-5B.
Click here to check out the antenna kit on eBay. (note: this is an eBay partnership link that supports QRPer.com)
Looks like an excellent kit. One point of order: that’s an autotransformer (AT), not an unun, as the eBay page says. They look similar, but the difference is significant, so it’s worthwhile to get the terminology straight.
Either way, this one is a great piece of equipment.
Actually – if you look at it carefully, it is not an Autotransformer. An AT has one winding with a tap to make the primary and secondary. A key feature of an AT is that one part of the winding serves as both the primary and secondary. In the case of this transformer, there are two windings that are connected at the “tap” (i.e. the tap isn’t an input or output), so you have independent primary and secondary windings.
Here’s an idea; wind a 49:1 and a 9:1 on the same board, with a DPDT slide switch to select either one, connect to the unit enough wire for (say) a 40m EFHW, but add a spade or similar connector to the end of wire (once tuned) the connector will allow to bring the lenght to a “good” one for a random; this way the antenna could be used as an EFHW on 40,20,15,10 and, just by adding wire and switching to 9:1 as a “random” on all other bands 😀
An interesting idea. I think it can be difficult managing all the stray capacitance when designing these switchable baluns. The other issue, is that the EFHW is often used by people without tuners, especially on portable qrp setups. The 9:1 will pretty much always require a tuner of some sort. Maybe add a very small L-match or something to the board?
I love it, it is really smaller than my EFHW. I use for 40-20-15-10 at home.-
I will try to find this kit and buiilt one just for portable.
Instead of 49:1 I use 64:1 and I added a second wire for 30 meters, 46 ft , sloping in another direction.
It works like a champ.-
Thanks for sharing , it is very much appreciated,
All the very best,
72 Mike VE2TH , The QRP’er for 60 years.-
Just found, very interesting, my 1st qrp was a Dx20 nearly 70 years ago, now back on it on cw with a one watter…
VE2QM
Great article and great concept of an antenna, unfortunately the seller sells to every other other country in the world apart from the UK at the moment.
Can this be edited to reflect this as i have already contacted the seller and states the eBay global shipping system apparently is having problems to the UK and that there are a large number amateurs in the UK contacting them about making a purchase but at this moment in time are unable to this has been ongoing since at least October.
Wonderful video as usual, Thomas…Was wondering when and where the 2024 W4 SOTA Camp Out will be this year…73’s, Randall, WB4BBF
Hi, Randall, I believe the fall campout will be in North GA again, but I’m not sure of the dates nor the venue. Likely one of the parks we used in 2022 and 2023. There’s a W4 SOTA email discussion you should join if interested! https://w4sota.groups.io/
Cheers,
Thomas