EARCHI End-Fed 40-6 build.

Back when I started Sota, i was looking for a quick and easy antenna for portable use, along the way other items have been built and obtained that have made this project not as critical.

The project is a simple 9:1 Unun that creates a match for a random bit of wire, it still needs an ATU, but makes connecting coax to a bit of wire easier!.

END FED 6–40 Meter Multiband HF Antenna

This project produces an inexpensive, multiband, end fed HF antenna matchbox that is quick and easy to setup and use. The end fed feature adds convenience, but does present another issue. The problem with an end fed half wave antenna is that the antenna presents a high impedance, creating a significant miss match with the usual transceiver impedance of 50 ohms. This miss match is significantly greater than typical tuners can accommodate without a matching transformer.

This project creates a trifilar wound, 9:1 UNUN (unbalance to unbalance) toroid matching transformer that will match the high input impedance of an end fed antenna into the range where most antenna tuners can produce good performance. The matchbox handles 100 watts of power. This project requires an antenna tuner to achieve satisfactory SWR.

The matchbox project uses readily available common hardware and materials. For your convenience, Emergency Amateur Radio Club of Honolulu volunteers make fully assembled matchboxes for those who don’t want to construct one. Proceeds support the club and amateur radio. Order information is included on the last page. 

Instructions for the simple build can be found at the EARCHI website HERE or you can buy the kit pre made from them also.

Preparing the Antenna Wire

Matchbox performance will be determined by two factors: The length of the antenna wire, and the capability of the tuner. The length of the wire should generally be between 22 and 60 feet for best performance. Longer wires may have excessive impedance for some tuners to properly match. Wires shorter may not radiate as effectively. A 30 foot insulated 18 gauge stranded wire antenna and connecting lug is included with the project and should meet most requirements. Experience has shown that most external tuners and many internal tuners will tune 80–6 meters with an antenna length of 22’ to 30’. If a longer antenna is desired, the provided antenna can be lengthened. Some tuners, in particular internal tuners, may not tune the full 80-6 meter range. You may need to try different wire lengths to optimize your antenna configuration. If you are having difficulty getting your rig to tune, start with a 26’ wire. This should produce good results on at least 40-6 meters using the narrowest performance range of internal tuners. Best performance is achieved with a coax of 16’ or longer. Additional counterpoise is not required in this design. The system works well in horizontal, sloper, and vertical configurations. 

I purchased the required bits and pieces and yesterday morning making it up, simply take your wire, and a Toroid T106-2 and wind it all together, solder on the lugs/connectors and pop it in a box! and while I haven’t yet used it in anger, I’m sure it will work a treat!.. Now to head out and give it a try! It may also become my default camper trailer simple antenna when touring as it will be the easiest way to get some wire in the air, especially now i have my elecraft T1 ATU!


2 thoughts on “EARCHI End-Fed 40-6 build.

  1. I’ve had good success with the K1POO OCF dipole. 40-20-15-10m, no tuner. As with all OCFs getting the overall length and feedpoint position (relative to each end) correct takes some tweaking but it only took me 15 mins to sort it out the first time with a Youkits FG-01 analyser. Also, if you don’t use the recommended current balun you are in for a bad time (common mode issues that is sometimes complained about, most likely they are using a voltage balun through ignorance).


  2. Pingback: Sota Activation – VK3/VS-036 One Tree Hill | VK3BQ

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