N3NWV has planned an antenna build party!

The WW3AAA club project for summer 2021 will be an antenna build!

Many of us have gotten the portable operation bug, so the antenna we’ve chosen to build is an end-fed wire; specifically, an ½ wave antenna for the 40M band. An end-fed half WAVE (EFHW) has several positive features:

- It is resonant on every harmonic, not just odd or even. An EFHW cut for 40M will resonate on 20M, 15M, and 10M as well – typically with wide enough bandwidth that no antenna tuner is needed in operation.

- It requires very little in the way of counterpoise. The design of the kit does include a connection point for a dedicated counterpoise wire, but typically your coax is all that is required. Even when using the coax as the counterpoise, common mode current is minimal, and you are unlikely to experience any “RF in the shack” problems.

- Only one point of elevation is needed. An EFHW is easy to deploy using most any fiberglass mast or your nearest tree.

We will be building two components: the radiating element and a 49:1 UNUN.

The radiating element is an ~67 foot piece of wire. Common copper-clad aluminum speaker wire is used to keep both the cost and weight of the wire to a minimum. Construction is simple:

- Cut the wire to length

- Attach a 1” piece of 14AWG solid copper wire to one end with solder and heat-shrink tubing. This serves as the point of attachment to the UNUN

- Fold over ~1 foot of wire at the far end and secure this section with heat-shrink tubing. This provides a loop for attachment to a rope or mast for deployment. The folded over section also helps the tuning on 15M.

The completed wire looks something like this:

The end of a ½ wave radiator is a very high impedance; 2500 ohms or so. To connect this to our 50-ohm coax and radio we will require an impedance transformer which most hams refer to as an UNUN (unbalanced-to-unbalanced). The circuit diagram for our UNUN looks like this (ignore the parts list – it’s for a seriously QRO version):

And the finished product looks a little like this when you’re done (mine has a BNC – the club kit has an SO-239. Also we’ll be adding a binding post for the GND connection as a “just in case”):

The whole thing is a very easy build. Don’t worry if you’re not the best at soldering. These are easy to access and not too sensitive to over-heating. Plus, there will be gurus on hand should you need an extra set of fingers. All the required parts come in the kit, and we’re planning a “build party” so that you don’t need to have any tools or experience to get it assembled. Date of the party is TBD but we’re targeting August so that we have a club event for every month while there are no meetings.

Kits are $20. You can wait to pay for it until you pick it up, either at the build party or if you can’t attend that then by arrangement to meet up with Matt-N3NWV somewhere. You just need to drop an email to N3NWV at mattheere@hotmail.com or contact him on the 146.85 repeater and let him know that you will want one of the kits.