PROJECT EFHW ANTENNA

In October and November 2024, we're going to build our own End Fed Half Wave Antennas, and wind a 49:1 transformer.

In September, Patrick K6PFG, gave a short presentation and encouraged each of us to build things that work well, and had high praise for the 49:1 antenna kit. We sourced the materials and gathered in October for a build session, spending our entire club meeting time twisting wire.

Congratulations to Vance for finishing his kit first, taking the un-tuned wire antenna outside and making a contact on 40m to Fallbrook and somewhere in Arizona. We'll be doing round 2 of this build process in November as several members were unable to attend. This kit takes a little bit of skill and patience, and we need another couple hours to really do it right.

I noticed a very cool thing in the photos. Vance decided to take a more technical route with his transformer build, and tapped the 2nd winding like an autotransformer. He didn't invent this method, but copied a style easily found for the 49:1 builds. Doing this requires a lot of attention to detail but when done, it proved to be very successful. I'm not sure this method will save you any build time since all the work must be done within the enclosure and needs a very hot soldering iron. Thanks for taking the path less traveled and showing it can be done!

Follow up - October 11 - Jon KK6VLO

I spent some time studying the HFKits documentation and reflecting on the design and deployment challenges the group experienced during our meeting. Bending 16g wire in a tight box is tough, and then trying to deal with the enamel coating in that same space is even tougher, so here is a description of the route I took. I used a PineCil64 soldering iron set to 690F using the largest tip I had (it looks like an animal hoof) and I used solder flux for doing copper pipe work. It seems to help get the solder to stick to these larger gauge wires like it does a piece of copper pipe.

The directions are from an original source, and describe the build operations for 250w. We're fairly closely following this guide. Scroll down to the image of the toroid and wire wrapped and twisted to see what we're doing.

https://www.hfkits.com/build-instruction-impedance-transformer-250w-for-end-fed-antennas/

I took the two segments of wire given at our meeting, and Ray helped make a very even twist about 5" long, about 7 to 10 twists is what we think is best here.
The short one is 9" and the long one is 34". This will give you plenty of wire manipulate and trim the trailing ends.

Following the images in the HFKits link, I wrapped the primary two windings so it looks like the example. We intentionally clipped the two wire segments before handing them out because one of the first steps after doing the twist is to separate them by cutting the loop.

After the primary two windings were done, I continued with the remaining turns on the lower half of the toroid, then the pass-thru and wound the top half. I pulled each of the wire ends to where they will connect inside the box. The long leg at the top goes to the top left of the box, and attaches to the 66 foot long wire. The three at the bottom attach to the center pin, the 259 shell, and the counterpoise lug. The 100pf cap goes between the pin and the 259 shell. When twisted and wound, you should have contuinuity between them as shown. The red and purple arrows point to the ends of each wire you just wrapped and you can verify this with an ohm meter.

Front, the way we're going to install.

Flipped over

I put the ring terminals inside the box and made them finger tight. I carefully bent and trimmed three of the legs so they will easily fit into the ring terminals, skipping the center pin for now. Better to leave them a tiny bit long as you do a test fit. Wire stretchers for 16g wire are very rare. This dry fit gives me a visual of how each ring terminal is going to fit on the fasteners, and what kind of shape the wire will take as it leaves the toroid. Once you have the desired shape of each wire, carefully remove all the ring terminals so we can solder them outside the box.

The dremel with a small sanding drum works best, and I removed the enamel all the way around the wire. Be sure to remove enough enamel at the twisted junction and each end, for maximum solder bond. I dabbed the twist junction with flux and went for it. It took a little time for a blob of solder to fully envelop the twisted junction and doing this outside the box lets me see the front and back more easily. The solder blob was bonding and falling away from my view, so I flipped it over and let gravity help until it appeared to completely surround the wires. Remembering how the ring terminals were oriented in the dry fit, I soldered them onto the wire ends at the same position.

Installing the terminals back into the box is easy. The M5 bolts drop right through and a few turns with some wrenches tightens them against the plastic box. Once they were tight, I measure twice and cut the wire to the center pin, then removed the enamel. We're ready to solder the center pin AND the capacitor.

Using a 3rd hand or some locking tweezers, I added flux and put a cap leg AND the wire into the 259 cup.
Take your time here and get everything into position.
We need to apply a lot of heat to this cup and only want to do it once.

Take your time and position the cap carefully.

With the center pin secure, gently bend the cap leg to the shell ring terminal. When I tried to make this bond, a solder blob easily formed away from me following gravity. To get the blob more onto the leg of the cap, I rotated the box so the cap was pointing down, then applied heat. That solder blob very nicely wrapped around the leg of the cap.

Adding the zip ties seems to work fairly well in this orientation.

You will need needle pliers to pull the tabs and don't worry about trimming the flap.

Pull the zip ties gently. They add stability to the toroid which is supported by the soldered wires.

Eye bolt and wire rope clamp

Use reasonably short loops at the eye bolt. This is part of your 66 feet.

M5 bolt assembly inside

This is the order of assembly suggested for connecting the enamel wire to the external wire. Tighten the ring terminal between the bolt and nut for a solid RF connection.

M5 bolt assembly outside

This is the order of assembly suggested for the outside. Tighten the M5 nut against the star washers to prevent rotation when installing your external antenna wire. The flat washer and wing nut have large surfaces for connecting the long wire ring terminal. If you want this box to be more weatherproof, add sealant around the base of these top bolts.

80m Coil Option

Here are some helpful hints for finishing your antenna based on content sourced from HFKits and other builders.

The PVC pipe and enamel wire need to be installed once your toroid is complete. The documentation instructs builders to cut the long wire at 66 feet, add the coil, add another 8 to 10 feet of wire, then begin tuning. Drill two holes at each end just big enough to accept the 14g wire. These holes will carry all the tension of the long wire and must not allow the 14g wire to slip.

How strong is that coil?

I wanted to see how much weight this coil could take, so lets try something. Using two cinder blocks, the PVC pipe segment is clearly strong enough to support the load, but the THHN wire has some issues.
The blocks are between 25 and 30 pounds each.

failure...

Using only the bent wire through our holes, the copper and jacket began to slide and tear when loaded with 50 pounds of force. Your temporary install of an EFHW antenna may never see this kind of force, but a permanent install could experience this many times. Intermittent tension on this coil over time could cause a failure. Consider this now before you deploy.

A Solution

Here is an easy option for securing your wire inside the PVC. Tie a half hitch knot in the short segment of wire used for joining the enamel to the THHN. This prevents the jacket and strands from separating under tension and prevents the wire from slipping through the two holes in the PVC. The knot method is described in the HFKits documentation as well as other build tutorials. Do this on each end of your coil connection.

If you have photos and a method to share, please contact president@wa6bgs.us

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