Yes, I made an End Fed Half Wave antenna. For a few years I've had a 31' tall telescoping fiberglass pole assembly made by a long defunct business called S9. I fabricated one of the 49:1 transformers, installed radials, and added a choke in the feed line somewhere near the ground. The location of the feedpoint and transformer are about 10' above ground. If I remember correct, the antenna has low vswr on 20, 15 and somewhat on 10 meters. No tuner needed, almost I think...

Because the height of the antenna is already a 1/4 wave on 40 meters, is there a good method for remotely bypassing this transformer so I can also use it on 40 meters? Could a relay be installed inside the transformer box to bypass it?

Thanks

A relay could work, but I would put it in a different enclosure than the EFHW transformer.

This video has a write up about doing the same idea with an 80M EFHW in order to use the element as a quarter wave for 160M.

https://www.youtube.com/watch?v=Ree8NtpEEW4

You could get a high voltage relay and use a pair of bias tees to open and close it. That's how I'm going to wire my dad's 80m cook on his 43' vertical.

Thanks to all of you for your input. I only used this antenna once last summer in thick trees on the West side of Mt. Rainier. I have little to compare the performance to, but during the two hours I tuned the radials and played with it, I was impressed. Adding 40 meters will make it worth the effort to install at home, though I feel I should raise the feedpoint yet a little higher and believe the radial lengths will now become much more finicky. I'm curious how the long term performance results will compare against something like a shorter height, dedicated 1/4 wave 20 meter vertical. If I can ultimately obtain good performance on 40, 20 and 15 meters, I will be happy.

My transformer is built on a single 2.4" toroid and is in a typical 4"x4"x2" gray junction box. It also has the little high voltage capacitor inside. There is no additional space inside, so a relay would have to reside in a second box. I'm thinking a Bosch relay is likely a poor choice for 100 watts. Likely something open frame with a 12 V coil.

I would like to be able to start listening to the ARFCOM digital net someday.

Feed your half wave antenna in the MIDDLE, no transformer required.

I just picked up several generic 12 volt automotive 40 amp relays and several switches.

I plan on installing them on the multiple taps of a wolfriver coil in the bed of my truck to see if I can change bands connecting the different taps on the coil to the antenna.

I think it will work, but not 100% sure, but at 100 watts mobile I think it will.

I found plenty of people online saying they used generic automotive coils in antennas at low impedance connections on antennas.

I will let you know if it works or not.

If you look in an auto tuner the relays aren't huge. A lot depends on where the relay is located, at a high voltage node you'll likely need an open frame (or vacuum) relay. I've heard from a club member that automotive relays didn't work on his wolf river coil. Let us know if it does. I want to make another mobile HF antenna and use a multi tapped coil and not a screwdriver. I dont use the infinite variability it offers.

what did he say was the problem, did the ones not closed arc?

I don't think there will be high voltages that is why there is a taps on the coil, but I might be wrong