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Posted: 1/14/2022 10:42:27 PM EDT
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
Link Posted: 1/14/2022 11:50:58 PM EDT
[#1]
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
Link Posted: 1/15/2022 7:10:59 AM EDT
[#2]
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.
Link Posted: 1/15/2022 12:19:33 PM EDT
[#3]
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.
Link Posted: 1/17/2022 12:46:21 AM EDT
[#4]
Feed your half wave antenna in the MIDDLE, no transformer required.
Link Posted: 1/17/2022 10:58:14 AM EDT
[#5]
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.

Link Posted: 1/17/2022 11:08:23 AM EDT
[#6]
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.
Link Posted: 1/17/2022 9:18:49 PM EDT
[#7]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
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.
View Quote


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
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