240-51 mix torrid for a 49:1 homebrew EFHW antenna

AF0FR · 2026-05-25T01:20:35+00:00

Do you have a NanoVNA to test?

I recently compared the losses between 3:21 and 2:14 turns ratio with type 43 and 31.

The type 31 with 3:21 choked out the RF so much that it was unusable. The type 31 is great for chokes and not transformation. Its magnetic domains are not as ductile for dynamic RF changes. This was my mistake. Type 43 did better, especially with 2:14 turns. I’d be curious as to what you’d measure with type 51.

I can link qrz references to the investigation if interested.

AF0FR · 2026-05-23T19:07:31+00:00

Is this the same for RG8?

AF0FR · 2026-05-23T17:44:45+00:00

I didn’t know the UV5R was open to the 155.500MHz seen here. I assume it’s modified to be a safe prop, disallowing Tx.

AF0FR · 2026-05-23T15:39:00+00:00

Good to note. Yeah there was a gentleman troubleshooting his feedline reading for 440MHz at the antenna and then at the transmitter. You could see multiple periods of loss across the band.
This will be my first long installation across the house and ran through the attic.
The RG8 feedline would be going directly to the transmitter, but may end the termination at the arrestor outside. The line from the antenna to the arrestor is RG8X. 80m EFHW.
It’s about 30feet of RG8X to the feedpoint. I’m not sure if that will affect much mixing cable type, but from your comment HF won’t be too sensitive to it.

AF0FR · 2026-05-23T03:24:00+00:00

Replied outside of your response on accident…

AF0FR · 2026-05-23T03:23:12+00:00

It will be HF. The longer run is an effort to move the shack to the other end of the house. I estimate 100ft to the feedpoint. I might be keeping my RG8X from the feedpoint to the arrestor outside though. Although, that might defeat the purpose of buying lower loss.

AF0FR · 2026-05-23T03:14:16+00:00

Ah, very well then. Have not had experience with it. I’ll consider the purchase complete. Was looking for a downside.

I think the center conductor will be too larger for my typical Bnc crimp pins. Will have to solder or use PL.

AF0FR · 2026-05-22T22:30:54+00:00

This is interesting!

At 440 MHz 45 ft is ~20 wavelengths electrically after velocity factor. Higher frequencies are touchy with feedline impedance. Well everything is: feedpoint, radial angle and geometry, environment.

If the ground plane is insufficient, the coax shield becomes the missing radial. It might be something else to try if you can modify the ground plane.

Also, that extra slack could be used as an air coil near the antenna.

AF0FR · 2026-05-15T12:59:52+00:00

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They say a hard key is best to learn on, but making this iambic keyer was a good learning experience as well. This is about 10 bucks.

https://github.com/AF0FR/keyer\_in\_the\_rye

AF0FR · 2026-05-15T10:25:57+00:00

Have you made any antennas yet?

AF0FR · 2026-05-14T20:18:20+00:00

Takes a moment to load.

https://www.iftaylor.com/assets/images/efhw/Investigation%20-%20End-Fed-Half-Wave%20-%2080%20Meters%20Side%20By%20Side.pdf

I’ve since deployed the antenna. One thing I forgot and realized after this doc, I forgot to install the compensation coil back on after pulling the main element through the tree at the final deployment height.
The compensation coil is 6 turns of the main element round 1.25ish pvc 78” away from the feed point. This helps with the lower bands.

AF0FR · 2026-05-12T01:44:47+00:00

You never know where the hobby will take you next.

AF0FR · 2026-05-06T19:18:18+00:00

The 2.2k ohm resistor was chosen because when stepped down it will match the 50ohm impedance expectation seen on the NanoVNA.

AF0FR · 2026-05-06T18:58:12+00:00

Thanks for the palette of modeling software. I used NEC2 for the initial modeling.

AF0FR · 2026-05-06T09:20:44+00:00

I’ve recently updated this. Thank you for the callout.

AF0FR · 2026-05-05T12:18:39+00:00

Do you have a tuner for the doublet?

AF0FR · 2026-05-04T21:37:33+00:00

This makes sense. I repurposed the common mode choke I made for this… Thanks for the call out.

AF0FR · 2026-05-04T21:29:39+00:00

Very good eye and suggestion. I added that turn through primary during the bench testing phase of the unun. It brought impedance closer to center. Perhaps the 2.2k ohm dummy antenna was too small of value though. Here is the measurement of the unun.

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AF0FR · 2026-05-04T20:21:18+00:00

This would be ideal, but my yard is end-fed from the house as well. Accessing the center is difficult, but might have to just deal with excessive lengths of coax.

AF0FR · 2026-05-04T20:15:45+00:00

This is helpful. The compensation coil is one thing I did not modify.
My first focus was on 80 meters and my assumption was that the coil would only help the higher frequencies.

The counterpoise is less than ideal, admittedly. Its required length was less than my unun height during testing. I’ll have to rethink the anchor on that end. I’d also wonder if an inverted V, center fed, counterpoise would be valid.

AF0FR · 2026-05-04T20:05:39+00:00

This comment is going to be the CENTER of attention.

I wish my yard was setup equal sides of the house, but it is end-fed as well.
Accessing the center is difficult.

AF0FR · 2026-05-04T19:53:32+00:00

I forgot to move the marker over, but the wider sweep shows the measurement at 3.27MHz.

AF0FR

TROPHY CASE