Home brew 80M endfed antenna

[Nashua Area Radio Society]

Good afternoon. Going to try to make this antenna. I have a roll of 12ga, insulated wire (19mils), and a 9:1 UNUN. Wondering if 12ga. overkill and impact of insulation on length. Plans I have found call for 71’10.25″ of bare wire. Know there are adjustments for insulation, just not how much. Your counsel appreciated.

73
Tom Mahon
AB1NS

[Martin Blustine]

Hello Tom,

You have correctly chosen a non-resonant length to use with your 9:1 UNUN. Strictly speaking, #12 AWG exceeds the National Electrical Code for wire antennas shorter than 150 ft! What it says in 810.52 for transmitting antennas for wires shorter than 150 ft is that you may use #14 AWG. The wire may be either hard-drawn copper, copper-clad steel, bronze or other high-strength material.

The length that you specified should work without much correction in length. There would not be a large adjustment for velocity factor due to insulation. I would advise you to begin with a slightly longer antenna length. Try pruning it down a little bit to see if you can improve the match at your desired center frequency. Even so, you will probably find that there is still a significant mismatch that will require the auto-tuner in your rig or an external antenna tuner near your rig.

I am assuming that you chose the 71′-10.25″ length based upon available space. There is a nice table of non-resonant lengths at the Balun Design website at https://www.balundesigns.com/content/Wire%20Lengths%20for%204%20and%209-1%20ununs.pdf

Good luck with your antenna.

Marty Blustine, K1FQL

[Nashua Area Radio Society]

Marty,

Thanks for coming back to me. I chose the length based on a couple of articles I found on line and a small yard About 120′ long, but large trees on both ends. I have an LDG AT-200ProII tuner. Just trying to make sure I’m on the right track.

73
Tom
AB1NS

[Martin Blustine]

Tom,

You are definitely on the right track.

I would suggest that you read the Balun Designs reference, above, w.r.t. counterpoises, radials and grounding.

Two other good papers to read are ones written by W8JI at

https://www.w8ji.com/counterpoise_systems.htm

and

https://www.w8ji.com/fcp_folded_counterpoise_system.htm

If you would consider using an inverted-L configuration, you could lengthen the wire and it will still fit your property. Then, you can ground the UNUN to ground rod, or install radials, or install a counterpoise.

You may also want to install a common mode choke or two. They should be installed where the common mode currents are expected to be maximum on the coaxial line. Placing them at arbitrary positions on the line is of little benefit.

All that having been said, your antenna can be modeled in EZNEC which is now free to download and use. If you have never used EZNEC, I can try to help if you would like.

Have fun.

Marty, K1FQL

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