I get a fair amount of email about my earlier posts. Recently, a reader asked:
I was reading your post about end-fed, long-wire antennas, I think it was from 2016. I have a couple questions about end feds. Do you mind if I ask?
Feel free to ask, but I don’t claim to be an expert at all. My blog posts were just reports of some playing around that some of us did with end-feds.
So, he asked:
Thanks and I understand you are not an RF engineer or anything like that. This is my situation. I have a KX3 which I run exclusively 5 watts with CW. It has an internal antenna tuner. I have a 6 foot piece of RG58 that goes through a second story window and the center conductor connects directly to a wire about 135 foot long. At that same point the shield is connected to a wire that is about 35 foot long and it goes to a grounding rod. I don’t have any types of coils etc installed.
Depending on the RF gods, of course, this antenna can do an excellent job. For example I have a confirmed QSO to VK land, 5 watts via CW. Other times I hear nothing.
So this is what I am wondering. Am I missing something not using a unun? Is there an optimal length the wire should be for this situation? All bands except 80 tune up super. Eighty gets about 3.2 – 1. Leave well enough alone?
Any thoughts?
I replied again:
Personally, I don’t think you’re missing anything by not using an unun. All the unun does is bring the impedance down to a value where a lesser tuner can match the impedance to the transmitter. If your antenna tuner can do it without the unun—and the Elecraft tuners can really match just about anything—then why use an unun? It’s just adding some loss into the system.
As for as optimal lengths go, I think that the longer the wire you can string up the better—as long as you stay away from lengths that are exactly halfway multiples. Mike, AB3AP explains this pretty well. If you take a look at his figures (see below), it looks like 132 – 135 ft. is a length to stay away from.
That’s a half wavelength on 80, and I think that’s why you’re having trouble getting a decent SWR there. Try coiling up about 5 feet to make it shorter, or add 5 feet to the end and see how that works.