When I first started activating SOTA peaks with my 5W ATS-3B radio, I wanted to have the best signals possible, so I carried about 40 feet of 450-ohm window line and a very small telescoping fishing rod, with a small spinning reel. I cast a pilot line over a tree, then I brought up a larger line, and finally the antenna - usually a 40-meter half-wave dipole fed with the window line and a BLT-style tuner.
I already had experience with QRP gear in the mountains, and I had solid SOTA activations right from the start. The BLT tuner tuned the 40M dipole on 40, 30, 20, 17, and 15M, with excellent results. The flat window line rolled up into a neat coil, and it isn’t especially heavy, so I might have continued doing SOTA that way for a long time.
Since there are no trees above about 12,000 feet elevation here in Colorado, I used a Black Widow pole, almost 20 feet high, to support a 20M dipole, which I fed with a twisted pair of teflon wire. This antenna performed well on 20M, but it was obviously lossy on 40, 30, and 15M. The pole wasn’t rigid enough to support the window line, or 300-ohm line, so I never tried those with the pole. A 40M dipole seemed equally impractical. I certainly didn’t want to use a larger pole up there!
I knew that Fred KT5X and some other leading SOTA activators were using light poles with thin end-fed wires, and I traded emails with Fred - we discussed his methods. I wasn’t sure that an end-fed antenna so close to ground would radiate as well as a center-fed dipole. My Eznec models told me that the dipole had a better pattern. The turning point came quickly on a local summit above 12,000 feet.
I put up the 20M dipole using the Black Widow pole, on the rocky, exposed summit, in a huge field of sharp, loose talus. With a dipole you have three wires to manage:
One leg of the dipole
The second leg of the dipole
You also have to support the pole, somehow, in the talus, as there is nothing like a tree to help out. If it’s windy, the pole may not behave or even stay up, unless you guy it to the rocks. This means you may have to manage 2 or 3 guy lines, in addition to the three wires hanging from the pole. Everything wants to tangle, or to move to the wrong place!
The talus kept catching my wires as I struggled to lay them out in the breeze - I realized how hard this would be in a stronger wind - the kind that we often have above tree-line! Trying to balance, not fall, and function in the loose talus and thin, breezy air wasn’t easy, despite my years of experience in the mountains. Eventually I solved the puzzle and got on the air, and I had a nice activation, at least on 20M - but the feedline mismatch was too great on other bands, and I only made a few contacts once I quit 20M.
Earlier that year I had taken a QRP radio out in the woods, just to see if I could make any contacts with an end-fed antenna and a BLT tuner. There was a foot of melting snow, so I used snowshoes to hike into the saturated forest near my home. After casting a line about 40 feet up in a pine tree, I raised the end of a 65-foot wire, and then I tied it off to a stump at the lower end. The wire ran diagonally up toward the top of the tree. It was a half-wave on 40M, and a full wave on 20M. I got on the air, called CQ, and made a couple of rag-chew contacts on 40M and 20M.
I was impressed with the simplicity of the “system”. I got the big wire up high, despite deep, slushy snow everywhere; I made easy, conversational CW contacts on 20 and 40M CW, with just 5W. What really nailed it was that one of the operators sent me an email with a digital file - a recording of our contact. I couldn’t believe it - it sounded just like a contact from another home station - except I was sitting out in the woods in a foot of wet snow! My signal was fine - solid and Q5.
My end-fed experiment, done before I ever started SOTA, stayed in my head. After I was up at 12,000+ feet struggling with the wires and lines in the windy talus, I thought about how I could have set up using an end-fed wire. One wire would be so much better than three, all trying to get tangled in the wind. The pole would stand higher, and the one wire could serve as one of the guys - it was so logical. The same wire would go down the pole to my tuner, and I could even sit next to the pole to help steady it. There would be no feedline to unroll and connect. Much more important was that I knew I could tune the wire on any of the popular HF bands, and there would be no feedline loss, as with a mismatched dipole.
I did many experiments, mostly using different lengths of wire, some with counterpoises, and some without; I always activated on multiple bands. The one thing that needed improvement was the BLT tuner - it was struggling to match the roughly 3000-ohm impedance of the end-fed. I made a little high-Z tuner to connect between the BLT and the high-Z wire. It stepped up the impedance and allowed the BLT to share the matching at a lower impedance, where it was more efficient, from band to band. The two-stage approach was effective and easy to use, but it wasn’t ideal. After a couple of years of two-stage matching, I devised a single multi-band tuner to match high and low-Z antennas, to do the whole job, with fewer parts. It was simpler and easier than anything that I’d used previously, and I’m still using it. I just wrote it up on another thread on this website! It’s the “KX0R Tuner”.
A single end-fed wire is more practical and effective to use for SOTA activations than anything else we know about.
You can use your limited time on a summit any way you choose, but many of us prefer being on the air and making lots of contacts over struggling with complex antennas, feedlines, and heavy poles.
An end-fed system is safer than a traditional dipole, because it can be erected and taken down much faster. In windy, cold, or stormy weather, the advantages become incredibly clear!
Reducing weight and complexity buys you time and energy, especially at high altitude, when you don’t have enough of either.