The SWR values on the NANO VNA looked great… and then I compared them with my endfed for 40/20/15/10m at the summit and was extremely disappointed! It was significantly worse!
Colleagues told me that RG 58 would have been the better choice… but that would have been too bulky for me.
I then turned to the topic of oblong. But that is usually too bulky for me on the way to the summits, especially because I often do several summits a day… so I mostly continue to use my endfed…
No, no ground mounting assumed. In reality, I don’t ground mount a vertical, unless that is the only option. It is usually much better to elevate the feedpoint a few meters above the ground, because the antenna/radial creates fields which react with the ground, and much of that will get lost.
An elevated vertical dipole and a 3/8 vertical monopole with decent radials would perform comparably. If you are only interested in one band only, either one would be equally fine.
Another advantage of a monopole is that, when you try to make a multiband antenna by switching out the matching network, it can perform in a wider range of frequency than a dipole. Let’s just use an example. 3/8 WL monopole for 10m band is 4.0m-long. This antenna would perform ok on 20m through 10m with a proper matching network (20/17 shorter than 1/4 but still an ok-range. 15m would be almost 1/4). A vertical dipole for 10m would be 5.3m-long. This would work ok on 10 and 12m. I haven’t simulated for this particular case but it’ll probably have a messed up radiation pattern on 6m.)
If you are looking for a better antenna, the next step up would be a half square, bobtail curtain, or phased array.
I don’t use a J antenna, but I use 1/2-wavelength vertical monopole. In short, the difference is that I use a transformer and matching network in place of the bottom portion of the J antenna. The current distribution and the radiation pattern are, theoretically, supposed to be the same. And my antenna works very well.
I’m a believer of good theoretical consideration in antenna design (and circult design as well). So, why would I use such a skeptical wording in the above paragraph? That is because I only believe if the theoretical model reasonably reflects the situation of how the antenna is actually deployed.
J antenna is notorious for being sensitive to the supporting mast and other environmental conditions. When people use J-pole on VHF, they usually mount it on a metal mast. But when using it on a summit, people often hang it from a tree branch. In the latter case, it helps to use at least one radial, even a short one, to make sure the antenna works well, The radial connects to the cut end of the bottom transformer section. It can be significantly shorter than 1/4 wavelength. You may re-adjust the feed point for optimal match after adding it.
There are reasons why major commercial antenna manufacturers do not offer J antenna. If you try to do this right, it’ll look a bit strange. If you make it look like a J pole, its performance becomes sensitive to how it is deployed. This is a marketing nightmare. (Good looking lousy performance antennas sell a lot better than ugly antennas that work well. I heard from a Japanese antenna manufacturer that sold a lot of lousy good looking ones.)
