As you’ve probably noticed, I enjoy tinkering with antennas… and I like oblongs.
I treated myself to a 14m Spiderbeam mast at HAM RADIO. The VK/ZL ↔ EU S2S Party is the perfect moment to put it to use…
The thing is quite heavy, and normally it should be guyed with ropes. However, doing that alone with this monster is difficult. So, I built a mount that allows me to strap it to fence posts, signposts… and other sturdy supports.
It’s not suitable for every summit, of course—but it should work on my local peak, DM/BW-018.
Just in time for the VK/ZL ↔ EU S2S Party, I quickly built an oblong antenna. If the NanoVNA is to be believed, it works on other bands, too…
We hung a 20m Oblong off the side of a fire lookout tower for the Scouts for JOTA last year.
One issue with using loops is that the average height is less than the top height, and a dipole often has more gain if they aren’t up high enough. Here is a plot of the relative radiation at a vertical angle of 10 degrees for various loop shapes as a function of the top height in wavelengths:
(This is for 10m, so the bottom scale can be read as tenths of wavelengths.) The blue line is a horizontal dipole, and the grey line is a 50 ohm oblong. Note that the top of the oblong be about 3/4 wavelengths in the air to equal the signal from the dipole (assuming flat ground). Whether that applies to your specific mounting location or not will depend on the details. It might be worthwhile comparing results between an inverted vee tied off the top of the mast, and the oblong at the height you are using it (granted that the inverted vee with a fairly flat angle will need to be tied off quite some distance from the mast, which might not be practical).
@S52FT - Bostjan - Of course — I had already shared that link in my thread about the 10m oblong. … DK7ZB’s site is fantastic!
Like so many others, I’ve often found inspiration there and have built several of his antenna designs. And naturally, it served as the basis for this antenna, too — even though I didn’t stick strictly to the dimensions he specified. I might be losing 0.1 dBd of gain, but it makes the antenna a bit more manageable—especially for SOTA!
@WB6BYU - Dale - That is absolutely interesting information… I wasn’t aware of that before.
I plan to position the antenna so that the terrain drops off sharply after about half a wavelength. I think that will help its performance.
That is generally something I take into account during my activations! I very often do multiple activations in a single day. In doing so, I consider the position of the sun along my hiking route and at the activation site itself… but also factors like achieving a good radiation pattern. I like using a steeply sloping mountainside facing (north)west when activating in the afternoon, hoping for a signal path toward the USA.
DM/BW-018 slopes down toward the west… that would work quite well for the long path toward VK.
