A while back I was looking for small and compact antennas, and I accidentally stumbled across this strange, mysterious looking antenna called the “Isotron antenna”. It’s so suspiciously looking, I have to quote my good friend Kristoffer, LBØVG, who said that “it looks like someone tried to make an antenna”. Not like the slinky-beam-tophat-beam-whatever antenna from Stranger Things, but almost there.

Isotron antennas are monobanders with a ridiculous small size: the 20m is just 53cm long. My gut instinct was that it would have extremely narrow bandwidth, but looking at the 20m version sold at the Bilal Company website, it’s claimed to be 350kHz covering the entire 20m band.

I could buy one, but don’t have the patience nor the attention span to wait for it to arrive. So I decided to build one myself, and here’s how it went:

I started by searching the web for instructions or plans on how to build one, but couldn’t find much to work with. Instead, I downloaded a picture of one, did some measurements, and took it from there. Here’s the original photo:

By measuring the size of the SO239 in pixels, I figured out the diameter of the top rod. Long story short, our broom is now 50cm shorter. As for the coil, I counted 20 turns, did some more pixel estimations and landed on 94 turns in total.

I had some spare copper pipe from a DIY car brake kit, and the metal plates was some scrap metal I had laying around. With some zip ties, electrical tape and a stub of PVC pipe for support, I ended up with this abomination:

I know it ain’t pretty, but again, this is just an experiment to see if there’s anything to it.

I hooked it up to my NanoVNA analyzator, and to my surprise it works on first try! Not perfectly tuned, but darn close:

The antenna is tuned my adjusting the distance between the top and bottom rods, so it was only a matter of mounting it outside and tuning while keeping an eye on the analyzer.

I know you’re thinking, “a dummy load also has great SWR!”

However, I did a quick test last night and – to be honest – it works better than a dummy load. The antenna is mounted on a 2 meter tall aluminium pipe (not grounded), total height is approximately 2.5 meters above ground. Not ideal, but again, I’m still at the experimental stage here.

The antenna is currently facing east, and I took it easy running only 5 watts from the radio.

I was delighted to have the first QSO on this antenna on 20m FT4 mode with ON4PS, with a distance of 1450 km. Not half bad sitting 2.5m above ground, 5 watts, on a first-try homemade Isotron.

The next part is to mount this much higher up, in one of the trees behind my house, and facing south.

Stay tuned for the next update.