^photo from manufacturer's website^I live in condo unit and most of my antennas are stealth affairs hidden behing the fences of my 2 patios, in the attic, strung along the roof edge and alike. By no means they work as good as the full size antennas of a similar disign, but they do work. For one, my fixed 17m wire moxon in the attic still surprises me every time I use it.
In the past I used the DIY small transmitting loop for 17-40m I build using old Russian vacuum capacitor and copper grounding strap from Georgia Copper. I made some SSB contacts on that antenna, but disassembled it as it wasn't robust enough of a setup/structure for me to use on a daily basis, just a proof of concept. At the time I had no antenna analyzer and it was pain to tune. But I liked the results, I remember reaching across the pond to Ireland on 20m SSB with ease, so I always wanted to finish the project.
Fast forward to October 2020, I saw >this< STL antenna on Internet. It looked ok, the description sounded even better, and I ordered it.
This weekend I assembled and tested the antenna, at first from inside the house at the 2nd floor as there was a tropical storm here in Miami for 2 days, and then, when the weather cleared, repeated tests outside, at ground level, next to the house.For testing, I decided to use FT8 as this is very sensitive mode and one can see instantly how the signal propagates/heard around the globe.
If you never used a small transmitting loop antenna, you should know that it is not the easiest antenna to tune. SWR plot's minimum could be very sharp and the antenna has to be tuned precisely to the frequency where it needed to be, otherwise the signal will not be best, even if the tuner is able to match the load to radio's output. The advantage of this particular loop antenna in its big butterfly-type capacitor with large dial, which helps fine tune the capacitance (that is how you tune the antenna). I used my antenna analyzer to help tune the antenna:
^17m SWR plot, inside placement^
^17m SWR plot, outside placement^
In house, the loop worked, but it was clearly compromized/attenuated/strongly influenced by the metal cage of the house and the objects in the room. This was obvious as I could not bring SWR down to less than 2 units before using the tuner, and by the signal reports I received (see below signal report maps). Nevetheless, I made 23 contacts, 4 DX (Azores, Mexico, Switzerland and Germany) and the rest was stateside. I started from using the antenna on low power setting but then, looking at the signal reports, brought it up to 90W and left it there for the duration of the test.The loop handled this level of power with no issues.
Here is the screenshot taken shortly after the QSO with CU6NS in Azores on 17m (antenna is inside the house!):
^^WSJT interface window top left with waterfall on top, JTAlert at bottom left, Flex radio interface (SmartSDR) in the center, interfaces to KAT 500 tuner and Elecraft SWR meter on the right. Click image for the original.
I compared the working of the antenna when it was placed outside with my other antennas, both hidden:
- bent 10m-40m doublet strung under the eves of the house at 20ft/6m high: the Magloop was much more sensitive on receive and at least as good or better on transmit
- attic wire moxon for 17m: moxon was better in its favorable directions, in all other directions the loop was on par or better.
To install the loop ouside, I had to weather protect it:
Here is couple of maps from https://pskreporter.info/pskmap.html site taken during the test on 20m and 40m.
Here is the map of some of the contacts made using the antenna:
Most if not all of the stations reporting good SNR were using beam antennas, but that's expected. There is no miracle here, just the quality made, robust small transmitting loop. I am happy to play with it and can recommend it to anyone who is interested in portable HF antennas.
73
