Unfortunately, for love nor money, although I managed to assemble most of the bits, I couldn’t find the gamma match arrangement in all my Tesco boxes. I needed this because unfortunately the impedance of a three element yagi is well under 50 ohms so unless I went for just a two element beam, I would have to re-engineer things. I recall that a loop had a higher impedance, about 100 ohms. Using a closed loop system with a reflector and a director would bring the loop impedance down, probably by about half (according to the modelling) to achieve 50 ohms. I modelled it and things looked very promising. Wide bandwidth and pretty good gain.
I’ve been an addict of full wave (and partial wave) loops since realising many years ago that in comparison to a dipole, you get more bang for your buck if you build a loop – certainly you get more copper in the air – and loops are resonant on EVERY harmonic so a 40m loop will be resonant on 20, 15m and 10m. A multi-band antenna for peanuts. They will receive better too, so for a housing estate, these are mandatory.
When I first started out with this hobby, I had a half-sized G5RV and I genuinely thought that I’d never get onto the 80 meter band. Within 18 months, I had worked out that you can build a loop of a wavelength in circumference (give or take a percent or so) and feed it directly with coax (and a 4:1 balun). Even better was the idea of putting loading coils in each corner of a square loop and you could lower the resonant frequency by a substantial amount.
You may have a smallish back garden like me; 10m deep and 14m wide. Your 40m loop (that’s really 40m [or so] all the way around) will resonate on the 40, 20, 15 and 10m bands. Mine is only about 20 feet off the ground, around gutter height. Its not quite square but the far side and the near side are completely different lengths to make it nearly a triangle. Not quite. I have coax to the feedpoint and a cheap 4:1 balun there. With some trimming on a sunny day, you can make it work on all the amateuir bands – and I even used it on 2m once!
My 80m loop was (and still is) square at about 15m per side which is actually too small for the 80m band. My 80m loop is actually 60m all the way around. To make it “bigger”, I added 4 x loading coils into each corner. These coils are 2 inch in diameter, 6 inches long and approximately 30 turns on each coil. With some farting about, you can easily make it tune either the CW or the SSB portion of the band. If you have a tuner, you’ll dial that out easily anyway, particularly at lower power: 400 watts and under. The 80m loop happens to work on 30m band too. Just a fluke. Great for digital.
I’m currently writing an article outlining the characteristics of the Mega Loop antenna we use for Dorridge Scouts. If you would like a preview of this white-paper, please let me know.
The XXT Mega Loop is the name given for the application of a horizontally mounted delta-loop that has known gain dependant on wavelength size and height above ground.
At quarter wavelength above ground and above, Mega-Loops start exhibiting gain that is proportional to its wavelength and height. A whole series of articles is currently being written by the author, however for the time being, these few articles may help you determine how we operate the Mega-Loop at Dorridge Scout Group HQ.
Firing supports over trees:
The 160m Loop
Picture shows Aidan, M6TTT running his first pile-up from the Hut. First class Aidan, you really got the swing of this on Sunday. Fabulous effort.
We put nearly 800 QSOs (contacts) in the log and there are so many highlights, I can’t begin to mention them all. My personal highlight was working VK3FT at lunchtime today with a land-line quality copy on the 20 meter band. Keith spotted us which probably accounted for flurry of VK stations immediately afterwards from Australia. Thanks Keith.
We got spotted 25 times over the weekend which is certainly our personal record. Thanks to those stations that helped us maintain the pile up!
As usual, we used the MegaLoop (delta-loop) antenna, see this page for details: