How to build a proper Skyloop (Delta loop construction)
Well folks, I’ve been continuing my experiments with my two sky loops (closed loops of wire held above the ground at three or more points) and comparing them against various verticals. Sometimes the verticals win, other times the loops do. I’ve had 8m verticals and longer too. Today, I’ve put the 12m vertical back up (http://www.m0mcx.co.uk/?p=102) fed with my trusty SG230 coupler. I may add that anyone interested in fast antenna experiments should get one of these. A tremendous piece of kit. Matches anything.
Apart from the noise factor (loops are quiet), the vertical seems to make a better impact on transmit more often than not for DX, unless I’m into NVIS or near NVIS (500 miles or so). Even then, up to 1,500 miles, the jury is out - either antenna can win. Beyond 1,500 miles the vertical seems to do a better job most of the time - not always, however my loops are very low to the ground, maximum height of 7 meters. On 40m, I would say the vertical is a better antenna to have almost all of the time unless you need NVIS for local copying - and with the sun spot cycle as it is, you won’t get this for a while yet!
I used to have the opinion that loops were more often than not, cloud warmers. However let’s face it, so are almost all low-to-the-ground HF antennas. My interest was tickled recently when VE7HA mailed me an MMANA file of a very high (80- foot) 300 foot circumference skyloop that he had built with three very large trees. He claimed great contest results with this loop. I had a look at the plots. Yes, he was right.. Check this out, 10.4 dbi gain at 5 degrees to the horizon on 10m? On 15m band, we’re looking at 12.5 dbi at 7 degrees to horizon! On 20, it’s as good with 10.5 dbi gain at less than 10 degrees.
Now.. This is a very different animal to the Skyloops that most people build. If you want a pile-up generator, this is the animal to have. It fundamentally, takes all your RF energy and pancakes it low to the ground in various star shapes. Very Of course, you will sometimes null out the station you want but you could get really clever and change feedpoints with relays. But ignoring the clever engineering, this has changed my mind as to the effectiveness of a high skyloop.
Be prepared to get into some matching territory though, ideally an automatic coupler at the fedpoint with open wire feeder, or perhaps an olde-fashioned tuner in the shack!
Some day I will build one, I just don’t have the trees :(
73
Callum.
Callum,
I wish that we had been in a different part of the solar cycle when I had my loop up. I was never able to try it much on the highest bands since there is little activity there right now. The antenna did tune well on those bands using a manually tuned Drake MN-2000 tuner. The loop is down now in anticipation of putting up a Steppir yagi. However, I can put the loop back up quite easily using my homemade slingshot to create the anchor points in the trees if the Steppir plan drags. But there isn’t any 180-degree mode on a loop; that spoils you once you’ve had that feature.
Murray VE7HA / 7J1AQH
Comment by Murray | May 3, 2008
Hello Murray, thanks for visiting again. James (M3YOM) and I did some more analysis and it appears that 60 degree triangles produce the best far-field plots - better than squares - I believe there’s some interaction going on here as one would find in a rhombic.
Anyhow, we have an opportunity to build one with 30 meter (100 feet) legs, at around 60 feet above ground at the Scout Hut which we’ll try and get up this summer but it’s so dense in the forest that I wonder how on earth it’ll get up in the air. MMANA suggests that it won’t be too bad with even some decent gain on 40m.
Like you, we aim to tune this with an ATU inside the building, using 450 ohm feeder.
Cheers and beers.
Callum.
Comment by callum | May 3, 2008