Gary, Your point about using bungee cords seems like a good idea. I've found some nice "GEAR Resistance Shock Cord Assemblies" on the Internet ( http://www.adrenalindreams.com/gallery14.html) that seem like suitable candidates.
I must admit that I can't quite picture the manner that you are using the tie wraps in your installation but it sounds like that arrangement is only suitable for a vertically oriented delta loop as opposed to my horizontally oriented loop. Rick On Sun, Sep 16, 2012 at 10:05 AM, gary bartlett <garybartl...@accesswave.ca>wrote: > I intended to post this here in case anyone else is playing with delta > loops. It's a lot of wire in the air! > > 73, > Gary VE1RGB > > -----Original Message----- > From: gary bartlett [mailto:garybartl...@accesswave.ca] > Sent: September 16, 2012 1:02 PM > To: 'Rick McClelland, AA5S' > Subject: RE: [Elecraft] Question about suspending a delta loop... > > Rick, I will describe what I have. Perhaps it will trigger something > useful > for you. > > I have a full-size 160M delta loop that is made from a single piece of > that > *Silky* jacketed wire which is wonderful around trees. It is routed over > pulleys at the three corners, with the apex at a yardarm about 90 feet up a > tower. The loop is roughly 75 feet per side, not a true delta shape. My > antenna is fed to the radio using ladderline and operated multi-band > through > a 9:1 Guanella balun from 160M to 6M. It's buried in the woods. It's > matched by the transmatch in my K3. I ignore the losses in the ladder line > with CW. > > It is ordinarily fed as a loop at one corner although I am experimenting > with what happens when one starts opening corners opposite to the feed > point > and feeding the antenna as some sort of irregular bipolar contraption. > From > the station I will soon be able to remotely reverse the feed points as well > as open or close relays at will at the corners opposite to the feeds. > EZNEC > suggests that I have a tonne of impressive lobes and low angles on some > bands. While the delta loop is off the best heading by virtue of > limitations on where I could hang it, I will at least be able to reverse > the > antenna patterns and see what that does for me. > > Up here we get freezing rain and high winds and ice build-up all at the > same > time, and is always a threat to wire antennas. Therefore I hang all my > antennas with bungee cords wherever the haul down ropes or other means of > securing the antenna are located. To this, at the most accessible point of > the antenna suspension system, I add a tie-wrap as the final means of > securing the bungee cord (and hence the antenna) at ground level. I call > this a frangible fuse, I termed I robbed from working in aerospace. > > > A physics guy can explain it better, but really big forces build up in the > antenna if it takes a sudden shock. Something about overcoming resting > inertia made sense to me when I read about it. Ballast is not a good idea > up here. We need something compliant like the bungee cords everywhere > there > is an opportunity to fit them. > > If the bungee cord goes to the limits of its travel, it breaks the > tie-wrap, allowing the antenna to gracefully sag to the ground and rest > until I pull it up again and replace the tie wrap. I want my antennas to > fall down without damage so I have built a deliberate failure point in the > system at minimum walking distance from the station. > > I have paid the price from having antennas destroyed by weather but this > method is nearly fool-proof and it has frequently been tested. No antennas > have been destroyed in this story. It doesn't matter what causes the > sudden force on either of my wire antennas; if it is bad enough, it results > in a graceful fall of the antenna wires to the trees below with its > feedline > intact and ready for quick return to service. > > 73, > Gary VE1RGB > > -----Original Message----- > From: elecraft-boun...@mailman.qth.net > [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Rick McClelland, > AA5S > Sent: September 15, 2012 11:38 PM > To: Elecraft Discussion List > Subject: [Elecraft] Question about suspending a delta loop... > > I have a 240' delta loop suspended at three points about my QTH. I've been > pondering adding another 47' but this is quite a challenge given the > dimensions of my suburban lot. One thing I'm considering is to make good > use of two trees located in a common area outside my property lines. Easily > said, but I would not want to hang a 5 kg line ballast at either of these > points because I can imagine a couple of neighbourhood youths scaling a > tree > with one of them cutting a line causing the 5kg weight to crash down upon > the tender skull of the other youth. > > Legal matters notwithstanding, my question is whether I'm inviting certain > mechanical failure if I fix the two endpoints outside my property lines and > make use of only a single 5 kg ballast on the tree located within my > property lines. The advantage of doing this is obvious, if any of the > supporting lines outside my property are cut, the antenna falls onto my > property and there is no possibility of injury to the perpetrators of the > dastardly deed. > > As a possibly relevant aside, I don't use a typical insulator at each of > the three suspension points. I use a 4" flat acrylic insulator with two 6" > acrylic insulators attached to the end of the 4" insulator such that the > resulting insulating apparatus appears to be a rather large 8" tuning rod. > In my non-mechanical-engineering mind, I imagine that having the insulator > arranged in such a fashion reduces the peak tension at each apex of the > triangle and also allows the wire to move more freely through the insulator > without binding at that point. I realize that this matter isn't related to > any Elecraft product but there are so many sage OMs here that I feel that > an answer will be quickly forthcoming and without controversy. > > -- > Rick McClelland, AA5S > Fort Collins, CO > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > -- Rick McClelland, AA5S Fort Collins, CO ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
