This is an interesting discussion about antennas for forest regions where you have very tall trees. I have a lot of trees, but getting an antenna to 45 or 50 feet would involve very small branches. I have mostly Chinese Tallow Trees with some Ash and Beech, so stringing a wire from trees is marginal for me. I do have a 65 foot tower and conductive soil, so the trombone elements from SteppIR work well for me. You will be surprised how directive a rotatable dipole at 65 feet can be for 30 and 40 with 6 to 10 dB nulls at the ends and not much loss over a full dipole. A 60 foot wire vertical from a ground stake to the top guy is a good 80 meter antenna and if you add an 80 meter trap and a drooping extension it pretty good for 160. I have lived near a neighbor with 100 foot pine trees and I have seen them leaning nearly 45 degrees in 100 mile an hour winds during Hurricane Alicia. I think a wire antenna would break. Willis 'Cookie' Cooke, TDXS DX Chairman K5EWJ & Trustee N5BPS, USS Cavalla, USS Stewart
On Thursday, June 26, 2014 12:57 AM, Jim Brown <j...@audiosystemsgroup.com> wrote: On 6/25/2014 5:43 PM, Dauer, Edward wrote: > So, I've been selecting two of the tallest > candidates a couple of hundred feet apart and stringing a stout nylon rope > between them. In the middle of the cord I attach the balun for the Vees, > thereby allowing the legs to be in the clear, moveable from side to side, > and tied to smaller (8') trees at their distal ends. In one variation on > the theme I had a 40 meter dipole as the center section of the supporting > rope, tied to the same balun as an 80 meter vee. In another I tried a > linear-loaded 80-meter Vee, about 45' on a leg; it loaded fine but didn't > perform as well as the full length version. If you can suspend a flat antenna between two tall trees, why would you want an inverted vee, which is a less effective radiator? Your two trees 200 ft apart could support a full size 80/40 fan and a 20/15/10 fan, in line with each other. A high 80/40 fan is a VERY good antenna, and is easy to build. My technique has evolved to starting with #8 bare copper from the big box store, stretch it VERY slowly between a tree and a trailer hitch until it breaks. Do this carefully where there's no one around to get hurt. Now you have #10 hard drawn copper, which is pretty strong, and pre-stretched. Use that for the longest dipole in each fan. Use #12 or #14 THHN (house wire) for the other elements. I make spacers by cutting 1/2-in PVC conduit into lengths of about 16 in for 3-wire fans, and about 12 inches for 2-wire fans. 5-6 ft between spacers is a good rule of thumb. Hold the spacers in place by soldering short lengths of copper around the spacer to the bare copper of the long element. The higher your antenna is, the more robust your center insulator should be. A high 80/40 dipole (80 ft or more) will be closer to 75 ohms than 50 ohms. A 20/15/10 fan will be close to 50 ohms. Use RG8 or RG11 depending on the Z at resonance. Don't waste a dB or two with small coax. My 110 ft 80/40 fans are fed with Belden 8213. For weights, I fill 6 gallon water jugs with dry sand, and tie one to one end of each span. The other end can be fixed. I have pulleys high my trees. If you don't have a pulley and weight, your antenna WILL end up on the ground, and it won't take a big storm for that to happen. My HF antennas are all at the 110-120 ft level in a dense redwood forest that towers 50-75 ft above them. They work. My "seat of the pants" observation is that attenuation increases with frequency, and is greatest with vertical polarization. 432 MHz is a waste of time, 2M sort of works, and 6M works pretty well. For an analysis of the value of height, study this. It supports the statement earlier in this thread that a high dipole beats a low tri-bander. http://k9yc.com/VertOrHorizontal-Slides.pdf When Fred observes that the ends of antennas are "hotter," he means that this is voltage maxima and a current minima, so good insulation is needed to whatever the antenna is attached. I once melted heavy dacron rope that was tied directly to the end of said dipole (well, twice, actually). The extra ingredient was that it was wet. Duh. 73, Jim K9YC ______________________________________________________________ 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 Message delivered to wrco...@yahoo.com ______________________________________________________________ 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 Message delivered to arch...@mail-archive.com
