On Lord Howe Island last summer, on 160M, we deployed a Spiderbeam 18M fiberglass telescopic pole with a 1/4 wave wire taped to it. The excess wire came off the top like an inverted L and was tied to a convenient fence. There were two sets of 4 light synthetic rope guys to ground stakes. We had a bunch of radials made of electric fence wire on the ground and a small matching network at the base. Light, easy to erect, shippable, not too expensive and worked very well.
I believe we will have the same antenna on Campbell Island in November. No engineering required except for the matching network. Les W2LK On 7/30/2012 8:32 PM, bills stuff wrote: > The plan is to develop a simple, relatively inexpensive, relatively > light weight and shippable/airline transportable 160 antenna kit for one > man quick deployment for modest DXpeditions or contributed for use by > resident hams in rare-ish (for 160 m) locations.The ability to make > adjustments to actual deployments to provide matching is important since > such antennas are famously variable due to soil and local obstruction > environment and there should not be a need for antenna matching > hardware, especially at the planned higher powers. > > First cut electrical design:Inverted L using telescoping aluminum tubes, > two elevated radials and "hairpin" matching. > > Mechanical features of a prototype that was deployed: > > 9 Alum tubes 6', .058" walls, 2" diameter through 1" diameter -- this > gives a 50' or 15.3 m mast (it can be pulled upright by 1 person, or > probably telescoped up also) > > #14 wire ~ 28 m for top wire and 2X ~34 m radials (values after some > adjustment, not unique, some tradeoff between the top and radials) > > Base - 2 thicknesses of Walmart (cheap 8X11") ΒΌ" plastic cutting board > resting on ground with a ~ 1.5" wood cylinder bolted in the > center.SO-239 connector screwed to the board. > > Guys -- 4X 3/32" dacron rope attached at 7 tube height, angled at ~ 45deg > > Guys held down by sandbags (very effective and moveable) > > Inv L top wire end was at ~ 2.5 m height with a support of opportunity > (e.g., a tree) ~ 25 m from base > > Radials have their closest support near the base from plastic rings > looped through each of an opposite pair of the guys at ~ 6 m high and 6 > m from the mast.The radials therefore go from the base to the rings at > about a 45 degree angle.(Elevating the base and everything else, by a > meter did not seem to affect the impedance.Beyond that, supports of > opportunity were used - above neck height is always nice. > > This produces, with some fiddling with wire lengths, an impedance around > 20 -- j20 which can be matched using a practical "hairpin" coil shunt of > inductive reactance ~ 45 ohms ( 4 microHenrys, say 5 turns 4" dia). > > More details of the test case including the EZNEC example are shown on > my website.There are obviously a number of ways this design could be > modified/improved, several discussed on the website.However, the > tradeoffs with size, weight and complexity must be considered in the > light of the mission here which includes transportability and ease of > deployment. > > I am looking for collaborators to contribute ideas to help improve, and > potentially, test design issues.Check out the website at > http://n6mw.ehpes.com <http://n6mw.ehpes.com/> for the Itinerant 160 m > antenna project expanded discussion toward the bottom. > > The immediate target is designing and assembling a respectable 160 m > antenna that might go to KH8 on a DXpedition. > > Bill, N6MW > > billsstuff(at)gotsky.com > > _______________________________________________ > UR RST IS ... ... ..9 QSB QSB - hw? BK > > _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
