I read about it here:http://www.rsgbshop.org/acatalog/PDF/StealthAntennas_Sample.pdf
K3MT’S GRASSWIRE ANTENNA
When I first read Mike Toia’s, K3MT, piece on the Grasswire antenna I checked the calendar to see if it was an April fool joke – it wasn’t! I’ll let him take up the story. Mike says: “This antenna will not out-perform a Yagi, or a decent dipole up a half wavelength. Not in gain or signal strength, at least. But it will survive an ice storm, wind storm, and is practically immune to lightning. And it doesn’t need a large tower or tall support. I deploy one from my hip pocket at times - the balun to match it is larger than the antenna!
“Put simply, it is an end-fed, long-wire antenna that is laid right on the grass, hence the name. The original Grasswire used by me in the summer of 1988 was just 204ft of #18 AWG magnet wire laid along the property line, anywhere from 1in to 6in above the ground. Either a ground rod or optional
counterpoise wires are also needed - use one or the other as both are not needed.” See Fig 8.2.
These antennas are largely resistive, with values ranging from 150 to 500Ω or so on average ground. They have been used successfully on all sorts of soil. One was used with great success by K3MT/VP9 in Southampton, Bermuda - the object of nightly pile- ups on 30m CW for four nights.
Mike says that the sceptic in you will doubt that such low antennas can work. After all, its image in the ground radiates and cancels out all radiation. True - if the ground is perfect. But nothing is perfect! The Grasswire radiates vertically-polarised signals off the end of the wire. Extensive monitoring tests have demonstrated the end-fire nature of the antenna. Mike says that launching a ray at, say, 15 - 20° take-off angle can be useful and that’s what his Grasswire does. It is lossy in all directions, but least lossy when exciting the ionosphere for a long-haul DX contact. He says that signal reports are not fantastic, but contacts are made and ham radio is enjoyed! And the best part of this set-up is that his neighbours never knew that a ham station was on the air.
Mike feeds the antenna through a simple trifilar unun (an unbalanced to unbalanced impedance transformer), choosing the connections he wants for 2.5:1, 4:1 or 9:1 ratios (see Fig 8.3). It is basically a wide-band, three-winding autotransformer. Impedance ratios are as shown on the drawing. Generally it is necessary to connect the coax to
Fig 8.2: An antenna that literally lies on the ground? Mike, K3MT, says that it does radiate.
either A2/B1 or B2/C1, and the antenna to B2/C1 or to C2. This may change from one band to another, and usually does.
Mike has also experimented with laying a Windom antenna on the ground. He says that it also becomes directional in the direction of the longest end. In both of these examples you will need to use an ATU.
Thus I thought I'd put my 80' horizontal loop "at grass level" by "erecting" it on some "painter poles" just a foot off the ground with some "Caution" signs around it so that (hopefully!) nobody stumbles over it. Would give me the flexibility to not have to depend on a tree and be able to move to the side of everyone else. Don't know how well it will work, but the "Grasswire antenna" described on the 'net gave me the idea.
vy 73 de Marcus KD0JKM