I'll second Stewart's recommendation whole-heartedly, Nicholas. I also have a very small garden and use a doublet fed with open wire line. The doublet is a total of 45 feet long overall, which works FB down through 40 meters (the effectiveness of a center fed wire doesn't drop appreciably until it gets almost to 1/4 wavelength overall - or about 33 feet on 40 meters).
I arranged a 25 foot support pole just outside my shack window to hold it up in the center. One end drops down to a support about 10 feet high and the other end runs almost horizontally across to a point at the peak of my roof. That combination works FB on 20 through 10 meters gaining me all the DX I can hear - and that's a great deal when the bands are open. That length makes the antenna an "extended double Zepp" on 10 meters, which is the longest antenna one can use on 10 meters without getting into high-angle radiation lobes. Of course, with the diminishing sunspot cycle 10 meters won't be such a big issue except for those 10 meter enthusiasts who watch for and enjoy the openings that occur all the way through the minimum. They're there. They're just a lot less frequent than in the recent past. As Stuart said, horizontal antennas are much more efficient than a vertical because they don't have the ground losses that verticals have. That isn't just losses due to a ground connection, but includes losses caused by induction of ground currents some distance from a vertical that don't occur with a horizontal. But to provide low angle radiation for DX operations with a horizontal antenna, you need to have it up close to 1/2 wavelength, at least, above the ground. Lower heights will give you great high-angle radiation for short-skip/local contacts out to perhaps 600 miles or so. That's what is often called a NVIS (near vertical incidence system) today. So, for good DX effectiveness on 40 meters you need to have your dipole up about 50 or 60 feet at least. For many ops, including myself in my present QTH, that's out of reach. In that case, for contacts out beyond 1000 mi., a vertical, with its inherent low angle radiation, can produce much better results in spite of the ground losses. What I do is to feed one half of my doublet - the half running almost 30 feet straight up the pole and then horizontally about 25 feet to the peak of my roof, as an end-fed "Inverted L" on 40 and 80 meters. A 1/4 wave counterpoise wire makes a good RF ground to load the "L" against (I used an elevated counterpoise with a 'tuner' to resonate it for the band I'm using). That places the current peak of my antenna at the bend on 40, which produces a heavy mix of vertical and horizontal polarization. Stations within 1000 miles can't tell the difference between the "L" and my doublet. Stations much past 1000 miles can't hear me on the doublet while they copy me Q5 on the "L". It also works on 80, although its short length really limits its efficiency there. Still, I often work stations out to 1,000 mi on 80 running 100 watts CW. I used the same technique Stuart mentioned to bring the wires into the shack where I have a sash window by the operating desk. I cut a strip of expanded foam about 1 inch high and as wide as the sash to fit tightly under the window. A stick cut to length goes from the top of the sash to the top of the window frame where it wedges to hold the window tightly down against the foam (and keep the window from being opened from the outside). I picked up some 1/4 inch plastic tubing at Tap Plastics that I poked through the foam to provide "feed throughs" for the feeder and counterpoise wires. The tubing is stiff and protects the foam from being cut and torn by the movement of the wires. If I get too many holes from making too many changes, I just replace the foam with a new strip. Very little air can slip through the tubing with the wires in them. You can always add a dab of silicon grout or a wrap of tape to completely seal them if desired. That results in very little insulation efficiency loss with the thick strip of foam filling the gap. Like every antenna in every station, this one is a compromise. Perhaps mine is more of a compromise than many, but it's less than many others have to live with. And it works very well. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
