Fred N3CSY asked: I'm another limited space, restricted community ham (for now). I've been considering different types of verticals which might be best. I THINK, I'm looking for an antenna which:
- vertical ? - no radials - no counterpoises - no guy-wires - 40 thru 10 - maybe 4 shorter buried radials (if I must) - not a lot of "visual" space, for neighbors We have a MOBILE Home (mostly plastic, and wood) - which sits on a slab of concrete, surrounded by 8x8 wood timers, 2 feet high on front side of mobile. Can easily get UNDER mobile, thru removable siding. Park owner, OK'd a "marine antenna" - whatever that means to him. We live on shore of St. Lawrence River - Canada in the distance. What commercial or home-made antenna could suit my bill? ------------------------------------ To most people familiar with ships a "marine" antenna is a 20 foot whip, usually a robust self-supporting fiberglass pole that is mounted with side brackets on the side of the house on smaller boats or on the side of one of the stack on large ships or, on large ships, is mounted at the base with a ring about 1-foot in diameter that is bolted to the steel deck. They work FB as Marconi antennas (1/4 wave or shorter worked against ground) because the "ground" on a ship is the best you'll find on the earth: miles and miles of salt water. With such a ground those antennas are astonishingly effective. A big part of the efficiency comes not from the immediate ground connection, but from the fact that out in the Fresnel zone some wavelengths from the antenna where the electromagnetic waves interact with the earth, the "earth" there is very good conducting salt water. Your requirements include "no radials". In that case you might go with one of the so-called "ground independent" verticals such as the Cushcraft R6000. They are electrically 1/2 wavelength long, so they don't require radials but they are *not* as efficient as a true half-wave antenna. Still, a 40-10 or 40-6 meter antenna like the Cushcraft is only a bit over 20 feet tall, which should meet the demands of the park owner, and will deliver good performance in the smallest space. The only issue will be that instead of the clean, simple fiberglass pole that one usually sees on boats, these antennas have several vertical sections all interconnected. On land you'll need radials with a typical marine whip. The closer to the ground, the more radials you'll need for a given efficiency. The idea of the radials is to intercept the RF currents and have them flow in good conducting copper instead of through the lossy earth. If they have to be on the ground, the "rule of thumb" the FCC and broadcast engineers have used for over half a century is to have 120 radials 0.2 wavelengths long radiating from the base of the antenna. If you can raise the radials even only five or six feed above the earth, half a dozen are just as effective as the 120 on (or in) the ground. Fewer will work, but not work as well. Such an antenna with, say, four elevated 1/4 wave radials, will work quite well on 15 and 20 meters, work fair on 40 meters and even provide some contacts on 80, although there it'll be a very inefficient antenna. 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
