Towertalk
[Top] [All Lists]

## [TowerTalk] Multiband dipoles

 To: [TowerTalk] Multiband dipoles n4kg@juno.com (n4kg@juno.com) Thu, 25 Oct 2001 17:00:36 -0600
 ```There are several approaches to making multiband dipoles. Two dipoles at right angles to each other will have almost ZERO coupling / interaction. Three dipoles spaced 60 degrees to each other have slight coupling / interaction. Using traps for several bands reduces efficiency and bandwidth. One way to minimize this effect is to use 2 dipoles and split the traps, say 10 and 20M traps plus 80M and 15M traps plus 40M. Then separate the ends as far as possible. Force 12 uses 'open sleeve' coupling for their driven elements on their triband beams. K9AY published an article on a 3 band wire dipole for the WARC bands in RF Design several years ago (Nov 1994). He suggests conductor spacing (d) according to this formula: Log (d) = 0.54 x Log (D/4) where D = conductor diameter (assuming equal D for each element). One of my favorite multiband dipoles is simply a 20M dipole (17 ft each side) fed with ladderline and a balanced tuner. This antenna has a figure 8 pattern from 10 through 30 M. Beamwidth varies from 50 degrees on 10M through 90 degrees on 30M. 30M performance can be improved slightly by using 20 ft on each side with the addition of 4 minor lobes on 10M and slightly more narrow main lobes on all bands. An 80M dipole can be used on 80, 30, 17, and 12M fed with coax since the center feedpoint corresponds to a current maximum on those bands. Patterns correspond to a 3/2 Wavelength (WL) Long Wire on 30M, 5/2 WL LW on 17M, and 7/2 WL LW on 12M. SWR < 3:1 on 30M, and <2:1 on 17 and 12M. With ladderline feed, an 80M dipole can be used on all bands from 80 through 10M. It will act as various types of long wires on 30 through 10 meters. The feedpoint corresponds to voltage maximums on 40, 20, 15, and 10M and current maximums on 80, 30, 17, and 12M. Tom N4KG ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: http://dl.www.juno.com/get/web/. List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems, Trylon Titan towers, coax, hardline and more. Also check out our self supporting towers up to 100 feet for under \$1500!! http://www.anwireless.com ----- FAQ on WWW: http://www.contesting.com/FAQ/towertalk Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com ```