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Stacking 5/8th-wave 2-meter elements x4
Sometimes it's just fun to see how far...
http://home.comcast.net/~buck0/outpvccm.html This link brings you to a collection of e-mail exchanges outlining the construction of a collinear 5/8th-wave 2-meter vertical. Insights, discussions and inovations on 2, 3, and 4 stacked elements. Several great images too. Special thanks to Paul Anderson N8CVW /7. He took some ideas I played around with (and posted on the WWWeb over 6 years ago) and really went hog-wild!! http://home.comcast.net/~buck0/5-8thx2j.htm Hope you'll see there is still some fun to be had in the hobby, in the ways of antenna modeling! 73 Steve KB1DIG |
On Sun, 20 Feb 2005 16:15:44 -0500, "Kim & Steve Merrill"
wrote: Special thanks to Paul Anderson N8CVW /7. He took some ideas I played around with (and posted on the WWWeb over 6 years ago) and really went hog-wild!! http://home.comcast.net/~buck0/5-8thx2j.htm I wonder what his 6dB gain reference is? Danny, K6MHE |
Danny, K6MHE wrote:
"I wonder what his 6 dB gain is" There is a "Super J" antenna on page 16-27 of the 19th edition of the "ARRL Antenna Book". The book says the two stacked 1/2-wave collinear elements provide about 6 dB gain over a 1/4-wave whip antenna and about 3 dB gain over a 5/8-wave antenna. I won`t speculate that you actually get more gain from (2) stacked 5/8-wave sections, but it`s possible. Maybe 3 dB more, like a single 5/8-wave over a single 1/4-wave. 6 dB over a 1/4-wave whip is 8.14 dBi. The 1/4-wave whip has a gain of 2.14 dBi Best regards, Richard Harrison, KB5WZI |
6 dB over a 1/4-wave whip is 8.14 dBi.
The 1/4-wave whip has a gain of 2.14 dBi ....... The half wave vertical should have that 2.14 dbi gain. A 1/4 wave ground plane should show about .3 db less... Or when modeled anyway.... In general, a properly designed dual 5/8 collinear should have appx 5.1 dbi gain. Or appx 3 dbd.... And yes, that is slightly more than the dual 1/2 collinear should do. If a single half wave shows 2.15 dbi, I wonder how adding a second element can add another 3.85 db gain...??? Myself, I think their gain numbers are a little happy... Also, in that super J article, the 1/4 wave and 5/8's they compare to are mobile whips...This would greatly skew any comparisons with the super J, being it's not a mobile antenna. IE: make it look better than it really is... An average elevated 1/4 GP will show appx 1.8 dbi or so...Only about .3 db difference from a 1/2 wave that is elevated. Of course, in the real world, the results can vary greatly due to decoupling, or the lack of, etc... I'd have to check/model the gain of the super J, but I'm almost sure it would be less than 5.1 dbi...I'll take a wild guess and say maybe .6 db less??? MK |
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I was using elnec in that example. But I was using "free space".
I was trying to leave the ground out of it... Also those models were all elevated at 40 ft at the base. At that height using real ground/average, it had about 3.8 dbi at 8 degrees. In comparison, the 1/4 GP with sloping radials did about 1.8 dbi free space. Real ground at 40ft, was about 3.0 dbi at 9 degrees. So about .8 db difference using real ground. The main reason I was sort of skeptical about the 3.85 db increase was due to your next to the last statement. I didn't think the close spacing would give that much gain. As I quick test, I just tried adding another element above the original, in that model. I used 2 sources to feed. With the very close spacing of the two elements, the free space gain was 3.59 dbi...A tad less than I expected... The real ground numbers were 5.53 dbi, at 7 degrees. So almost a perfect 2 db increase in that model over real ground. As a comparison, with about a 1/2 wave spacing, I got 7.23 dbi using the same real ground. About 3.4 db increase...Could probably get more with a wider spacing... It's this spacing thing that made me dubious... I couldn't see 3.85 extra, being the elements were very close using the stub. BTW...all the models I had were for 10m, at 40 ft.... MK |
Roy Lewallen wrote:
What modeling program are you using that gives those results? A half wave vertical over perfect ground has about 5.15 dBi gain at the horizon. . . Correction -- a *quarter* wavelength ground-mounted vertical has the gain I quoted. A half wavelength ground-mounted vertical has a slightly narrower pattern, resulting in a little more gain over perfect ground. It's about 6.9 dBi at the horizon. Roy Lewallen, W7EL |
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