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Old April 5th 04, 08:56 AM
Mark Keith
 
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"Dave VanHorn" wrote in message ...
"Mark Keith" wrote in message
om...
George Cronk wrote in message

. 154.205...
Does anyone know where I can get plans for this antenna? Materials

needed
to build one?

Thanks


You would be better off with a 1/4 wave ground plane on 2m. Seriously.
And one of those can be as simple as five 19 inch pieces of wire and a
So-239 connector. MK


Why would he be better off with a 1/4 wave, with it's large vertical lobe?


Cuz it's easier decoupled with it's 1/4 wave radials, and is less
likely to have feedline radiation than the funky 5/8 antenna with 1/4
wave radials. In direct comparisons here, the 1/4 GP was a good bit
better than the 5/8 with 1/4 radials. The maximum gain of an elevated
1/4 wave GP on 2m, mounted at 35 ft at the base, is appx 6.2 dbi at 3
degrees. The maximum gain of a 5/8 GP with horizontal 1/4 wave
radials, at the same height, is about 4.7 dbi at the same angle. And
this does not yet take into account any decoupling problems! If the
feedline radiates, any gain on the horizon is likely lost as the
pattern is skewed up off the horizon. The average 5/8 antenna is
ruined by using 1/4 wave radials. A 5/8 should be paired with a mirror
image 5/8 to function properly. IE: dual 5/8 collinear such as the
isopole, etc...
And decoupling must still be used even on those. I agree with one
thing Richard said about height and a 1/4 wave..If you get the tip of
the 1/4 GP at the same height as the tip of a tall dual 5/8 collinear,
there is little real difference between the two. And the dual 5/8's
collinear is better than a 5/8 GP. 2m is real critical as far as the
low angles used, and also to the effects of feedline radiation
lowering the gain at those low angles. Now on 10m, many times I do
prefer a 5/8 GP over a 1/4 GP, but there the angles used are less
critical.
If your 5/8's works, I wouldn't worry much, but in comparing them in
A/B tests, "at appx 35 ft" I've never seen a 5/8 GP with 1/4 radials
beat a 1/4 wave GP with 1/4 radials. I once built a fancy 5/8 GP with
a nice larson coil, lots of 1/4 wave radials, etc...Was a super
dud...I tore it up the 1st day and went back to a 1/4 wave. The 1/4
wave was an average 3-4 S units better on local rptrs, and simplex.
About the same difference as comparing a undecoupled ringo ranger, to
a decoupled ringo ranger 2... MK
 
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