[Elecraft] Big Coax on Dipoles

[Steve Ellington]

The feed point on some of those bands would see a 150:1 swr (no kidding)! 
Your efficiency would be about 5%. Your tuner would still  see a low swr and 
it will be an easy match because of the tremendous loss in that 100 pounds 
of coax. Sure you can work stations, with that height you could QSO with a 
light bulb,  but you would be 100 times stronger using ladder line plus you 
wouldn't need 95 pounds of sand to hold up that lossy dummy load coax.
I'm feeding a 200' doublet with ladder line then to a 4:1 current balun next 
to the K3. The K3's internal tuner finds a match on 160-6 meters and I have 
very little power loss on any band. Now if I could just find a fertilizer to 
make my tree grow another 50'!

Steve
N4LQ
N4LQ at carolina.rr.com
----- Original Message ----- 
From: "Jim Brown" <jim at audiosystemsgroup.com>
To: "Elecraft List" <elecraft at mailman.qth.net>
Sent: Wednesday, July 22, 2009 1:03 AM
Subject: [Elecraft] Big Coax on Dipoles


> On Fri, 17 Jul 2009 09:19:03 +0100, Geoffrey Mackenzie-Kennedy wrote:
>
>>orgetting about RF performance for a moment, wouldn't the weight of RG-8/
>>RG-213 create a problem unless the antenna is supported at its feedpoint ?
>
> I have four fan dipoles suspended at 100-120 ft between tall trees
> (redwoods), all fed with RG8 or RG11. There is no problem supporting the 
> big
> coax. The keys to success are robust mechanical construction so that you 
> can
> establish high lateral tension. If one of the objects you're suspending 
> from
> is a tree, one end needs a weight and pulley to adjust to wind conditions. 
> I
> use 6.5 gallon water jugs filled with dry sand (roughly 95 pounds), and 
> the
> trees are typically 140-220 ft apart. I use 5/16-inch dual woven poly 
> rope,
> #10 solid copper, and robust insulators. Do they sag? Sure -- at least 10 
> ft
> on the long dipoles. Does it matter? No.
>
> One of the side benefits of the big coax is that my 80/40 fans (at right
> angles) work quite well on 30M, 17M, 12M, and 6M, thanks to the lower loss
> with moderate degrees of mismatch. With relatively litte time on 6M, I've
> made nearly two dozen QSOs of more than 2,500 miles with my K3 and one of
> those dipoles.
>
> 73,
>
> Jim Brown K9YC
>
>
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