Bob,
I know folks use vacuum variables at the feedpoint of verticals, but I don't
understand why. It's a fairly low impedance (and therefore low voltage)
point, isn't it? Wouldn't a hefty variable work just as well? $15 compared
to $80 or so?
Rex
K1HI
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of bob finger
Sent: Wednesday, December 23, 2009 6:10 AM
To: Brahmangou@aol.com
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] Making an 80 meter vertical from Rohn 25
Get hold of a copy of ON4UN's Low Band book. It is available from ARRL.
Johns book is considered the bible for low band antennas. That book will
tell you that a 12 inch tower will be resonant on 3500 if it is about 64
feet long, and a tower about 78 feet long feeds easily with some series
capacitance in the feedpoint. A vacuum variable of about 1000pf should allow
you to easily tune to any point on the 75/80 band.
All assumes 5 ohms of loss in the radial system. 73 and Merry Christmas
bob de w9ge
>I'm wanting to put up a full sized 80 meter vertical made from Rohn 25
>in my pasture.
>Marty Haley AB5GU
>
>_______________________________________________
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>_______________________________________________
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--
Bob Finger
8511 Swann Haven Road
Easton MD 21601
cell 703 408-2176
e-mail to: Finger@GOEASTON.NET
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