Topband: Air wound coil

[donovanf at starpower.net]

Hi Jim, 


If you base load a 68 vertical on 160 meters it will create very 
high voltage at the base of the vertical which may damage the 
base insulator. Much better to use top loading to avoid high 
voltage at the base. 


73 
Frank 
W3LPL 

----- Original Message -----

From: "Jim Garland" <4cx250b at miamioh.edu> 
To: topband at contesting.com 
Sent: Sunday, September 2, 2018 10:03:32 PM 
Subject: Re: Topband: Air wound coil 

On this general topic, I'm erecting a 68 ft aluminum self-supporting 
pole (DX Engineering) that is four inches OD at the bottom, tapering to 
about 1/2 inch at the top. It is designed as a full size 1/4 wave 80m 
vertical. I'd like to use it on 160m. If I add four capacity hat wires 
at the top, would that sufficiently lower the resonant point? The 
antenna tilts at the base with a hand winch, so it's not hard to add or 
remove wires if I want to restore the antenna to 80m. The other option 
is to add inductance at the base (easy to do), but I don't know if that 
is the preferred solution or not. BTW, there are sixty 30m radials 
already installed at the base, from a previous antenna. I only care 
about resonating the antenna near the low end of the band. Except for 
cacti and coyotes, the antenna is 200m from any structure, fed with 
buried hardline. Any suggestions? Thanks! 

73, 

Jim W8ZR 



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