[TowerTalk] Making an 80 meter vertical from Rohn 25

[Jim Brown]

On Wed, 23 Dec 2009 14:00:39 -0500, Rex Lint wrote:

> Wouldn't a hefty variable work just as well?  $15 compared
>to $80 or so?

You're correct -- when you're feeding at a low impedance point 
(near a quarter wave from the open end), it's not voltage, it's 
CURRENT and dissipation (LOSS). A local surplus house here in 
Silicon Valley has a lot of HV rated capacitors in bins. I bought 
a bunch of them to use for things like this, but I didn't have 
easy access to data sheets to learn about their equivalent series 
resistance. My solution was simple -- I tried various parts at 
the feed point of my 160M vertical that needed series capacitance 
to match it, keyed the legal limit amp for a while, and then went 
outside to see if they were cool, warm, hot, or smoking. 

All the capacitors I tested were rated for 3kV or more, but some 
smoked and some ran quite cool 

73,

Jim K9YC