[TowerTalk] Making an 80 meter vertical from Rohn 25

[Jim Brown]

On Wed, 23 Dec 2009 14:38:51 -0500, Chet wrote:

>My $15 variable worked "as advertised" just like you have suggested. Even
>though I had mine in a sealed container, I had rust on all the plates in 
>About 3 months. Shaft started to be hard to turn in 6 months.

Many antenna systems don't need a variable capacitor at all. I modeled my 
160M vertical antenna, tweaked the length so that the feedpoint impedance 
would be 50 + jxxx ohms, then plugged in fixed capacitors to hit -jxxx 
ohms, and then added or subtracted small fixed capacitors in parallel to 
give me less than 2:1 over the part of the band I wanted to operate. It 
took me less than an hour to do that tuning, including the time to 
mechanically build the capacitor bank. 

If I were to add an 80M element, I'd switch in another matching network 
for it. 

73,

Jim K9YC