[AMPS] Big Amps and Antennas

[measures]

>
>Hello,
>Since starting to use my "big boy" amp, I have had more antenna problems 
>than in all my 40 years + of ham radio.
>Examples:
>1. Those cheap black plastic insulators commonly sold at hamfests melt. 
>The result is the antenna falls.

Amen

>
>2. A small tree branch (1/4" dia.) fell from a tree and was hanging from 
>the end of the antenna (I just happened to notice this). The first time I 
>put power to the antenna, the 12ga stranded copper wire melted at that 
>point and the antenna fell down. I found the small branch on the ground 
>and it showed signs of having been  on fire.
>3. The latest happening is the strangest (I swear it is true). After 
>tuning up the amp into a dummy load, I switched to the antenna to fine 
>tune the amp settings. While fine tuning, everything looked normal then 
>all of a sudden, all the amp meters went wild. My first thought was "damn, 
>one of those paracites, how will I ever get rid of it". Then I went back 
>to the dummy load, and every thing was back to normal. I immediately went 
>out into the yard and found the antenna on the ground. The 12" by 1" 
>ceramic end insulator was broken at the antenna end. I could not visually 
>find any defects in the insulator at the failure point.
>
>Is all this being caused by corona effects? 

my guess is yes.  

>What could be the max voltage 
>at the antenna ends? 

Depends on wire gauge and watts.  

>Copperweld appears to be the only way to go for wire, 

If one provides support for the center of the dipole, TW wire is strong 
enough.  

>but what should I be using for end insulators?
>Any insight would be greatly appreciated.
>
After too many meltdowns/fires, I wound up using 1/8" Teflon  sheet stock 
for the end insulator.  The length needs to be about 18" and the width 
about 1.5 inchs.  A leather punch works ok for making holes.  To minimize 
corona, solder a 6" diameter loop of copperweld at the end of the 
antenna.  //  The weird thing about corona is that most of the melting  
does not occur at the end of antenna wire.  It happens several inches 
beyond the end.  


cheers, Bruce

-  Rich..., 805.386.3734, www.vcnet.com/measures.  
end


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