Topband: Topband Digest, Vol 45, Issue 17

[Jim Brown]

On Mon, 18 Sep 2006 12:43:00 -0400, Herb Schoenbohm wrote:

>Suggest a resonant circuit with a 50 ohm feed line tapped up a few
>turns from the grounded side.  Since this is outside a small WX 
>proofed plastic box of the appropriate size may be needed.  Also
>you might consider, depending on you ultimate power levels, 
>determining the required C needed with the coil with a low power
>capacitor and then switching in a good Mica HV cap such as a G2.
> This antenna you describe should be a real performer on 80 meters.

Yes, after I posted the question, I went "into the woodshed" -- 
looking through ON4UN's book and the Antenna Book, and found exactly 
that suggestion for a very similar configuration. So I built it up, 
winding the 9 turns of #16 enameled wire around a 2" piece of PVC 
plumbing pipe (it's the biggest enameled wire and coil form I had in 
the junkbox), tapped it up a bit under 2 turns, hung a HV 
transmitting cap across it, and fired away. It loads, but something 
in what I built is VERY unstable over time with applied power so the 
Z doesn't stand still long enough for the tuner to load it. I 
changed the cap, so I suspect the coil form. I felt it carefully 
after hitting with 500w for a 30 seconds or so, and didn't feel any 
heat. Strange. 

I'll try it again with bigger wire that doesn't need a form. 

Thanks and 73,

Jim K9YC