Topband: toploading of shunt fed tower

[Doug Waller]

>Summation, the Force 12 C4XL on top of an elevated, insulated
>base, series fed Rohn 25 tower provides capacitive top loading
>equivalent to approximately 35 feet

As additional info, F-12 states that the 40m, 20m and 15m reflectors may be 
grounded to boom for additional toploading, without any effect to C4XL 
performance.  This gives more toploading, and an extra dimension of resonant 
frequency fine tuning.  P5 and VU4 were worked, verifying C4XL performance 
with the grounded reflectors.

For those of you planning to topload a short tower for 160m, the Zig-Zag 
topload works well.  Mine is a 16 ft tall aluminum mast, with another 80 
feet of wire zig-zagged up and down around the mast four times, in linear 
loading configuration.  The zig-zag topload is mounted above the C4XL beam, 
shifts only 10m center freq slightly, and yields two resonant frequencies, 
in my case, one at 1.78 mHz, the other at 2.12 mHz.  The effect of this is a 
very broad 1,8:1 to 1.8:1 SWR bandwidth across the whole 160m band.  Another 
advantage is that there are no sloping topload wires to contend with.

73, om Doug / NX4D