Topband: Spiral Top Hat

[PaulKB8N at aol.com]

Gang,
 
Thanks for the info on radials, I've put out a bunch of short ones around  
the base and a few longer ones wherever they would fit.
 
KV8Q's very respectable ARRL 160 score using the K6MM short helically wound 
 vertical got me thinking about building one.  While Googling information  
about short verticals, I stumbled across an article about spiral top hats.   
I was intrigued that many of the lowfers use these on their transmit 
antennas  with great success.
 
The recommended amount of wire for the spiral is about one quarter  
wavelength.  I built a 4' by 4' X frame out of PVC pipe and was able to  wind a 
spiral that used about 115' of wire.  I put it on an 8' mast over my  ground 
field  and found it to be resonant at 2.3 MHz!  2:1 bandwidth  was about 
15KHz. I did not attempt to put it on the air, but the results suggest  that a 
slightly larger spiral tophat or a somewhat longer mast would produce  
something that might be resonant on 160M.
 
While I realize that an 8' vertical may not produce outstanding  results, I 
wonder what the downside is to this type of tophat on taller  verticals.  
It would seem better to resonate the antenna at the top, where  currents are 
lower, than using base loading.  What is the verdict?
 
Paul, K5AF