View Single Post
  #3   Report Post  
Old May 13th 04, 09:52 PM
Jim Kelley
 
Posts: n/a
Default



Cecil Moore wrote:

Theplanters95 wrote:
The article in the May 2004 issue of QST on ppg 28. It is for a shortened end
fed 1/2 wave 80 meter antenna. How well does this antenna perform.
Will it be an effective multiband antenna for 80m - 10m?


Here is a rule of thumb that you can take to the bank. If an shortened
80m antenna has loading coils, it will not perform well on the higher
bands. Why? XL=2*pi*f*L - do the math. XL *increases* proportional
to frequency. For antenna efficiency, you NEVER want XL to be more
than you need. And there's something called self-resonance where
XL=self-XC, a terribly lossy condition where the coil current is
sky high.


This is one of tricks that Mother Nature plays on us hams. XL goes
the "wrong" way with frequency but (pardon my Russian) "tough ****sky",
that's the only way it goes.


Could a loading coil be used more like a trap?

73, ac6xg