Bill is right in what he remembers about radial numbers. For quarter wave
60 brings you most of the good results. There is very little improvement
above that.
When you increase the length of the radials, (and the vertical is not
commensurately longer), you are only going to couple more to RF lossy earth,
(higher capacity of a half wave radial vs. quarter wave one to the earth).
Thus, to keep the losses down you need more half wave radials to intercept
the fields of the vertical than if you used quarter wave ones.
What is often overlooked by hams is the main effect you want is to intercept
the return currents of the vertical from all directions and return said
currents to the antenna base to complete the circuit with lowest loss, NOT
relying on earth returns.
Again, for multiband verticals that are "fat" like the Hy Tower, you could
use quarter wave or less.
If you used shorter than quarter wave resonant radials, you could always
bring them to resonance by use of series loading inductance as outlined in
the Les Moxon book from RSGB, (Sold by ARRL).
-Stuart
K5KVH
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