Francesco L. wrote:
I was wondering if it's possible to shorten the radials from the standard
1/4 wavelength to another value, a smaller one. For example, in a 20 meters
antenna, which is the best value of length for shortened radials or, in
alternative, until which value is possible to go to without superlosses?

If radials are buried, their velocity factors may be
something in the ballpark of 0.5. That's certainly a
shortening effect.

With elevated radials, the radials can be shortened
and the vertical element lengthened to maintain
resonance. Radials can also be shortened by loading
each radial with a coil.
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73, Cecil http://www.w5dxp.com