A 1/4 wave of wire is resonant at double the frequency it was when grounded -
because that is the frequency at which it is a 1/2 wave long...
Example: -> A 33 foot 1/4 wave vertical for 40 meters, if lifted from ground
is instantly a half wave dipole for 20 meters, and is not resonant on 40...
It is resonant on 40 when attached to ground because the ground is the mirror
image for the missing 33 feet... So, the rule of thumb to remove a wire
"electrically" from the near field - If it is a 1/4 wave long lift it off
ground... If it is a 1/2 wave long , ground it...
(Mnemonic is: Quarter waves float and half waves sink - Copyright @ K8DO)
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With an antenna like a 4 square you simply "float" the other three
> verticals in order to get them out of the picture while you're tuning
> the 4th vertical. These three floating verticals are almost exactly
> resonant with the one you're interested in.
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Denny
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