Antenna efficiency (as opposed to antenna system efficiency) has little
to do with resonance, but a lot to do with its radiation resistance
relative to its loss resistances.
A resonant dipole with a feedpoint impedance of 70+j0 which includes
copper losses of 1 ohm has an efficiency of 69/70=98.6%. A non-resonant
dipole with a feedpoint impedance of 70+j1000 has exactly the same
efficiency - 98.6% !!
And just to end with some nonsense: a monoband antenna can only be
resonant at one spot frequency - so don't speak into the mic, or press
the key, because those sidebands you generate will be on frequencies
where the antenna isn't resonant :)
73,
Steve G3TXQ
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