Don, K6MHE wrote:
"Where did you come up with that one?"
(A response to my statement that a receiving antenna must be resonant to
enable full acceptance of available energy)

I`ve tweaked antenna trimmers which dramatically boosted the signal when
reasonance was reached. I`ve seen grounded 1/4-wave structures near a
broadcast station detuned, thus eliminating the distortion they had
caused in the station`s radiation pattern. If they`re not resonant, they
don`t accept enough energy to make any difference in the station`s
pattern.

!/2-wave wires in free-space are resonant. Resonance is defined as unity
power factor, that is, XL=XC. At resonance, reactance is balanced out
and only resistance is left to oppose current in a wire. Usually the
wire has a radiation resistance which is large as compared with its loss
resistance in practical antennas.

At frequencies below first resonance, the ungrounded wire is less than a
1/2-wavelencth. It has a low radiation resistance and a high capacitive
reactance. We can add inductance to tune the wire to resonance.

At frequencies above first resonance, the ungrounded wire is more than a
1/2-wavelength, and if it is not much longer, the wiire has an inductive
reactance. The phase flip-flop at resonance is abrupt and the reactance
is an impediment to the current on either side of resonance. The correct
series capacitor can be placed in series with the roo-long wire to tune
out its excess inductive reactance.

A mechanical analog is the vibrating-reed frequency meter used at power
frequencies. All the reeds are in the power-frequency field. Only the
reed of resonant length has so little opposition to the excitation that
it vibrates freely.

A versatile antenna tuner can insert either inductive or capacitive
reactance in series with an antenna to correct its power factor (tune it
to resonance) so it can accept maximum excitation.

Best regards, Richard Harrison, KB5WZI