Spice model of inductor including stray capacitances:
Simulation.
Red=input voltage
Green=input current
Blue=load voltage
Yellow=load current
This system (including reasonable leakage capacitance) representing a 50 ohm
source driving a 100uH inductor with stray capacitance of 9pF and a 50pF load
(small whip), shows input and output currents are essentially equal, while
output voltage greatly increases at resonance.
In the following SPICE plot, increasing stray capacitance shows expected
departure from equal input and output currents. Distributed capacitance to
ground is now at 45pF, nearly equal to the 50pF antenna capacitance:
Again despite stray capacitance nearly equaling load capacitance, current
levels at input and output are reasonably similar:
Green=source current
Yellow=load current
Red=source voltage
Blue=load voltage
If we multiply output voltage times current, the apparent power is many
dozens of times the input power. The reason is simple, phase relationship
between voltage and current along the inductor changes even while current
remains essentially uniform.
Although casual experimenters often assume a loading coil
“replaces” the missing length in an antenna and has sinking voltage
with rising current, this is not the case unless stray capacitance is extreme or
the inductor is incorrectly and inefficiently operated at or near self(series)
resonance. The loading inductor really just corrects power factor, and bringing
voltage and current into phase at resonance. It does replace missing length by
simulating an antenna.
Linear loading is no different, it simply behaves like a very lossy lowQ
coil and does not add radiation to the system. Unless of course we are talking
about heat radiation.
