Hi all,


Months ago, when the C-word was something still something far away in a
distant land, we had a small discussion in our radio-club.
The idea was this: "fundamentals Fridays"(*), a chance to ask questions
on aspects of amateur-radio that we all know that are true, but nobody
seams to be able to explain why exactly they are the way they are.



One of the questions that popped up is this: (although I am not sure of
this is a question about physics or about antennas)


It is "common knowledge" that when using an antenna with an
antenna-tuner, the efficiency of an antenna goes down: the smaller the
size of the antenna compared the wavelength, the less power is emitted
and the more power is "lost in the tuner".

But, why is that?
Where does this "lost" energy go to?




In essence, the goal of an antenna-tuner is to do impedance-matching:
match the impedance of an antenna at a certain frequency to the (50 ohm)
output impedance of the transmitter and the transmission-line. For that,
it uses inductors or capacitors. (although I know that these components
do also have a resistive part, but I think we can ignore this here)


Now, I understand that a capacitor can "store" energy in the electrical
field between the two plates, and an inductor uses electrical fields to
create a current to counter changes in current, ... but why does this
create a "lost" of energy?

In what form is that energy then "lost"? Is it converted to heat? Is it
"emitted"?


I've been reading about the "Radiation resistance" of an antenna (**)
and, although I am not a physicist, I kind-of understand the notion of
the transfer of energy from the momentum of an electron to a photon.

But physical process is at work inside an antenna-tuner?
And to what kind of energy is the "lost power" converted? Heat?

Does an antenna-tuner actually heat up?
(again, ignoring the "resistive" loss of the components of the tuner)




(*) Fundamental Fridays: (c) EEVblog

(**) https://en.wikipedia.org/wiki/Radiation_resistance


73
kristoff - ON1ARF