HI Fred,


On 11/07/2020 04:57, Fred McKenzie wrote:

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)

Kristoff-

Are you over-thinking this? The power is lost in resistance. For a
great mis-match, currents might be very high in the tuner.

Well, that's the question. (As noted, this is why we called it
"fundamental Fridays" :-) )


The reason I kind-of ignored resistive loss as that component is not
relative to frequency while the efficiency of an antenna+antenna-tuner
system is clearly frequency dependent.


It is however an interesting thought that power-dissipation due to
resistance can be frequency-dependent via its current.

But would this not mean that the efficiency of tuned antenna would be
dependent of the design of the tuner and that a theoretical
antenna-tuner without resistance would have 100 % efficiency.

I have not found this in any documents I have been reading on this.




Suppose you have a lousy antenna where 50 percent of your power is lost
in the transmission line and tuner. Anyone listening to you would
suffer a 3 DB reduced signal compared to the ideal antenna. That is one
half S-Unit. They probably would not know the difference.

OK, but you can just as easy apply this for -say- an antenna for 475 or
137 KHz band where the efficiency of the antenna-system is ... euh ..
less then 50 % (unless you have a very very very big garden :-) )



Also your lousy antenna may have a poor pattern, transmitting your
signal in the wrong direction. The tuner can not fix that.

That's true and if this was the only effect playing here, then an
antenna-tuner would not have a lower efficiency then a fully matched
antenna, just a different radiation-pattern.

But we all learned at the ham-radio academy that a tuned antenna has a
lower efficiency, no?
Or where things wrongly represented at the ham-radio lessons?




I know. We have been chewing on this question for some time too and
so-far have not come up with an answer neither.

Every answer seams to produce as many counter-arguments.
(I guess that what you get from asking "fundamental" questions) :-(







Fred

Kristoff - ON1ARF