In article , kristoff
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.

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.

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

Fred

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

kristoff wrote:
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.

Well, with so many assumptions already cast in stone, there is not
very much to discuss anymore, right?

In article , says...

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.




The loss in the tuner is the loss in the components, mostly the
resistance of the coil. It could be some in the capacitors if they are
not a air or vacuum variatables ( switched in capacitors sometimes used)
It could also be in the internal wiring.

Tuners are only optimised over a small band of frequencies and
impedances. If one designs the tuner to be the best at 14 MHz, then the
coil and capacitors will be too large or too small at other frequencies
for optimen power transfer. That is often referred to the Q of the
circuit. YOu start to get larger and larger circulating currents in the
tuner and the losses go up due to the resistance of the coil and wires
in the tuner.

Look at transmitters of the old tube circuits. The plate circuit is
designed for a Q of around 10 to 12. That seems to be the best
compromise between the harmonic reduction and efficency. Go one way and
the losses go down, but the harmonics go up. Go the other way you
reduce the harmonics but the efficeny goes down.