Hi Rob, Jim, Jef, all.



Thanks for continuing on this small thread.
As said, I asked this as a fundamental" question, so I am really
learning a lot here.


(see inline comment)



On 15/07/2020 16:27, Rob wrote:

Antenna Matching Units ( I prefer not to use the word "Tuner") do have
fixed resistance in inductors and wiring as has been stated in this thread.

No! The amount of inductance varies depending on how much of the
inductor is used, thus the resistance of the unit varies with the
setting.

OK. makes sense.


Resistance also varies with frequency since the skin effect
is "deeper" (lower resistance) with lower frequency.

Correct me if I am wrong, but it looks to me that these two elements
(partly) counter each other.

To tune / match an antenna for a lower frequency, you need more inductor
wire (i.e. greater resistor), but the skin-effect will be lower.





BTW. I always had the idea that skin-effect was only important for
frequencies of VHF and higher, not for HF.


Are there figures of how much resistances the skin effect adds to a
wire, in respect to the frequency?

(Just to get an idea of the scale of things)



And, the antenna resistance to be matched also varies. When the
antenna is too short it will have a lower resistance
This is something I do not completely understand.


I guess you are talking the radiation resistance, correct?

As far as I understand it, the radiation resistance is a "virtual"
resistance which is created by the fact that an antenna converts
electrical energy in electromagnetic waves that are radiated, thereby
extracting energy from the wire.
This "loss of energy" in the wire is modelled as a virtual resistance.


So, saying "a short antenna has a lower resistance then a full-size
antenna", is then the same as saying "a short antenna emits less energy
then a full size antenna", which is equivalent to "a short antenna is
less efficient"



So isn't this a circular reasoning?



What exactly is the reason that a short antenna has a lower resistance?



.., and thus any fixed
losses in tuner and feeder will have a higher relative
effect.

So, are there are then two different effects at play he
- the resistance of the tuner/matching unit which changes with frequency
due to the practical way it is build
- the radiation resistance of the antenna that changes with frequency.





All in all it is a completely wrong assumption that the losses will
be independent from frequency, even when te resistive values in the
tuner would be the same.


73
Kristoff - ON1ARF