"Antonio Vernucci" wrote in
:

....
I raised the above arguments just as a confirmation of the fact that
understanding what to do before attempting to adjust antennas is not
that easy.

Well, it was easier until people that don't understand the fundamentals
of transmission lines got access to instruments that measure R and X, and
used their new found capability to prop up the "resonant antennas work
better" myth.

For many common ham antenna *systems* (eg a length coax feed to a centre
fed, approximately half wave dipole using an effective balun), system
efficiency is best when transmission line losses are least, and
minimising line VSWR is a good first cut for best efficiency. Having done
that, an ATU at the tx to transform the load to that required by the tx
so that it can deliver its rated power with specification linearity may
be needed.

If you drill down on the resonance myth, its greatest validity is that
for some types of antenna systems (including the one described above),
resonance delivers a low VSWR, approximately the minimum VSWR, and in
those systems leads to approximately lowest line loss, resulting in best
efficiency. Nothing to do with the 'technical' explanation that I heard
the other day that a "resonance antenna fairly sucks the energy out of
the transmitter". It is a course a fallacy that resonant antennas
naturally "work better", or that resonance is a necessary condition for
high efficiency.

It is pointed out to me from time to time that the article that I
referred you to earlier is way above the head of the average MFJ259B
user, but it is my contention that you cannot realise much of the
potential of the MFJ259B or the like without understanding transmission
lines. VNAs are the new wave of instruments with potential exceeding
typical user's desire for understanding.

Owen