Knowledge of antenna bandwidth is not of great practical use at HF
because
the Q of the feedline plus tuner has at least the same effect on the
overall
system bandwidth as the antenna.

I'm sorry, you lost me there Reg. How does the Q of a modern
broadband amplifier feeding a nom. 75 ohm feedline contribute more to
system Q than an 80 meter 1/2 wave dipole made from 2mm wire -- or for
that matter even one that's a half-meter diameter cage (though by then
it doesn't much matter for ham use)?

Cheers,
Tom
================================
Tom, who said anything about 75-ohm lines? And there's still a tuner, with
FIXED settings, to contend with.

In any case an antenna can present a match to a line at only one frequency
in the band. The transmission line transforms the mismatch at the antenna
to something else at the tuner and something yet again at the transmitter.

Lines and tuners have lots of inductive reactance, lots of capacitative
reactance, but not a lot of resistance. Which are just as much a part of
the system as the antenna, if not the greater part. Q =
reactance/resistance. Bandwidth is proportional to 1/Q

What the transmitter sees, even with a precisely known antenna bandwidth, is
anybody's guess.
----
Reg, G4FGQ