Thanks for the comments. Once again, I scanned a posting too hastily,
and somehow missed the "transmitter" part. My comments were appropriate
for a receiving antenna, not transmitting. So let me try to answer both
Tom's and Mark's postings more appropriately.

None of us has a constant current source with which to drive an antenna,
but generally a source with a fixed amount of power and a finite source
impedance. If we did have a constant current source, then yes, adding
more and more ferrite cores would result in more and more power being
delivered by the source, a larger and larger fraction of which would be
dissipated in the ferrite. A 1 megohm resistor would get a bundle of
power from our source, and a 10 megohm resistor would get 10 times as much.

If we have a tuner, we can adjust our source impedance over some range.
Provided that the feedpoint impedance is within that range with the
ferrites in place, we can deliver all our power to the ferrite-antenna
combination. I believe that the fraction of the power applied to the
antenna which ends up in the ferrites monotonically increases as we add
ferrites (assuming we don't move the previously added ones). If the
ferrites were all at the base, the equivalent load circuit would be just
two impedances in series -- the ferrite impedance and the antenna
feedpoint impedance, and it would behave as Tom said. But putting the
ferrite cores anywhere but the base changes the antenna current
distribution, which has a potentially complex effect on the feedpoint
impedance other than just adding the transformed impedance of the core.
This means that not only does Tom's Z3 increase as we add ferrites, but
Z1 changes also.

Roy Lewallen, W7EL

K7ITM wrote:
On Oct 16, 3:40 pm, Roy Lewallen wrote:
...
Regarding the ferrite absorbing energy from the antenna -- the amount
absorbed will be maximum when the ferrite's impedance is the complex
conjugate of the antenna's. For example, if the vertical is resonant and
grounded with no feed system, you'll get maximum ferrite heating when
the ferrite's impedance is around 36 + j0 ohms. If you add more ferrite,
the amount of power absorbed from a passing wave and delivered to the
ferrite will decrease, approaching zero as the ferrite impedance
increases to a large value.
...

I'm puzzling over this, Roy. It seems like this assumes some source
impedance driving the antenna, but maybe I'm missing something in your
analysis.

My thought-process is to treat the antenna as an impedance Z1, the
ferrite an impedance Z2, and the source an impedance Z3, the three of
them being in series. I suppose thinking of the antenna as a constant
impedance as you change its environment with ferrite might not be
quite right, but to the degree that approximation is correct, then I'd
expect maximum ferrite dissipation (absorption) would occur when its
impedance, Z2 is equal to the complex conjugate of (Z1+Z3). On the
other hand, if I feed the antenna with a constant current source, the
ferrite dissipation increases indefinitely as the resistive component
of its impedance increases.

Am I missing something?

Cheers,
Tom