Ian White GM3SEK wrote:
My point (and Roy's, and Dave's, and that of any textbook author) would
be that there is categorically no way to tell these boxes apart by means
of a steady-state impedance measurement at 4MHz.

Better yet, you can increase the ignorance level even farther
by prohibiting anyone from applying a signal. Then even empty
black boxes cannot be distinguished.

The fundamental point is that impedances of the same value can always be
substituted for one another, and at a given frequency there is no
steady-state measurement that distinguish between them. That
substitution principle is what allows us to use a dummy load to make
tests on a transmitter, and it forms the basis for impedance bridges and
most other forms of impedance measurement.

Methinks a field strength meter will distinguish between
a dummy load and an antenna. :-)
--
73, Cecil http://www.w5dxp.com