Cecil Moore wrote:
Ian White GM3SEK wrote:
Cecil Moore wrote:
I'm not reclassifying anything. The differences between traveling-wave
antennas and standing-wave antennas have been known for many decades.
Oh good! Exactly where do *you* draw the line between them; and why?
Please justify this by giving examples of two antennas that are very
close to your chosen line, but on opposite sides.

Glad to oblige. The two classical examples are a 1/2WL dipole
vs a terminated rhombic. The differences are obvious. The ends
of the standing-wave 1/2WL dipole are open-circuited so forward
waves undergo a total reflection. Ideally, the traveling-wave
rhombic is terminated in its characteristic impedance so
reflections are eliminated.

The equation for the current in a 1/2WL dipole is roughly
proportional to cos(x)*cos(wt). The equation for the current in
an ideal rhombic is proportional to cos(x+wt) where w=2*Pi*F.
For anyone with a math background, those differences are more
than obvious and I pointed that out years ago.


Thank you; it's useful to clarify from time to time what you do mean,
because many of these disputes are because people are using the same
terms with different meanings.

Then please justify the difference between your two different
classifications of current.

I don't have to justify that, Ian. Mathematics automatically
justifies it for me. If you would simply take the time to understand
the difference between cos(x)*cos(wt) and cos(x+wt), you would
understand it also.

The current in an ideal rhombic is 100% forward current proportional
to cos(x+wt). The current in a 1/2WL dipole is the sum of two
currents. The forward current is roughly proportional to cos(x+wt)
just as it is in the rhombic. The reflected current is roughly
proportional to cos(x-wt) and when those two traveling-wave currents
are added the resultant standing-wave current is proportional to
cos(x)*cos(wt), a completely different kind of current as is obvious
from their different equations.

The mathematics is clear enough, but it provides no justification
whatever for your conceptual leap to "a completely different KIND of
current" (my emphasis). You are only doing that to justify the different
kind of behavior that your model demands for a loading inductance - in
other words, you are trying to patch one error by adding a second error.

I suspect (although it's difficult to separate from the other known
errors) that you are also hopping between two different definitions of
"phase", one for each case, without noticing that you are doing do.

If instead you were to accept that current is simply the net movement of
electrons, and inductance always responds to that in a consistent way,
you would find the whole topic much simpler than you make it out to be.

The Boyer paper that I referenced yesterday shows exactly how the model
of an antenna as a reflective unterminated transmission-line handles
inductive loading.


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek