wrote:


Roy Lewallen wrote:

That this concept
is wrong can and has been shown by theory, modeling, and measurement. I
made and posted measurements on this newsgroup in November 2003 which
demonstrated clearly that the presumption is false.


Mike Coslo wrote:

Okay. It looks like we have at least some measurements that differ. Any
idea why that would be?


Yes, because the physical construction of the coil and the antenna
changes the capacitance from the inductor to the outside world and the
impedance loading the coil. It is the ratio of capaciatnce of the coil
to the outside world to the load impedance presented by the whip above
the coil that causes or allows any phase difference in current or
current level at each end of the coil.

It isn't standing waves, it is missing electrical degrees.

I can take a resonant mobile antenna of basically the same height and
construction, change only the coil while maintaining resonance, and
have difference of current and phase of current change all over the
place.

Try reading:

http://www.w8ji.com/mobile_and_loaded_antenna.htm

there is a link to actual measurements in that text.



The loading coil isn't making the antenna act like a physically longer
antenna. In the extreme case of a physically short inductor at the
feedpoint, it's simply modifying the feedpoint impedance and has no
effect whatever on the antenna's radiation.

Would the inductor then be best right past the feedpoint? Certainly
having the inductor at the far end, or in the middle seems like a bad
place for it. (not talking about trap antennas)


No. The current in the antenna below the loading coil (or a top hat of
sufficent capacitance)is essentially uniform. This increases radiation
resistance. Increased radiation resistance can increase efficiency.

See:

http://www.w8ji.com/radiation_resistance.htm

Wow, good pages, Tom.

Okay now. Your results are pretty compelling, and thanks for the
understandable treatment too. I note differing measurements, and a
reason for those measurements I'm still reading the pages, but wanted to
respond before you thought I was ignoring you.

For the next question, which is directed toward Yuri and/or Cecil, is
are your measurements at all related to what Tom reports? Do the numbers
correlate?


- 73 de Mike KB3EIA -