Jeff Liebermann wrote:
On Sat, 11 Oct 2014 11:47:22 -0500, John S
wrote:

Unless I have done something wrong, I see that a dipole that is .05
wavelengths long is within 20% of being as efficient as a half-wave
dipole. Even including wire resistance.

Sounds about right except that it doesn't include any losses
introduced by the necessary matching network and real ground losses at
HF frequencies. Expanding my table to include radiation efficiency:

There is no feed because it is the ANTENNA that is being analyzed, not
an antenna SYSTEM.

And while I don't know if the simulation included it, NEC can include
the ground losses for the ANTENNA.

http://802.11junk.com/jeffl/antennas/Monopole/index.html
Length Gain Radiation
wl dBi Efficiency
0.050 4.75 99.09%
0.125 4.85 99.66%
0.250 5.19 99.93%
0.500 6.96 99.97%
0.625 8.01 99.93%
In other words, there's nothing inherent in the length of the radiator
that would affect radiation efficiency. If there is a drop in
radiation efficiency, then it's mostly due to ground losses, material
losses I2R, and matching losses).

Ground and I^2R losses of the antenna are shown by NEC.

Matching losses are NOT part of the antenna.

I invite discussion in any case.

NEC: Power Efficiency vs. Radiation Efficiency
L. B. Cebik, W4RNL
http://www.antennex.com/w4rnl/col0504/amod75.html
Lots of examples of how "efficiency" calculations work, and how
various common antenna configurations affect the results. (I need to
re-read the article as there's plenty about this which I don't
understand very well). Test cases 5 and 6 are short monopoles, which
should have something to do with short dipoles. From the bottom of
the page:
"Unlike the vertical monopole, the horizontal dipole shows much
more regular changes of radiation efficiency with changes of
soil type, ranging from 80.01% over very good soil to 65.93%
over very poor soil."

Yep, and once the issue of size versus efficieny is put to rest, it would
not be a bad idea to look at the real effects of ground, both in terms
of height in wavelengths and soil quality.



--
Jim Pennino