On Fri, 24 Feb 2006 11:48:22 -0500, Amos Keag
wrote:

Resonance has NOTHING to do with impedance. Resonance is resonance; it
has a harmonic response.

Hi Amos,

Resonance is the absence of reactance, or more properly its term is 0.
As reactance is fully part of the specification to impedance,
resonance has a very unique relation: r ±j0.

You can take a dipole that exhibits this unique characteristic at
regular intervals of frequency - notably at harmonics (in a perfect
world, not so necessarily in life). You can also take that same
length of wire and shift the feedpoint such that its resonance (still
that same characteristic loss of X with some remaining R) changes in
frequency - as does the spectrum of other resonances which are
sometimes no longer related by harmonics.

Taking as an example, an 11 segment 3mm wire 37.9M long in free space
and feed it in the conventional way (in the middle) and its resonances
may be observed at:
3.8 MHz¹
7.95 MHz²
11.75 MHz¹
16.25 MHz²
19.65 MHz¹
24.65 MHz²
27.55 MHz¹

Or feed it at 68% along its length (or segment 8) and observe:
3.8 MHz¹ (with a Higher R as I had incorrectly argued with Dan)
5.65 MHz²
7.85 MHz¹
12.45 MHz²
15.65 MHz¹
17.55 MHz²
19.65 MHz¹
25.55 MHz²
27.55 MHz¹

where strictly speaking MHz¹ is resonance and MHz² is anti-resonance

A curious property has emerged, we now have 9 resonances (speaking
largely) where formerly we had 7 in exactly the same span of frequency
for the same piece of wire. Further, we also have the anti-resonance
of the standard dipole at 8 MHz replaced by a resonance in the OCF
dipole.

To roll back the calendar 10 years or so, this is also the hallmark of
fractal antennas in that they exhibit more resonances than found in
"conventional" dipoles.

There are certain lengths of wire, with certain offsets of feed that
offer fairly good overlaps with Ham Bands that are not otherwise found
in common dipoles. I am at a loss to specify those "certain"
characteristics, and it is arguable that feeding an offset dipole can
be successfully achieved without some effort in isolating (choking)
the feedpoint from the driveline - a distasteful reality conveniently
discarded in modeling.

73's
Richard Clark, KB7QHC