David Shrader wrote:
wrote:

SNIPPED



If I have a 10 degree tall base loaded antenna it is a ten degree tall
antenna. It is NOT 90 degree resonant antenna with "80 degrees of
missing length" in the inductor, nor with that 80 degree long inductor
behave like 80 degrees of antenna length would.

If I have a 15 degree long physical antenna, center loaded at 10
degrees, with 5 degrees above the coil I do have a 15 degree physical
antenna. That does not mean the antenna is NOT 90 degrees elctrically
long!

If the antenna is 15 degrees long, it is 15 degrees long. I'm not even
sure "90 degree resonant" is a viable phrase, or what it means.

Can I have a series tuned circuit that is "90 degree resonant"? Is the
radiation resistance the same as a 90 degree tall Marconi? Is the
current distribution the same?

If we go to twice the antenna's frequency is it 180 degree resonant?
Does it have a current maximum in the center and HV at each end?

This is as bad as the MFJ 20 foot tall vertical half-wave that covers
80 through 2 meters.


Resonance requires that the reactive components cancel both in
amplitude and phase! Each reactive component introduces phase shift into
the system. The antenna, without a loading coil, is composed of three
terms: resistance [radiation and loss], self capacitance, and self
inductance. In a shortened antenna the self capacitance dominates and
the resultant phase shift is NOT zero. It is required to add inductance
to achieve resonance [phase shift = 0]. If an antenna is electrically 15
degrees long and the self inducance does not reduce the reactive phase
shift to zero PHASE SHIFT MUST BE ADDED TO THE ANTENNA for resonance.
This phase shift is accomplished by the loading coil.

So what? No one disagrees with that. The series loading inductor
corrects power factor, or brings voltage back in pahse with current.
Nothing I've written or read disagrees with that.

Now, when that antenna is fed with 1 ampere [Imax] at the base of the
antenna and the feed current follows a cosine distribution to the base
of the coil [I = Imax*cos(theta)][theta=10], you claim that the current
exiting the coil is also Imax*cos(theta), or 98.5% of max value.

However, if we start with zero current at the tip, a valid initial
condition, and let current increase by a sine function then I =
Imax*sin(theta1][theta1 = 5 degrees] The result is simply 9% of max
value. There seems to be a disconnect here. 98.5% = 9% ?????????

That's because you have failed to realize the antenna has a triangular
distrubution ABOVE the coil. I suggest you look at this link:

http://www.w8ji.com/Topload_Rad_res.bmp


If I understand you correctly, then the measured value at the base of
the 15 degree antenna is NOT 1 ampere but only 0.07 amperes.

Your misunderstanding appears to be rooted in thinking the antenna
above the loading reactor has a sine distribution. It does not. It is
basically triangular.

Unless distribution is correctly visualized, conclusions will be
flawed.

It take a certain number of ampere-feet to radiate a given amount of
power as EM radiation. When the spatial distance of the radiating
element is reduced, the current has to increase. This is just another
way of saying radiation resistance decreases, and current increases.


Therefore, I offer that the loading coil provides the
required additional inductance for resonance.

I'll agree with that. It corrects power factor. It forms a series
resonant circuit with the capacitance presented by the antenna above
the inductor.

The only thing you are missing is the current curves are nowhere like
you assume in the whip above the coil. It's very well documented in
hundreds of peer reviewed engineering texts that current takes on a
triangular distribution in a very short radiator, and that the
intetgrated current over the length of that radiator for a given
radiated power always equals the same ampere-feet.

73 Tom