Well Tom, I'm just looking to explain the data: I'm puzzled as well.
Same truck, Durango with a ball mount right rear.
Same MFJ analyzer. Same very short coax from inside the truck.
Everything grounded with 2" copper strap.
Same 14.300 MHz; Same whip. The measurements repeat reliably.
Three motor-tuned antennas, Nott, Tarheel, Hi-Q.
Three different impedances at resonance (ie purely resistive load.)
9, 20 and 30 ohms. Now I can see the radiation resistance being slightly
higher with the Tarheel, it's a foot longer, but that hardly explains a
factor of two. So it must be the loss resistance. Part of the difference is
the base tube, and the copper/aluminum/diameter issue obeys the appropriate
scaling laws. (BTW I think the Hi-Q is 1.5" diameter, but I'm not sure and I
am not at the ranch where the antenna is stored.)
When I adjust the tap on the transformer to give a 50 ohm load to the MFJ
for each antenna, the Nott gives the greatest near-field signal strength.
Perhaps a further investigation of the remaining sources of resistance is in
order. The Hi-Q should have the least leakage, it's a beautiful piece of
work. The Tarheel appears to be built of better materials than the Nott.
(Lexan vs PVC for example.) Go down to 80 meters and they're all 10 ohms;
coil losses clearly dominate there where radiation resistance is tiny.

I think a complete solution to Maxwell's Equations would be helpful, but I'm
busy at the moment.

For all I know the paint or powder coating on the aluminum antennas is the
real culprit.
The Nott's just bare copper.
What is the radiation resistance of an 8 foot whip antenna resonant in a
16.5 foot world?
Just a bit less than 10 ohms, right?
Maybe the comparison should be to BARE aluminum.
Just my morning thought on a puzzle I've been looking at for several months.

73 es tnx fer qso
de nq5h
k


"Tom Bruhns" wrote in message
m...
"H. Adam Stevens, NQ5H" wrote in message
...

The Nott is 2" diameter bare copper 3' long.
The Tarheel is 2" diameter painted aluminum 4' long.
The Hi-Q is 1" diameter powder-coated aluminum 3' long.

A 2" diameter bare copper rod or cylinder at 14MHz, 3' long, should
have an RF resistance about 6 milliohms. The worst aluminum alloy
you're likely to see should be about 12 milliohms; 24 for the 1"
diameter. What am I missing here? How does that translate to a
change from 9 ohms to 20 ohms to 30 ohms at the feedpoint? If the
cause is resistance heating of the copper or aluminum tube, what's
doing the impedance transformation, and how is it so efficient? That
much loss should result in measurable temperature rise in the tube (or
wherever the loss is), at 100-W power levels.

Or perhaps my image of what you're measuring is all out of whack.
Same loading coil in each case? I'd kind of expect the loading coil
to be the main loss mechanism, if all the connections are tight.

Puzzled and seeking enlightenment,
Tom