On Mon, 28 Feb 2011 14:13:29 -0800 (PST), Wimpie
wrote:

you used r = 1m (as you have r in your formulas), that is D = 2m,
6.28m circumference.

It is the specified diameter/radius of the 80M antenna at the link of
the antenna manufacturer. I stated that quite clearly. I choose to
go to the source rather than rely on possible transcription errors in
amateur postings.

I used D = 1.27m (4m perimeter), that is r = 0.635 m.

That antenna does not exist.

Quote from Norbert's site:
"When a magnetic loop antenna is used for 3.5 MHz with a perimeter of
4 meter (13.3 foot) , it has an efficiency of approximately 3%."

There is no Ciro Mazzoni antenna with that dimension.

I specifically asked if this statement was for the MIDI loop antenna
with a 2 meter diameter (and is designed for 80M operation). To this
point no one has affirmed or denied this my natural selection from the
manufacturer. The page quite clearly reveals three photos of the
distinctive design. The Mazzoni antennas also come in distinctive 1m,
2m, 4m integral sizes. There is no 1.27m diameter tuned loop
offering.

Maybe this helps you to explain the difference between your and my
result,

The original page (2) contains errors or misattribution (same thing),
that is why I am careful to trim away the textual noise and restate
what I perceive to be the model under investigation.

73's
Richard Clark, KB7QHC