On 28 feb, 20:53, Richard Clark wrote:
On Sun, 27 Feb 2011 23:14:34 -0600, John - KD5YI
wrote:

Wimpie is right, Richard.

I presume Wimpie can speak for himself. *As he offered musings that
were done on the back of a handy envelope, there is every chance he is
not right. *I offered a similar chance that I was not right either,
but I offered complete (two in fact) equations that no one has
disputed, and none have faulted for computation. *I admitted a
misapplication of one - which also passed without comment.

Considering Wimpie's work was not done for the antenna under
consideration (the size of his being much smaller where radiation
resistance varies by the FOURTH POWER of size) - what does "right"
mean?

73's
Richard Clark, KB7QHC

Hello Richard,

Your formulas can be disputed:

When using (from http://www.ece.msstate.edu/~donohoe/ece4990notes5.pdf):

Rr_loop = 320*(pi)^4*A^2/lambda^4

for f = 3.6 MHz, Dloop = 1.27m (so A = 1.27 m^2),

Rr_loop = 0.001 mOhm.

This result agrees the number in my previous calculation (for the same
situation).

From the same source, but for a dipole of 1.27m with large end-
plates,

Rr_dipole = 80*(pi)^2*le^2/lambda^2 = 0.18
Rr_dipole = 0.045 Ohm (without large end-plates).

This is roughly a factor 45 or 180 more (for the dipole).

Maybe somebody can confirm the above calculations.

The actual efficiency depends on the required (space consuming)
reactive component to cancel the capacitive (dipole) or inductive
(loop) behavior.

The advantage of the loop (especially for reception) is that you need
a variable capacitor instead of a variable loop, and matching / balun
function can be made easily. He also mentioned the vertical radiation
component (NVIS operation) together with the nulls in the horizontal
plane.

Regarding claims, Norbert didn't make claims about the high
efficiency. Please read his conclusion that starts with "despite the
low efficiency of 3%….". His stated 3% reasonably agrees with my 3%
(though you think that the calculation may be wrong). The claim with
regards to performance comparable to a half wave or vertical antenna
is for higher frequencies (where the loop's efficiency increases
significantly).

Of course I have serious doubts about the conclusions regarding
general noise cancelling properties, but the conclusions can be right
for that special RF-environment. Whether they apply for another
situation, can be food for the radio amateur experimenter (or
professional?).


With kind regards,

Wim
PA3DJS
www.tetech.nl