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

The link should be:
http://www.ece.msstate.edu/~donohoe/ece4990notes5.pdf

Wim
PA3DJS
www.tetech.nl

On 2/28/2011 1:53 PM, Richard Clark wrote:
On Sun, 27 Feb 2011 23:14:34 -0600, John -
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


I didn't mean Wimpie was right about his technical response. I meant he
was right about a part of his message which you cut:

"I agree with you that several statements on Norbert's site will not
hold when scientifically reviewed. However I think the way you
respond will likely not result in better statements."

"As the name of the newsgroup indicates; this is a radio amateur group
and Norbert site starts with "Dutch amateur radio station". This may
require another approach then you should use in a professional
environment. If you prefer that, Edaboard.com (just an example) is a
more suitable place."

John

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,

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

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

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%."

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


Wim
PA3DJS
www.tetech.nl
Don't forget to remove abc in case of PM.

On Mon, 28 Feb 2011 15:36:27 -0600, John - KD5YI
wrote:

I didn't mean Wimpie was right about his technical response. I meant he
was right about a part of his message which you cut:

I selectively quote to make the response specific to the point being
responded to (like I am right now). It saves room, is not ambiguous,
and serves the technical community by confining discussion to
technical matters.

73's
Richard Clark, KB7QHC

This has been a good thread, I have little room for an antenna, a mag loop may be just the ticket for my small Tampa QTH ?

On 2/28/2011 7:24 PM, Richard Clark wrote:
On Mon, 28 Feb 2011 15:36:27 -0600, John -
wrote:

I didn't mean Wimpie was right about his technical response. I meant he
was right about a part of his message which you cut:

I selectively quote to make the response specific to the point being
responded to (like I am right now). It saves room, is not ambiguous,
and serves the technical community by confining discussion to
technical matters.

73's
Richard Clark, KB7QHC

Then I'll just have to put the "point" back in

Quote Wim
I agree with you that several statements on Norbert's site will not
hold when scientifically reviewed. However I think the way you
respond will likely not result in better statements.

As the name of the newsgroup indicates; this is a radio amateur group
and Norbert site starts with "Dutch amateur radio station". This may
require another approach then you should use in a professional
environment. If you prefer that, Edaboard.com (just an example) is a
more suitable place.
/Quote

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

On Tue, 1 Mar 2011 02:25:00 +0000, ka7niq
wrote:

This has been a good thread, I have little room for an antenna, a mag
loop may be just the ticket for my small Tampa QTH ?

Hi OM,

Well, as you can imagine (barring the numerous errors and moral
judgments), it all depends upon the band you want to operate - with
the 40M and higher frequencies quite well served.

A lot of myth surrounds what are called "magnetic loops" and this
thread has corralled some of them - including from Norbert as his page
which forces the argument that fairly agrees that below 40M
performance dives. However, through sloppy bookkeeping, the Ciro
Mazzoni line is not one I would walk away from for stated
"inefficiencies."

The principle consideration is the ratio between radiation resistance
(power that is expressed into making contacts) and Ohmic loss (bulk
metal conductivity power that is expressed into making heat). Wimpie's
choice of 20mm diameter stock (how that arrived in the mix is a
mystery) compares poorly with the Ciro Mazzoni 50mm tubing for its
smallest design.

The 80M design from the vendor uses 75mm stock for good reason and
this should be a selection guide for your application. Their second
80M design uses 140mm stock! Pushing this further with conductance
now nailed down, you want a large loop because the radiation
resistance varies by the fourth power of dimension. That is to say,
if you double the loop radius, you obtain 16 times the radiation
resistance. Small changes in loop radius can quickly escalate or
emasculate efficiency. Radiation resistance is the beneficial
characteristic of how we manage to couple a signal out into space and
which is typically thought of as being 50 Ohms (although this is
rarely the actual value that more often varies between 35 and 70 Ohms
for simple wire antennas of conventional length).

As you can see from these resistance figures, the difference between a
radiation resistance in the thousandths of an Ohm, and typical values
in the tens of Ohms is a hallmark for caution. When paired with metal
resistance in the Ohms (something that ordinarily only comes with
using wire-wrap wire for long runs), you want to boost radiation
resistance as high as possible. When paired with metal resistance
that is in the thousandths of Ohms, there is every chance you are
looking at 50% efficiency for 1 meter diameter loops.

Bigger radius comes with its own problem, however. It limits the high
band of operation as these designs are optimized for being a small
portion of wavelength. Observe the various design options from Ciro
Mazzoni, and you will observe they are specified over only two octaves
for any particular design. That should give you a clue if you want to
homebrew your own, because you will encounter the same limitations of
coverage regardless of construction method.

So, this returns us to the first statement above: it all depends on
which band(s) you want to work. It further depends upon your pain
threshold for poor efficiency if you choose to push beyond the
coverage limits. Professionals describe this in terms of a
cost/benefit ratio. If we restrict discussion to non-professional
qualitative expressions of benefit: super, great, fantastic, maximum
and peg escalating dollar amounts to each with corresponding
breathless emphasis - then there are many deals for sale on those
terms for the gullible.

73's
Richard Clark, KB7QHC

On 1 mar, 03:25, ka7niq wrote:
'Wimpie[_2_ Wrote:



;734551']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,

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

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

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%."

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

Wim
PA3DJS
www.tetech.nl
Don't forget to remove abc in case of PM.

This has been a good thread, I have little room for an antenna, a mag
loop may be just the ticket for my small Tampa QTH ?

--
ka7niq

Hello Chris,

Which antenna will fit your needs depends on many factors (tuning
range, indoor/outdoor, aesthetics, local regulations, your experience/
preference, available volume, house construction, buy or homebrew,
available materials, local or DX use, etc). So I can't judge whether a
loop is good solution in your situation.

In addition, "the" best antenna for the transmitting case will very
likely not be the best one for the reception case.

Best regards,


Wim
PA3DJS
www.tetech.nl