On 11/10/2015 2:36 PM, rickman wrote:
On 11/10/2015 12:40 PM, amdx wrote:
When transmitting with a 96%
efficiency, using silver plating will only improve this to 96.2% at
very best. Not really useful and likely not measurable. Better to deal
with the significant losses like the extremely bad connection between
the vacuum variable cap and the loop. Straps???!!! Get real!


Where did you get 96% efficient?

From the site below.
"The efficiency of a magnetic loop antenna is typically calculated as
(Smith, 2006);

efficiency=Rr/(Rr+Rhf2)

Rr=radiation resistance (ohms)

Rhf2=RF losses from combined skin effect and proximity effect (ohms)

This term is not adjusted for the effects of ground or nearby objects."


This builder has a different design.

http://gridtoys.com/glen/loop/loop3.html

You'll enjoy this line on his page.

"*Aluminum works well in magnetic loop antennas. Yes, pure copper is a
little better, but in multiple conductor magnetic loop antennas, there
may be difficulty getting a copper loop to support its own weight.
Structurally, aluminum is a lot better. Just make the conductors bigger."

Mikek

On 11/11/2015 6:59 AM, amdx wrote:
On 11/10/2015 2:36 PM, rickman wrote:
On 11/10/2015 12:40 PM, amdx wrote:
When transmitting with a 96%
efficiency, using silver plating will only improve this to 96.2% at
very best. Not really useful and likely not measurable. Better to deal
with the significant losses like the extremely bad connection between
the vacuum variable cap and the loop. Straps???!!! Get real!


Where did you get 96% efficient?

PFA It is an example of an efficient loop. Work with a less efficient
loop and the sliver still makes only a small difference, less than the
raw 5% difference in conductivity.


From the site below.
"The efficiency of a magnetic loop antenna is typically calculated as
(Smith, 2006);

efficiency=Rr/(Rr+Rhf2)

Rr=radiation resistance (ohms)

Rhf2=RF losses from combined skin effect and proximity effect (ohms)

This term is not adjusted for the effects of ground or nearby objects."

Your point?

BTW, Rhf2 I believe is intended to be the resistive losses after
considering the skin and proximity effects. As you can see, a 5%
difference in Rhf2 will be less than 5% in the efficiency and depending
on the numbers, much less.

If you are working at very low efficiencies, then yes, a 5% difference
in Rhf2 will result in a noticeable difference in efficiency, but this
would be improved much more by using a good design rather than a poor
one. Silver plating a crap antenna will still give you a crap antenna.


This builder has a different design.

http://gridtoys.com/glen/loop/loop3.html

You'll enjoy this line on his page.

"*Aluminum works well in magnetic loop antennas. Yes, pure copper is a
little better, but in multiple conductor magnetic loop antennas, there
may be difficulty getting a copper loop to support its own weight.
Structurally, aluminum is a lot better. Just make the conductors bigger."

Not sure what he is talking about. He seems to have screwed up the
formulas calcuating the skin effect. I can't reconcile his math.

--

Rick

You analysis of the accordion roughness' effect is relative to the wavelength. I have no idea of the relationship, but my brother whom has designed antenna systems for military aircraft and patented antenna designs schooled on the fact that the formulas we all love and use are WRONG!

However, the formulas we use work well because we typically use relatively thin radiating elements compared to the wavelength, often significantly less than 1% of the operating frequency. The correct formula is surface area of the radiating element NOT LENGTH.

To you and I building wire, Yagi, and loop antenna with skinny radiating elements length ends up being very close to the surface area. However, design an antenna for a cellphone from a thin plate or part of an aircraft fuselage and the length formula starts falling apart, especially at the higher frequencies.

I didn't bother learning the correct formula as it is a little more complex.. I think it may come up when you start building fractal shaped antennas, such as were used in WWII by underground operatives using the lead frames stained glass windows in churches as radiating elements. The surface area formula may become relavent to magnetic loops with radiating loops with very thick radiators.

N4VEP