Measuring antenna loss: Heat balance?
 

On the surface, the method seems reasonable. However, remember that heat
(which is energy) is removed by three mechanisms: conduction,
convection, and radiation. And the temperature rise depends on the rate
heat is lost through these three. The effectiveness of each mechanism
will be different for each part of the antenna structure. So to
realistically judge the temperature rise due to RF compared to DC, the
two have to be distributing heat to the same parts of the antenna in the
same amounts. This isn't a trivial task, and no care was taken to do so.

An additional problem with the method is that no attempt was apparently
made to actually measure the amount of RF power being applied to the
antenna. So knowing the amount of power required for equal heating would
be insufficient for determining efficiency even if it could be
accurately measured.

That the method fails is demonstrated by the results. The author
concludes that the sample antennas have much higher efficiency than
known and proven physical laws predict and countless measurements have
confirmed. He's proposed "correcting" NEC, which applies known and
proven physical laws, to agree with his "heuristic" measurements based
on poor methodology and no direct measurement of efficiency such as
field strength. This is a common theme of junk science, and firmly
identifies this work as being in that category. A search for flaws in
his measurement methods is much more likely to be fruitful than
searching for fundamental flaws in NEC and current physical laws.

But I'm sure that some of the same folks who swallow homeopathic
remedies and arrange their lives around astrological predictions will
replace their 160 meter towers with tiny wire loops. P.T. Barnum's
famous observation is still true.

Roy Lewallen, W7EL

Measuring antenna loss: Heat balance?
 

Thanks Roy, your observations and Richard's detailed discussion are just what
I was looking for.

I hope you sell a bunch of copies of EZNEC at Dayton this year!

---Joel

Measuring antenna loss: Heat balance?
 

Joel Koltner wrote:
Hi Tim,

"Tim Shoppa" wrote in message
...
On Mar 22, 9:24 pm, "Joel Koltner"
wrote:
I think his method, especially for physically compact antennas and
feed systems which tend to have very low radiation resistance at HF
frequencies, is a great check on theoretical calculations. There has
to be a meeting point between mathematical models/NEC and reality and
he is working at one such point.

Agreed -- the controversy comes into play in that he ends up computing
electrically-small loop antennas as being upwards of 70-90% efficient,
when everyone "knows" that such antennas are typically 10% efficient.
He even goes after Chu/Wheeler/McLean/etc. in suggesting that the
fundamental limits for the Q of an ESA are orders of magnitude off
(slide 47), and that's pretty sacrosanct terriority (see, e.g.,
www.slyusar.kiev.ua/Slyusar_077.pdf -- even the Ruskies buy into the
traditional results :-) ).


One wants to be careful about "Q" and Chu, etc. If you haven't
actually read the paper, you might think that Chu is talking about Q as
in filter bandwidth (e.g. center frequency/3dB bandwidth), but it's not.
It's the ratio of energy stored in the system to that radiated/lost.
For some systems, the two are the same, but not for all.

Measuring antenna loss: Heat balance?
 

Joel Koltner wrote:
Hi Jim,

Thanks for the thoughts; I hadn't thought of many of the additional loss
mechanisms you mention.

"Jim Lux" wrote in message
...
In the subject case here, think of this: say you had a 2cm diameter
copper bar and you run 100 Amps of DC through it. The current is
distributed evenly, as is the power dissipation. Now run 1 MHz RF
through that same bar. The skin depth is about .065 mm, so virtually
ALL the RF current is contained within a layer less than 1/3 mm thick.
That's a very different heat and thermal distribution (sort of like
the difference between putting that thick steak in the 200F oven and
throwing it on the blazing hot grill).

If you're just looking at surface temperature (i.e., with a thermal
camera), will it take more or power at 1MHz to obtain a given surface
temperature increase than at DC?

At DC, since you're heating up the entire bar, and the only way for the
heat to go is up "out" to the surface... I'm thinking... less power is
needed for a given rise?

That would certainly then overestimate antenna efficiency.


And one would need to be careful about when you've reached thermal
equilibrium (if ever)

Measuring antenna loss: Heat balance?
 

"Jim Lux" wrote in message
...
One wants to be careful about "Q" and Chu, etc. If you haven't actually
read the paper, you might think that Chu is talking about Q as in filter
bandwidth (e.g. center frequency/3dB bandwidth), but it's not.

I read it well over a decade ago. I like to think I've learned a fair amount
since then, so I should probably go back and do it again some time...

I had McLean as a professor as an undergraduate -- he was already ruminating
about Chu not having the full story back in the early '90s, several years
prior to his (apparently pretty regularly referenced) paper on the topic on
'96
(http://www.physics.princeton.edu/~mc...44_672_96.pdf).
(He was also a fan of Goubau antennas and wanted me to help him figure out
just how they worked... I never managed to contribute anything of use towards
that end and graduated and moved, but I did visit him a few years later at
which point he told me it'd really been rather more difficult to figure out
then he'd first thought. Harumph! I do think it's cool that it eventually
ended up on a cover of a book:
http://www.amazon.com/Electrically-S.../dp/0471782556 )

It's the ratio of energy stored in the system to that radiated/lost. For
some systems, the two are the same, but not for all.

Something like... it's exactly true of a simple RLC network (2*pi*total stored
energy/energy lost per cycle)... but one can concoct fancy, higher-order
networks where it isn't exactly correct?

---Joel

Measuring antenna loss: Heat balance?
 

Joel Koltner wrote:
"Jim Lux" wrote in message
...
One wants to be careful about "Q" and Chu, etc. If you haven't
actually read the paper, you might think that Chu is talking about Q
as in filter bandwidth (e.g. center frequency/3dB bandwidth), but it's
not.

I read it well over a decade ago. I like to think I've learned a fair
amount since then, so I should probably go back and do it again some
time...

I had McLean as a professor as an undergraduate -- he was already
ruminating about Chu not having the full story back in the early '90s,
several years prior to his (apparently pretty regularly referenced)
paper on the topic on '96
(http://www.physics.princeton.edu/~mc...44_672_96.pdf).
(He was also a fan of Goubau antennas and wanted me to help him figure
out just how they worked... I never managed to contribute anything of
use towards that end and graduated and moved, but I did visit him a few
years later at which point he told me it'd really been rather more
difficult to figure out then he'd first thought. Harumph! I do think
it's cool that it eventually ended up on a cover of a book:
http://www.amazon.com/Electrically-S.../dp/0471782556
)

It's the ratio of energy stored in the system to that radiated/lost.
For some systems, the two are the same, but not for all.

Something like... it's exactly true of a simple RLC network (2*pi*total
stored energy/energy lost per cycle)... but one can concoct fancy,
higher-order networks where it isn't exactly correct?



or, an antenna, for which the approximation of an RLC is only true in a
limited frequency range.

There's a fairly good literature out there about the limitations of Chu
(after all, he was only the first shot, and modeled it as a single
spherical mode). Harrington was the next bite at the apple, and then
there's a whole raft, particularly when you get into superdirective
arrays or antennas/systems which have non-reciprocal devices in them.
R.C. Hansen and McLean (as you note) are others. When you start talking
about antennas directly coupled to active devices, that's another thing..

Consider that the low impedance of a small loop is a good "match" to the
low output impedance of semiconductor devices in RF applications.. Now
you've got a reactive load hooked to a reactive source.

Measuring antenna loss: Heat balance?
 

On 3/23/2010 1:44 PM, Art Unwin wrote:
On Mar 23, 1:10 pm, wrote:
On Mar 23, 1:56 pm, Art wrote:



On Mar 23, 12:13 pm, Tim wrote:

On Mar 22, 9:24 pm, "Joel
wrote:

I know that many people think G3LHZ is a little bit off his rocker, but out of
curiosity... what he suggests on slide 15 hehttp://frrl.files.wordpress.com/2009...ts-of-small-an...
- is that a valid approach to measuring antenna efficiency? -- Use a thermal
camera to note how much an antenna heats up with a given input power, find out
how much DC power it required to heat it to the same temperature (the
antenna's loss), and -- poof! -- antenna efficiency = (input power-loss)/input
power?

What are the significant loss mechanisms that he's not accounting for? (He
claims his matching network isn't getting at all hot.)

With some feedlines and frequencies, feedline radiation can become an
issue. For example, using 4" ladder line at UHF.

I think his method, especially for physically compact antennas and
feed systems which tend to have very low radiation resistance at HF
frequencies, is a great check on theoretical calculations. There has
to be a meeting point between mathematical models/NEC and reality and
he is working at one such point. There are of course other points too
(e.g. near field and far field measurements).

Tim.

I can't see how the external fields come into it! That would
automatically be within the two vectors that supply acceleration, this
would be measure by the skin depth created by the displacement
current. The accelleration of charge is a constant dependent on the
conductor used. Where the particle goes when acceleration stops i.e.
after leaving the boundary is of no consequence.This would be seen in
the oscillation losses of the radiator
in the same way as with a pendulum

If you dont understand external fields then you dont understand
Maxwell's equations at all. Maxwell is all about fields. This pretty
much means you havent had a clue about anything you have ever said
about antennas.

Jimmie

Jimmy
I am referring to the boundary laws which is energy in versus energy
out.
Maxwells laws finish with the completion of acceleration of charge.

Hmmmmmm.

I thought that you claimed Maxwell is STATIC.

How can anything static accelerate something?

Sorry, I should have spelled it "accellerated", which is probably
another new thing you have made up. So if that's what's going on here,
I apollojive.

tom
K0TAR

The boundary laws are covered by this action and reaction per Newton.
The particle that is accellerated is the smallest known with respect
to mass and we know that it is accellerated to the speed of light
which is known for any particular medium.
snip nonsense
/snip nonsense
Art Unwin KB9MZ....xg

Measuring antenna loss: Heat balance?
 

On Mar 23, 1:50*pm, "Joel Koltner"
wrote:
Hi Tim,

"TimShoppa" wrote in message

...
On Mar 22, 9:24 pm, "Joel Koltner"
wrote:

I think his method, especially for physically compact antennas and
feed systems which tend to have very low radiation resistance at HF
frequencies, is a great check on theoretical calculations. There has
to be a meeting point between mathematical models/NEC and reality and
he is working at one such point.

Agreed -- the controversy comes into play in that he ends up computing
electrically-small loop antennas as being upwards of 70-90% efficient, when
everyone "knows" that such antennas are typically 10% efficient. *He even
goes after Chu/Wheeler/McLean/etc. in suggesting that the fundamental limits
for the Q of an ESA are orders of magnitude off (slide 47), and that's pretty
sacrosanct terriority (see, e.g.,www.slyusar.kiev.ua/Slyusar_077.pdf*-- even
the Ruskies buy into the traditional results :-) ).

Hence, while I don't really have the background to know precisely how much of
what Underhill promotes is true or not, it's definitely intriguing to me, and
I'm looking around for various rebuttals by those more skilled in the art than
I am.

One link I found:http://qcwa70.org/truth%20and%20untruth.pdf(but this was
written before the PowerPoint presentation I originally linked to).

I'm pretty sure that it is not so easy to just measure power in, heat
lost, and assume that everything else is being usefully radiated.

I think that after you've modeled and then built an antenna, that heat
loss and temperature measurements are valuable to determine if the
assumptions you put into the NEC model regarding loss etc. are correct
or not, and where you need to improve your model, especially of
materials like dielectrics.

Even the heat loss measurements require some fairly heavy modeling
just to convert the IR camera images to actual watts per square cm.
Think it's purely radiative? Sometimes yeah, but make the wrong
assumption when really it's convective and you can be off by a factor
of ten to thirty.

Tim.

Measuring antenna loss: Heat balance?
 

On Mar 23, 9:35*pm, Tim Shoppa wrote:
On Mar 23, 1:50*pm, "Joel Koltner"
wrote:



Hi Tim,

"TimShoppa" wrote in message

...
On Mar 22, 9:24 pm, "Joel Koltner"
wrote:

I think his method, especially for physically compact antennas and
feed systems which tend to have very low radiation resistance at HF
frequencies, is a great check on theoretical calculations. There has
to be a meeting point between mathematical models/NEC and reality and
he is working at one such point.

Agreed -- the controversy comes into play in that he ends up computing
electrically-small loop antennas as being upwards of 70-90% efficient, when
everyone "knows" that such antennas are typically 10% efficient. *He even
goes after Chu/Wheeler/McLean/etc. in suggesting that the fundamental limits
for the Q of an ESA are orders of magnitude off (slide 47), and that's pretty
sacrosanct terriority (see, e.g.,www.slyusar.kiev.ua/Slyusar_077.pdf*-- even
the Ruskies buy into the traditional results :-) ).

Hence, while I don't really have the background to know precisely how much of
what Underhill promotes is true or not, it's definitely intriguing to me, and
I'm looking around for various rebuttals by those more skilled in the art than
I am.

One link I found:http://qcwa70.org/truth%20and%20untruth.pdf(butthis was
written before the PowerPoint presentation I originally linked to).

I'm pretty sure that it is not so easy to just measure power in, heat
lost, and assume that everything else is being usefully radiated.

I think that after you've modeled and then built an antenna, that heat
loss and temperature measurements are valuable to determine if the
assumptions you put into the NEC model regarding loss etc. are correct
or not, and where you need to improve your model, especially of
materials like dielectrics.

Even the heat loss measurements require some fairly heavy modeling
just to convert the IR camera images to actual watts per square cm.
Think it's purely radiative? Sometimes yeah, but make the wrong
assumption when really it's convective and you can be off by a factor
of ten to thirty.

Tim.

But Tim Maxwells equations are accepted every where and appear to be
valid.
Because of this antenna computer programs are based on these
equations.
Thus when a optimiser is added the program can change the input to one
that satisfies
Maxwells equations. Assuming programers did a good job in focusing on
the Maxwell equations then we are provided with an array that meets
Maxwells equations.
What more can we possibly need other than a program that accounts for
all forces involved for the generation of ALL radiation available for
communication use that can be propagated
If we have a distrust in the programers or in Maxwells laws then one
should ditch the arrays
supplied by an optimiser and find what some refer to as a "new
technology." Until one comes along we first have to delegitemise
Maxwell and we have been unable to do that!
Maxwells equations can be justified via all known laws in physics
including making static laws dynamic. and adhering to the absolute
requirement of equilibrium with respect to physics laws. The main
problem we have is misinterpretations we add by using lumped loads etc
which Maxwell never included same. This also is the case with the yagi
where
Maxwell never supplied anything with respect to planar or even a
stipulation that elements must be straight, parallel, resonant,
etc ,only EQUILIBRIUM. where all data can be placed on one side of an
equal sign and where on the other side MUST equal zero..
So we dance with the one that 'brung' us
Regards
Art

Measuring antenna loss: Heat balance?
 

On Mar 24, 3:32*am, Art Unwin wrote:
On Mar 23, 9:35*pm, Tim Shoppa wrote:



On Mar 23, 1:50*pm, "Joel Koltner"
wrote:

Hi Tim,

"TimShoppa" wrote in message

....
On Mar 22, 9:24 pm, "Joel Koltner"
wrote:

I think his method, especially for physically compact antennas and
feed systems which tend to have very low radiation resistance at HF
frequencies, is a great check on theoretical calculations. There has
to be a meeting point between mathematical models/NEC and reality and
he is working at one such point.

Agreed -- the controversy comes into play in that he ends up computing
electrically-small loop antennas as being upwards of 70-90% efficient, when
everyone "knows" that such antennas are typically 10% efficient. *He even
goes after Chu/Wheeler/McLean/etc. in suggesting that the fundamental limits
for the Q of an ESA are orders of magnitude off (slide 47), and that's pretty
sacrosanct terriority (see, e.g.,www.slyusar.kiev.ua/Slyusar_077.pdf*-- even
the Ruskies buy into the traditional results :-) ).

Hence, while I don't really have the background to know precisely how much of
what Underhill promotes is true or not, it's definitely intriguing to me, and
I'm looking around for various rebuttals by those more skilled in the art than
I am.

One link I found:http://qcwa70.org/truth%20and%20untruth.pdf(butthiswas
written before the PowerPoint presentation I originally linked to).

I'm pretty sure that it is not so easy to just measure power in, heat
lost, and assume that everything else is being usefully radiated.

I think that after you've modeled and then built an antenna, that heat
loss and temperature measurements are valuable to determine if the
assumptions you put into the NEC model regarding loss etc. are correct
or not, and where you need to improve your model, especially of
materials like dielectrics.

Even the heat loss measurements require some fairly heavy modeling
just to convert the IR camera images to actual watts per square cm.
Think it's purely radiative? Sometimes yeah, but make the wrong
assumption when really it's convective and you can be off by a factor
of ten to thirty.

Tim.

But Tim Maxwells equations are accepted every where and appear to be
valid.
Because of this antenna computer programs are based on these
equations.
Thus when a optimiser is added the program can change the input to one
that satisfies
Maxwells equations. Assuming programers did a good job in focusing on
the Maxwell equations then we are provided with an array that meets
Maxwells equations.
What more can we possibly need other than a program that accounts for
all forces involved for the generation of ALL radiation available for
communication use that can be propagated
If we have a distrust in the programers or in Maxwells laws then one
should ditch the arrays
supplied by an optimiser and find what some refer to as a "new
technology." Until one comes along we first have to delegitemise
Maxwell and we have been unable to do that!

up to here this is the most lucid thing i think i have seen art
write... and then he starts going down hill.


Maxwells equations can be justified via all known laws in physics
including making static laws dynamic. and adhering to the absolute
requirement of equilibrium *with respect to physics laws. The main
problem we have is misinterpretations we add by using lumped loads etc
which Maxwell never included same. This also is the case with the yagi
where
Maxwell never supplied anything with respect to planar or even a
stipulation that elements must be straight, parallel, resonant,
etc ,only EQUILIBRIUM. where all data can be placed on one side of an
equal sign and where on the other side MUST equal zero..
So we dance with the one that 'brung' us
Regards
Art

the planar designs are a _result_ of maxwell's equations plus some
basic mechanical engineering considerations. coupling between
parallel wires or tubes is predictable and easily controlled by
adjusting length and spacing, all in accordance with maxwell's
equations, to make a family of easily designed and constructed
antennas. are they the ultimate, no, i quoted you a book probably a
couple years ago where an optimizer was used and came up with planar
elements that were more like a wavelength long but shaped like a cross
section of a bowl. a 3d optimizer can do other things, but then you
loose some of the important characteristics of the Yagi-Uda arrays,
like the control of polarization and ease of construction. and yes,
you can use maxwell's equations to model lumped elements, you just
have to model them on the appropriate scale with a program that
handles very small segments.