Roy

I'm a real slopy builder. So, I do alot of half-assed things. I might
begin with a 100 watt light bulb inside the "icebox" to establish a
referance temperature. maybe even a 50 watt and even a 25 watt. And, if
the antenna could be modeled at some frequency where I could build an ice
box thats sufficiently transparent to RF, like 6 Meters, I'd build a full
size antenna for use as a referance.

I've never done something like this. It just sems very practical, since a
100% efficient antenna wouldnt introduce any heat. But , a 50% efficient
one might produce about the same heat as a 50 watt light bulb.

I'd not declare this "ice box" to be a Lab Standard. But, if there was
need, I'd sure try to evaluate the concept.

When people like you cast doubt on anything I tink up, I begin to doubt
myself.

Jerry



"Roy Lewallen" wrote in message
...
There's a fundamental problem in making a scale model of an antenna to
determine loss -- the wire conductivity has to be scaled with frequency.
Of course, the wire diameter can be changed from the normally scaled
size in order to create the same loss, but then the antenna might behave
differently.

It's not clear to me how you could get quantitative data from
measurements in a styrofoam container. Let's say you put 100 watts into
the antenna for five minutes and the temperature rise (of the coil?
helical winding? air?) was 10 degrees C. How would you calculate the
loss or efficiency from that information?

Roy Lewallen, W7EL

Jerry Martes wrote:

Youve gotten too refined. I mostly know about basic antenna theory
and
modeling. But building a VHF model of a 40 meter antenna with #12
copper
wire wound around a 4 inch mandril might be impractical.
But, if the "wonder antenna" is small enough to be enclosed (mostly)
in
something transparent to the RF but not to the thermal thats generated
by
any I^2* R losses, wouldnt the temperture rise inside the enclosure give
a
decent indication of efficiency?

If this "wonder antenna" designer claims to be able to shape the
radiation
pattern with an antenna significantly shorter that a 1/4 wave stub, He
really has something. I suspect that the something he has is mental
illness.

I've been following this info on the RI antenna and have considered it
to
be so 'snake oilish' that it would never see the light of an auditorium.

Your post about attending the lecture made me wonder if anyone asked
about
*any* simple (approximations) measurements like the styrofoam radome to
get
some idea of the I^2*R power lost in the antenna. If he has an antenna,
and
a transmitter and enough room to build a foam igloo it seems that alot
of
data on efficiency could be obtained.
If I had any interest in describing an antenna I'd built, I'd at least
use
an infared thermometer on the section of the antenna suspected as being
the
most lossy.

Jerry

Jerry Martes wrote:

Roy

I'm a real slopy builder. So, I do alot of half-assed things. I might
begin with a 100 watt light bulb inside the "icebox" to establish a
referance temperature. maybe even a 50 watt and even a 25 watt. And, if
the antenna could be modeled at some frequency where I could build an ice
box thats sufficiently transparent to RF, like 6 Meters, I'd build a full
size antenna for use as a referance.

I've never done something like this. It just sems very practical, since a
100% efficient antenna wouldnt introduce any heat. But , a 50% efficient
one might produce about the same heat as a 50 watt light bulb.

It would if the thermal mass of the antenna were the same as the light
bulb, and if the thermal loss through the wiring were the same for the
antenna as for the light bulb. But otherwise, they could be vastly
different.

I'd not declare this "ice box" to be a Lab Standard. But, if there was
need, I'd sure try to evaluate the concept.

When people like you cast doubt on anything I tink up, I begin to doubt
myself.

Jerry

Well, then I've done a good service. Only when you have doubts about
your methodolgy will you have any incentive to take the time to try and
understand what you're doing.

Any conclusions you reach about the antenna's efficiency (except that
it's not 100% efficient - duh) will be completely worthless unless you
get at least some kind of handle on the relationship between the heat
and the temperature.

Roy Lewallen, W7EL

"Roy Lewallen" wrote in message
...
Jerry Martes wrote:

Roy

I'm a real slopy builder. So, I do alot of half-assed things. I
might
begin with a 100 watt light bulb inside the "icebox" to establish a
referance temperature. maybe even a 50 watt and even a 25 watt. And,
if
the antenna could be modeled at some frequency where I could build an
ice
box thats sufficiently transparent to RF, like 6 Meters, I'd build a
full
size antenna for use as a referance.

I've never done something like this. It just sems very practical,
since a
100% efficient antenna wouldnt introduce any heat. But , a 50%
efficient
one might produce about the same heat as a 50 watt light bulb.

It would if the thermal mass of the antenna were the same as the light
bulb, and if the thermal loss through the wiring were the same for the
antenna as for the light bulb. But otherwise, they could be vastly
different.

I'd not declare this "ice box" to be a Lab Standard. But, if there
was
need, I'd sure try to evaluate the concept.

When people like you cast doubt on anything I tink up, I begin to
doubt
myself.

Jerry

Well, then I've done a good service. Only when you have doubts about
your methodolgy will you have any incentive to take the time to try and
understand what you're doing.

Any conclusions you reach about the antenna's efficiency (except that
it's not 100% efficient - duh) will be completely worthless unless you
get at least some kind of handle on the relationship between the heat
and the temperature.

Roy Lewallen, W7EL

Roy

Since I consider antenna efficiency difficult to measure accurately, I'd
be willing to try to measure it as carefully as *practical*. If that
required that the referance heater had a similar "thermal mass" to that of
the antenna under test, I could probably make a heater that did have a
thermal mass equivalent to that of the antenna.
But, I would propose that there is no easier way to actually measure an
antenna's efficiency than to measure the amount of power it turns into heat.
Thats a statement I cant back up, and I know it.

What is a better way to measure an antenna's efficiency??

Jerry Martes wrote:
Roy

Since I consider antenna efficiency difficult to measure accurately, I'd
be willing to try to measure it as carefully as *practical*. If that
required that the referance heater had a similar "thermal mass" to that of
the antenna under test, I could probably make a heater that did have a
thermal mass equivalent to that of the antenna.
But, I would propose that there is no easier way to actually measure an
antenna's efficiency than to measure the amount of power it turns into heat.
Thats a statement I cant back up, and I know it.

What is a better way to measure an antenna's efficiency??


I believe it would usually be easier and more accurate to measure the
amount of power it turns into radiation. That is, measure the strength
of the radiated field compared with an antenna of known efficiency and
preferably having a similar pattern.

Neither is easy, and a method that's "practical" from your point of view
might well yield results which are so grossly inaccurate as to be
useless. But go ahead, do a careful estimate of the accuracy you expect,
do some measurements of various simple antennas whose loss is easy to
calculate and compare the measured results, and see how well you can do.
It's probably within the reach of a very careful amateur to make
measurements which are accurate enough to be useful. It just isn't easy,
and requires knowing the relationship between heat and temperature,
where the heat is going, sources of error and the amount they can
contribute, and a whole lot of care and attention to detail. And that's
to get even crudely accurate results.

For myself, I'd model it as Reg suggests (although I'd use a program
rather than the back of an envelope as he would) and easily believe that
the model results are more accurate than any measurement I'd be able to
make. However, neither calculation or measurement results are likely to
alter the claims made by manufacturers of miracle antennas and their fans.

Roy Lewallen, W7EL

"Roy Lewallen" wrote in message
...
Jerry Martes wrote:
Roy

Since I consider antenna efficiency difficult to measure accurately,
I'd
be willing to try to measure it as carefully as *practical*. If that
required that the referance heater had a similar "thermal mass" to that
of
the antenna under test, I could probably make a heater that did have a
thermal mass equivalent to that of the antenna.
But, I would propose that there is no easier way to actually measure
an
antenna's efficiency than to measure the amount of power it turns into
heat.
Thats a statement I cant back up, and I know it.

What is a better way to measure an antenna's efficiency??


I believe it would usually be easier and more accurate to measure the
amount of power it turns into radiation. That is, measure the strength
of the radiated field compared with an antenna of known efficiency and
preferably having a similar pattern.

Neither is easy, and a method that's "practical" from your point of view
might well yield results which are so grossly inaccurate as to be
useless. But go ahead, do a careful estimate of the accuracy you expect,
do some measurements of various simple antennas whose loss is easy to
calculate and compare the measured results, and see how well you can do.
It's probably within the reach of a very careful amateur to make
measurements which are accurate enough to be useful. It just isn't easy,
and requires knowing the relationship between heat and temperature,
where the heat is going, sources of error and the amount they can
contribute, and a whole lot of care and attention to detail. And that's
to get even crudely accurate results.

For myself, I'd model it as Reg suggests (although I'd use a program
rather than the back of an envelope as he would) and easily believe that
the model results are more accurate than any measurement I'd be able to
make. However, neither calculation or measurement results are likely to
alter the claims made by manufacturers of miracle antennas and their fans.

Roy Lewallen, W7EL

Roy

If I had your credentials, I'd measure antenna efficiency the way you
prescribe.
It is only because I have no faith in my abiliuty to convince anyone what
the pattern of a "New-Revolutionary is, that I'd get a thermometer out to
chech my predictions that the antenna has *no* loss, like this guy does.

As I read this thread, there is one guy who thinks measuring the
temperature of an antenna for getting information on its efficiency. And
all the other posts consider that guy to be 'on the wrong path'. I'd advise
doing it some way *other than* measuring heat of the antenna.

Jerry

On Mon, 16 Aug 2004 23:25:20 GMT, "Jerry Martes"
wrote:

What is a better way to measure an antenna's efficiency??

Hi Jerry,

I see you are suffering from answers out to three decimals again.

Your idea is not so far fetched, it is the simple calorimetric bomb.
With enough patience and references, yes, you could measure
inefficiency. However, the inefficiency could easily be lost in the
inaccuracy and patience is not a virtue where simpler methods prevail.

You rightly note that a total integration of all field strengths would
be required, and be far more cumbersome. This is the classic
treatment, but when done once with a reference for comparison, it is
unnecessary to apply to other antennas of simple characteristics.
Others note that simple comparisons serve quite suitably. For a small
antenna (that is, in relation to wavelength such as the DLM and others
like CFA/eh/fractals purport to operate efficiently in) there is no
hint that the radiation lobes are going to offer manifestly high gain
so as to drive comparisons off the chart. Certainly inventors make
such fantasy claims, and those claims characteristically remain
unsubstantiated. The DLM is a classic example.

Side by side comparisons of the DLM with known good antennas, or even
known poor ones with similar lobe patters could easily reveal
efficiency. I suppose these same inventors could crow about a razor
thin 24dB gain lobe pointed at the horizon (if you only knew the
tune-up procedures), but you are not going to find this from any
antenna packed into a box with less than quarterwave dimensions on all
sides. [readers: Examples proving this last sentence wrong are
welcome.]

73's
Richard Clark, KB7QHC

The most intelligent, sensible and successful radio engineers make no
attempt to measure antenna radiating efficiency. It never occurs to them to
do so - they invariably calculate it.

It takes no longer than a couple of minutes on the back of a used envelope,
using a pocket calculator. It is more accurate and is absolutely certain to
be enormously less expensive.

But perhaps some old wife who cannot do simple arithmetic will find a fellow
creature somewhere in Google who is reported as having attempted to measure
it.

The real problem lies in the western world's educational system. Arithmetic
has been neglected for far too long. It will take two generations to return
to normal and dis-arm children who take loaded guns, even automatic weapons,
to school. Never mind about tower blocks. As a priority, teachers must be
protected from acts of terrorism.

But too late. Chinese and other Eastern countries' education, science,
engineering and technology will have already acheived supremacy.

But why make a battle out of it? I'm sure the peaceful, generous, Chinese
will be quite willing to share the products of their educational system.
----
Reg, G4FGQ