Hi,

To illustrate technical articles about EM radiations, I' m searching for
thermal images of antennas during transmission ?
Images showing the EM field is welcome too (not radiation pattern but
measured in situ and transposed in false colors)

Any URL to suggest ?

NB. I have well found some thermal images of electronic components but not
of antennas.

Thanks in advance

Thierry, ON4SKY
http://www.astrosurf.com/lombry

Hi,

To illustrate technical articles about EM radiations, I' m searching for
thermal images of antennas during transmission ?

Wow...

That's no longer very common.

Some people have run smaller antennas on thermal paper to map the
currents/voltages.

But a true thermal digital image of an antenna in situ is very difficult,
because of convection currents.

A more common mode is to attach thermal sensors at various points on the
antenna and map the temp as a function of time.

Is that what you had in mind?

73,
Chip N1IR

To illustrate technical articles about EM radiations,
I'm searching for thermal images of antennas during
transmission ?

"Fractenna"
But a true thermal digital image of an antenna in situ
is very difficult, because of convection currents.

Huh? Run some high power into the antenna and click the shutter button. What
could be simpler (assuming you have the right camera). Obviously need a fair
amount of power.

Could model it by simply looking at the current distribution in NEC (current
equals heat, neglecting many other factors).

Comnection currents ?? rolls eyes Okay, run the experiment in a vacuum
chamber smirk.

A more common mode is to attach thermal sensors
[WITH LONGER DANGLING WIRES???] at
various points on the antenna and map the temp
as a function of time.

Bull feathers. The leads would *obviously* (duh!!) screw-up the operation of
the antenna (unless you're proposing fibre optic temp sensors).



BTW - (giving you the opportunity to change the subject and not answer the
questions as per your normal MO thereby maintaining your extreme pompous to
idiocy ratio), did we ever sort out who really invented or developed or
suggested or discovered radiocarbon dating???????

Huh? Run some high power into the antenna and click the shutter button. What
could be simpler (assuming you have the right camera). Obviously need a fair
amount of power.

Thermal images register differentials in temperature . The lower horizon and
ground are usually between 200-300 degrees Kelvin (with no water vapor, the
horizon looks much colder) and it is thus an issue of looking at temperature
changes that are typically a few degrees or less.

Antennas have surface areas and thus heating and cooling rates. The
instantaneous thermal temperature is indicative of the point where these rates
come into equilibrium.

The cooling rate will be affected by the surface layer of air. Usually,
convective cooling is a big factor and biases the true temperature at the
surface. Thus the actual temperature in air is different from that in a vacuum.
I don't believe you are referring to a vacuum.

Electrical thermal probes can and are used.In order to have minimal effects on
the current of the antenna, they are attached by a small but highly heat
conductive paste--an electric insulator as well-- and then choked. Usually the
leads are run normal to the radiator surface.

The amount of power you need is indeed, not small. Fairly large metal surfaces
dissipate heat moderately well through radiation and air convection, so you
could be burning up a fair amount of power and not be able to detect it with
any great precision. If the heated surface is small, i'ts much easier. Most
antennas of interest do not have small surfaces or lengths.

Hope this helps.

73,
Chip N1IR

Bull feathers. The leads would *obviously* (duh!!) screw-up the operation of
the antenna (unless you're proposing fibre optic temp sensors).

Actually, the real problem is that the RF can screw up the very sensitive
probe.

The trick is to do on-offs of antenna power, and register the temperature on
the offs. The duty cycle must be adjusted so that the equilibrium temperature
is being sampled properly. Most of the time, the temp drops noticeably after 30
seconds to a minute. In some cases, the probe can be quickly attached and then
detached during the off cycle.

It's fun to do. Som experimenting shows how to mitigate 'to measure is to
disturb' issues.

Best,
Chip N1IR

"Fractenna"
Thermal images register differentials in temperature.
The lower horizon and ground are usually between
200-300 degrees Kelvin...

I believe you're about half-way to proving that Thermal Images are
impossible. What next? Santa Claus?

Perhaps the delta between our positions is that if the temperature increases
are not significant, then I'm assuming that the information is not of value
(for the purposes that I'm assuming). In other words, a flame test without
the flame. Perhaps you're assuming another (more academic, less practical)
purpose.

I've seen lots of foolishness in this general field (w.r.t. cell phones,
fake heads and measuring temperatures- pure rubbish and a lack of common
sense). The world would be a better place if they sent most of the
researchers in this field on a one-way trip into outer space. The whole
field seems to be infested with idiots (perhaps too much time experimenting
with cell phones?).

On Sun, 17 Oct 2004 14:27:31 +0200, "Thierry" - wrote:

Images showing the EM field is welcome too (not radiation pattern but
measured in situ and transposed in false colors)

Hi Thierry,

Go to:
http://home.comcast.net/~kb7qhc/ante...elds/index.htm
and select any particular antenna style, observe the "false" color
mapping of near fields, and tell me if this is what you mean.

73's
Richard Clark, KB7QHC

On Sun, 17 Oct 2004 11:57:02 -0300, "You're wrong"
wrote:

The world would be a better place if they sent most of the
researchers in this field on a one-way trip into outer space. The whole
field seems to be infested with idiots (perhaps too much time experimenting
with cell phones?).

If I recall my reading of the "Hitchhiker's Guide to the Universe"
the telephone sanitizers were in the 2nd ship to leave - eh?

73's
Richard Clark, KB7QHC

On Sun, 17 Oct 2004 14:27:31 +0200, "Thierry" - wrote:

|Hi,
|
|To illustrate technical articles about EM radiations, I' m searching for
|thermal images of antennas during transmission ?
|Images showing the EM field is welcome too (not radiation pattern but
|measured in situ and transposed in false colors)
|
|Any URL to suggest ?

Sure just buy a copy of this:

http://www.ansoft.com/products/hf/hfss/

I believe you're about half-way to proving that Thermal Images are
impossible. What next? Santa Claus?


It has already been proven that Santa Claus is impossible. Too many chimneys to
crawl down (let alone up: Claus is morbidy obses as I recall)) in one night...


Perhaps the delta between our positions is that if the temperature increases
are not significant, then I'm assuming that the information is not of value

You miss the important issue. Heat is not dissipated at a point but over a
surface. If I take a soldering iron, for example, and distribute its 40 watts
of heat across a strip of 2 feet by 4 inches, for example, it won't get very
warm in a differential way to ambient.

That re-distribution of heat across a larger surface area is how heat sinks
work.

Ergo, the increase in --temperature-- at a point of measurement--or even across
an area or region-- can be small, even though the total amount of ohmic loss
may be high.

Thermal cameras register differential thermal radiation losses, not convective
losses (per se). And the heat is distributed across a surface, not a point.

You can't take a picture of an antenna outside, and learn much about its ohmic
loss, for example. (Too much convective cooling). Not unless its ohmic loss is
confined to a small area, the air is rarefied and windless, and thus the
temperature differential is a few degrees or more and indicative of bona fide
radiative thermal heating/loss.

Hope you learned something:-)!

Best,
Chip N1IR