"Meindert Sprang" wrote
"Jack Painter" wrote in message
news3lvc.5786$Y21.4832@lakeread02...
C'mon ol' salt, you should know the inside of copper pipe is
electrically
identical to both sides of copper strap when a bonding connection is
made
to
either. Skin effect of electrical current is felt equally on both in
_that_
condition.

No it isn't. Consider a massive rod of 1". RF flows at the outside due to
skin effect. No remove the innards of the rod, leaving, say 1/16" of wall.
Why would current suddenly flow at the inner surface? It isn't, for the
same
reason it was on the outside when the rod was massive.

Besides, heavy coils in radio stations are all tubes and cooled by running
water through them. Due to the skinn effect, the water is not 'touched' by
the RF.

Electromagnetic induction on a material from one outside
direction sees skin effect on the outside surface only of a closed
structure, cabinet, pipe, etc. But we are not talking about EMF's.

Yes we are. And EMF is exactly the reason why the electrons start to
repell
eachother. And the only place where they are as far apart as possible is
on
the outside of the tube.

Meindert, water is not a good conductor, with average tap water having
100,000 ohms resistance across 1 meter of 15mm plastic pipe filled with
water. Even at RF frequencies, where skin effect is most pronounced, a
bonded connection made equally to both inside and outside of a copper pipe
should exhibit skin effect throughout most of the entire cross section of
the copper pipe. This is because the wall thickness of the copper pipe is
not materially different from copper strap.

Example:

For copper tubing used as a inductor in antenna tuners:

coil length
R= ---------------------------------------
conductivity *skindepth*2pi*coil radius

Now, applying voltage to the outer surface only of copper tubing with closed
ends, whether by EMF attachment or bonded connection to the outside only,
would exhibit surface-only skin effect similar to if a faraday cage was
constructed of the same copper strap we are talking about. The outside
surface would carry most current. But if the voltage connection was bonded
to both inside and outside of an opening of the faraday box or the copper
tubing, then current via skin effect would be nearly constant on the inside
and outside surfaces of the box, defeating the faraday effect. The
condition I originally described, that of a bonded connection, applies
voltage equally and carries current equally on the entire skin of the
conductor, inside and out, 360 degrees, as efficiently as a piece of copper
strap of similar cross section.

Best regards,

Jack Painter
Virginia Beach, Va

In article Wmnvc.6104$Y21.5577@lakeread02,
"Jack Painter" wrote:

Meindert, water is not a good conductor, with average tap water having
100,000 ohms resistance across 1 meter of 15mm plastic pipe filled with
water. Even at RF frequencies, where skin effect is most pronounced, a
bonded connection made equally to both inside and outside of a copper pipe
should exhibit skin effect throughout most of the entire cross section of
the copper pipe. This is because the wall thickness of the copper pipe is
not materially different from copper strap.

Example:

For copper tubing used as a inductor in antenna tuners:

coil length
R= ---------------------------------------
conductivity *skindepth*2pi*coil radius

Now, applying voltage to the outer surface only of copper tubing with closed
ends, whether by EMF attachment or bonded connection to the outside only,
would exhibit surface-only skin effect similar to if a faraday cage was
constructed of the same copper strap we are talking about. The outside
surface would carry most current. But if the voltage connection was bonded
to both inside and outside of an opening of the faraday box or the copper
tubing, then current via skin effect would be nearly constant on the inside
and outside surfaces of the box, defeating the faraday effect. The
condition I originally described, that of a bonded connection, applies
voltage equally and carries current equally on the entire skin of the
conductor, inside and out, 360 degrees, as efficiently as a piece of copper
strap of similar cross section.

Best regards,

Jack Painter
Virginia Beach, Va

Jeeezzz Louise Jack, where did you learn all this BS that your spreading.

But if the voltage connection was bonded
to both inside and outside of an opening of the faraday box or the copper
tubing, then current via skin effect would be nearly constant on the inside
and outside surfaces of the box, defeating the faraday effect.

Please explain how one "BONDS" a connection to only the inside of a
copper pipe. All of the Physic Professors of the World would really
like to know. Are you saying that if one made a "RF Connection",
to only the inside of a copper tube, that no RF would flow on the
outside of the tube? That is just plain wrong, and a stupid statement
on it's face.

ok, enough of this BS, CFR!!! (Call for Reference) Let's see if old
Jack can actually come up with some documentation that RF flows on the
inside of a connected copper tube or pipe. Lets go for some Peer
Reviewed Documentation here, the straight, No ****, Textbook, kind
of documentation, written by some really Qualified Physics Phd's.

Hmmmm, all the PhdEE's that I asked, just laughed and ask how the
weather and fishing was.........

Bruce in alaska
--
add a 2 before @

"Bruce in Alaska" wrote
"Jack Painter" wrote:

Meindert, water is not a good conductor, with average tap water having
100,000 ohms resistance across 1 meter of 15mm plastic pipe filled with
water. Even at RF frequencies, where skin effect is most pronounced, a
bonded connection made equally to both inside and outside of a copper
pipe
should exhibit skin effect throughout most of the entire cross section
of
the copper pipe. This is because the wall thickness of the copper pipe
is
not materially different from copper strap.

Example:

For copper tubing used as a inductor in antenna tuners:

coil length
R= ---------------------------------------
conductivity *skindepth*2pi*coil radius

Now, applying voltage to the outer surface only of copper tubing with
closed
ends, whether by EMF attachment or bonded connection to the outside
only,
would exhibit surface-only skin effect similar to if a faraday cage was
constructed of the same copper strap we are talking about. The outside
surface would carry most current. But if the voltage connection was
bonded
to both inside and outside of an opening of the faraday box or the
copper
tubing, then current via skin effect would be nearly constant on the
inside
and outside surfaces of the box, defeating the faraday effect. The
condition I originally described, that of a bonded connection, applies
voltage equally and carries current equally on the entire skin of the
conductor, inside and out, 360 degrees, as efficiently as a piece of
copper
strap of similar cross section.

Best regards,

Jack Painter
Virginia Beach, Va

Jeeezzz Louise Jack, where did you learn all this BS that your spreading.

But if the voltage connection was bonded
to both inside and outside of an opening of the faraday box or the
copper
tubing, then current via skin effect would be nearly constant on the
inside
and outside surfaces of the box, defeating the faraday effect.

Please explain how one "BONDS" a connection to only the inside of a
copper pipe. All of the Physic Professors of the World would really
like to know. Are you saying that if one made a "RF Connection",
to only the inside of a copper tube, that no RF would flow on the
outside of the tube? That is just plain wrong, and a stupid statement
on it's face.

ok, enough of this BS, CFR!!! (Call for Reference) Let's see if old
Jack can actually come up with some documentation that RF flows on the
inside of a connected copper tube or pipe. Lets go for some Peer
Reviewed Documentation here, the straight, No ****, Textbook, kind
of documentation, written by some really Qualified Physics Phd's.

Hmmmm, all the PhdEE's that I asked, just laughed and ask how the
weather and fishing was.........

Bruce, you're making a totally off the wall argument now, with opposite
assumptions that were never asserted or offered by any of the posters to
this thread. Taking your questions literally as you phrased them would
generate a laugh by all, indeed. If a laugh was your intention, we'll all
have a good one. But I doubt that you are confused about skin effect, or why
a faraday cage works, and specifically what would defeat it's protection
(ie: an opening). So if you seriously think that for instance, a c-clamp
applied across an open end of thin walled copper tubing, contacting the
inner and outer wall in it's grip, would apply voltage differently to the
inside versus the outside of this tubing, then it will be easy to explain
your error in thinking. And since I did not make a joke of your obvious
geometry and math errors in determining the surface area of an object, one
which you continue to be confused about, I would suggest that we either: end
the thread if you do not desire pleasant and professional discussion, or,
omitting the snide comments that do not reflect well on the group or it's
interested participants.

Respectfully,

Jack Painter
Virginia Beach, Va

On Thu, 3 Jun 2004 14:56:44 -0400, "Jack Painter"
wrote:


Bruce, you're making a totally off the wall argument now, with opposite
assumptions that were never asserted or offered by any of the posters to
this thread. Taking your questions literally as you phrased them would
generate a laugh by all, indeed. If a laugh was your intention, we'll all
have a good one. But I doubt that you are confused about skin effect, or why
a faraday cage works, and specifically what would defeat it's protection
(ie: an opening). So if you seriously think that for instance, a c-clamp
applied across an open end of thin walled copper tubing, contacting the
inner and outer wall in it's grip, would apply voltage differently to the
inside versus the outside of this tubing, then it will be easy to explain
your error in thinking. And since I did not make a joke of your obvious
geometry and math errors in determining the surface area of an object, one
which you continue to be confused about, I would suggest that we either: end
the thread if you do not desire pleasant and professional discussion, or,
omitting the snide comments that do not reflect well on the group or it's
interested participants.

Respectfully,

Jack Painter
Virginia Beach, Va



Oh boy! I just got back from vacation and am just now reading this
stuff.

Jack, Bruce and the others are entirely right. I once had a hard time
figuring out why RF would not flow on the inside of a tube too. It
would seem logical that it would do as you say but it doesn't.

Look up "wave guide beyond cutoff". That will answer your question
about why rf dose not flow on the inside of a tube.

It will flow on the inside for only a very short distance from the
opening. Then it gets canceled. This is how many signal generator
attenuater work.
They use a tube of 6 or so inches long with a sliding probe inside fed
from one end. On the other open end is a fixed pickup probe. When the
movable probe is close to the fixed probe on the other end, maximum
signal coupling is obtained. As the other probe is moved away inside
the tube the signal becomes highly attenuated.

It is operating as a wave guide that is much too small for the
frequency involved. If the tube diameter was made large enough to be a
quarter wave length in diameter then the rf would propagate through
it. But that would be in a different mode than the skin effect
conduction being discussed.

By the way did you know that skin effect even comes into play in 60 hz
distribution systems?

Regards
Gary

"Gary Schafer" wrote

Oh boy! I just got back from vacation and am just now reading this
stuff.

Jack, Bruce and the others are entirely right. I once had a hard time
figuring out why RF would not flow on the inside of a tube too. It
would seem logical that it would do as you say but it doesn't.

Look up "wave guide beyond cutoff". That will answer your question
about why rf dose not flow on the inside of a tube.

It will flow on the inside for only a very short distance from the
opening. Then it gets canceled. This is how many signal generator
attenuater work.
They use a tube of 6 or so inches long with a sliding probe inside fed
from one end. On the other open end is a fixed pickup probe. When the
movable probe is close to the fixed probe on the other end, maximum
signal coupling is obtained. As the other probe is moved away inside
the tube the signal becomes highly attenuated.

It is operating as a wave guide that is much too small for the
frequency involved. If the tube diameter was made large enough to be a
quarter wave length in diameter then the rf would propagate through
it. But that would be in a different mode than the skin effect
conduction being discussed.

By the way did you know that skin effect even comes into play in 60 hz
distribution systems?

Regards
Gary

Hi Gary, welcome back, and thanks for your replies.

Right principles, wrong application. Trying to apply high power microwave
principles (3-15 gHz) to low power 2-30 mHz) is not the same. Now at 100 mHz
and below, while there would still a small but measurable difference of skin
effect at high transmit power, it ain't much and has nothing to do with low
power 2-30 mHz where a thin walled copper tube has ZERO measurable
difference in skin effect to a copper strap of even slightly smaller gage.
That has been my never paid attention to point all along, that skin effect
involves the entire cross section of thin material, and copper tubing is
more than thin enough to carry current in it's entire (that means from outer
to inner surface) cross section. That's exactly why copper tube is used so
much in AM broadcast components. This is not even related to waveguides
which must by design AVOID all skin effect which causes great resistance and
heating at the current and velocites involved in microwave transmission.

As we eventually got around to research rather than blindly arguing
positions of opinion, then the participants hopefully learned something.
I've learned that applying the math from formulas for skin effect in
conductors of known ohmic value and used with a known frequency can
determine the wall thickness of a conductor which has full cross sectional
current on it. Guess what? The original poster's question about using copper
tubing remains answered. A 1" copper tube has more surface area and carries
just as much low power RF on it's entire cross section as a 1" wide piece of
copper strap that is nearly the same gage.

Best,

Jack Painter
Virginia Beach Va

On Tue, 8 Jun 2004 17:05:53 -0400, "Jack Painter"
wrote:

"Gary Schafer" wrote

Oh boy! I just got back from vacation and am just now reading this
stuff.

Jack, Bruce and the others are entirely right. I once had a hard time
figuring out why RF would not flow on the inside of a tube too. It
would seem logical that it would do as you say but it doesn't.

Look up "wave guide beyond cutoff". That will answer your question
about why rf dose not flow on the inside of a tube.

It will flow on the inside for only a very short distance from the
opening. Then it gets canceled. This is how many signal generator
attenuater work.
They use a tube of 6 or so inches long with a sliding probe inside fed
from one end. On the other open end is a fixed pickup probe. When the
movable probe is close to the fixed probe on the other end, maximum
signal coupling is obtained. As the other probe is moved away inside
the tube the signal becomes highly attenuated.

It is operating as a wave guide that is much too small for the
frequency involved. If the tube diameter was made large enough to be a
quarter wave length in diameter then the rf would propagate through
it. But that would be in a different mode than the skin effect
conduction being discussed.

By the way did you know that skin effect even comes into play in 60 hz
distribution systems?

Regards
Gary

Hi Gary, welcome back, and thanks for your replies.

Right principles, wrong application. Trying to apply high power microwave
principles (3-15 gHz) to low power 2-30 mHz) is not the same.

Sorry Jack but you are wrong. It has nothing to do with microwave
frequencies. A wave guide beyond cutoff is the mode that the tube is
operating in and it simply tells you that the frequency is too low for
the given size tube to propagate through. The energy inside the tube
gets shorted out. Many 2-30 mhz signal generators use that type
attenuator.

Now at 100 mHz
and below, while there would still a small but measurable difference of skin
effect at high transmit power, it ain't much and has nothing to do with low
power 2-30 mHz where a thin walled copper tube has ZERO measurable
difference in skin effect to a copper strap of even slightly smaller gage.

It has everything to do with it. Skin effect is ever present in all
conductors at ALL frequencies. Note my reference to 60 hz power
transmission where it is also important.

That has been my never paid attention to point all along, that skin effect
involves the entire cross section of thin material, and copper tubing is
more than thin enough to carry current in it's entire (that means from outer
to inner surface) cross section. That's exactly why copper tube is used so
much in AM broadcast components.

That is a contradiction to your point. You say that current flows
entirely through the walls of copper tubing and then say that is why
it is used in AM broadcast components. If that were true then they
would not use copper tubing but instead they would use solid copper
rod for better conduction.

The reason copper tubing is used is that there is no current of any
significance past a certain depth and to use solid rod would be a
waste of copper.

This is not even related to waveguides
which must by design AVOID all skin effect which causes great resistance and
heating at the current and velocites involved in microwave transmission.

Well, microwave transmissions don't travel any faster than HF
transmissions. But you might note that most wave guide inner surfaces
are silver plated to reduce skin losses.


As we eventually got around to research rather than blindly arguing
positions of opinion, then the participants hopefully learned something.
I've learned that applying the math from formulas for skin effect in
conductors of known ohmic value and used with a known frequency can
determine the wall thickness of a conductor which has full cross sectional
current on it. Guess what? The original poster's question about using copper
tubing remains answered. A 1" copper tube has more surface area and carries
just as much low power RF on it's entire cross section as a 1" wide piece of
copper strap that is nearly the same gage.


While skin effect is a gradient and not an absolute barrier, there is
current that flows at all levels in a conductor. Even on the inner
surface of your copper tube. But the amount of current there is so
small that it is immeasurable. It decreases exponentially.

One skin depth is defined as the depth at which the current has
dropped to about .37 times the current at the surface. (If you notice,
this is the same decay rate that a capacitor has when it charges or
discharges.) When you go that same distance (deeper) again the
remaining current will again drop to .37 times the current that it was
at the first skin depth.

So you can see that the current never reaches zero as you go deeper
but it only takes a few skin depths to decrease the current to a very
small value which is insignificant.

..0058" is the skin depth in copper at 200 khz. Skin depth decreases by
10 for each 100 times increase in frequency. So at 20 mhz the skin
depth would decrease by 100 from that. It gets pretty thin!


Skin effect is the reason coax cable works as it does. None of the RF
on the inside of the cable appears on the outside of the cable. Other
than leakage between strands of the shield of the cable. Those wire
strands on coax cable are pretty thin. Much thinner than your copper
pipe. Hard line has no leakage.

Regards
Gary


Best,

Jack Painter
Virginia Beach Va

"Gary Schafer" wrote

On Tue, 8 Jun 2004 17:05:53 -0400, "Jack Painter"
wrote:
"Gary Schafer" wrote

Look up "wave guide beyond cutoff". That will answer your question
about why rf dose not flow on the inside of a tube.

Right principles, wrong application. Trying to apply high power microwave
principles (3-15 gHz) to low power 2-30 mHz) is not the same.

Sorry Jack but you are wrong. It has nothing to do with microwave
frequencies. A wave guide beyond cutoff is the mode that the tube is
operating in and it simply tells you that the frequency is too low for
the given size tube to propagate through. The energy inside the tube
gets shorted out. Many 2-30 mhz signal generators use that type
attenuator.

Hi Gary, the difference that is relevant, I believe, is a waveguide for
microwave broadcast through the inside space of the guide, and there is
minmal current intentionally allowed on the waveguide. As I did explain,
skin effect must be avoided in microwave and it is due to the frequencies,
however it may be exploited in HF conductors which can eliminate wasted
center-core weight and cost. This is because of the drastically different
behavior of microwave from HF. And velocities inside a waveguide are much
faster than HF on a conductor. The attenuator you are describing allows
skin effect (it cannot avoid it either) but the true waveguide avoids it,
with the microwave reflecting off the walls of the guide. Hams can use a
tubing-shield to fox hunt in a building, but it is a stretch of the phrase
to call hiding a hh in the tube a wave guide beyond cutoff.

Now at 100 mHz
and below, while there would still a small but measurable difference of
skin
effect at high transmit power, it ain't much and has nothing to do with
low
power 2-30 mHz where a thin walled copper tube has ZERO measurable
difference in skin effect to a copper strap of even slightly smaller
gage.

It has everything to do with it. Skin effect is ever present in all
conductors at ALL frequencies. Note my reference to 60 hz power
transmission where it is also important.

Sorry Gary, that is not accurate. There is none in DC and very little until
VHF. It has no measureable difference to us for purposes of our discussion
between copper strap and copper tube at HF. Lightning would discover a
different impedance and pick the lower one, whichever that was. You or I or
any of our 150w or 1,000w radio equpment cannot tell the difference. By the
same math, 60hz has no skin effect for home wiring. Long, high power
transmission lines do not enter into a discussion about home wiring, and
neither should mircrowave or skin effect of copper tubing (which there is
none) enter into discussion about an RF ground on a sailboat or other low
power station. It is irrelevant between any copper conductors of similar
surface area and cross section.

While skin effect is a gradient and not an absolute barrier, there is
current that flows at all levels in a conductor. Even on the inner
surface of your copper tube. But the amount of current there is so
small that it is immeasurable. It decreases exponentially.

One skin depth is defined as the depth at which the current has
dropped to about .37 times the current at the surface. (If you notice,
this is the same decay rate that a capacitor has when it charges or
discharges.) When you go that same distance (deeper) again the
remaining current will again drop to .37 times the current that it was
at the first skin depth.

So you can see that the current never reaches zero as you go deeper
but it only takes a few skin depths to decrease the current to a very
small value which is insignificant.

.0058" is the skin depth in copper at 200 khz. Skin depth decreases by
10 for each 100 times increase in frequency. So at 20 mhz the skin
depth would decrease by 100 from that. It gets pretty thin!

Please check your premises. There is no standard depth for any frequency,
rather it varies drastically from one ohmic value of a given material
(conductor) to another. Since we're talking about copper, it's skin depth is
considered fully cross sectional at below 100 megahertz and a thickness of
..0025". At 15mhz on tubing or strap, it is using a full cross section to
carry power, not stray eddy currents. Design of course uses no more than the
proper combination of surface area and cross section to handle the required
frequency and power. Paper thin copper tape has limited usefulness to us,
because it can handle so little current, no matter how great it's surface
area. Copper tape amounts to roughly 1/3 the possible skin depth for copper
at HF, so it is just a cheap and poor alternative for copper strap. Thicker
than that, and we would be wasting center area that would carry little
current. Nobody said coax was the best conductor, it's just the most
economical. ;-)

Cheers,

Jack

Gary Schafer wrote in
:


Sorry Jack but you are wrong. It has nothing to do with microwave
frequencies. A wave guide beyond cutoff is the mode that the tube is
operating in and it simply tells you that the frequency is too low for
the given size tube to propagate through. The energy inside the tube
gets shorted out. Many 2-30 mhz signal generators use that type
attenuator.

And, if a Navy sailor has used them, the 50 ohm 1/8W resistors are cooked
from having transmitters keyed into the attenuators, too, negating any
possibility of CALIBRATION....Been there, fixed them for years for a
living...(c; Put your ohmmeter from the center pin of the output cable to
the shield and see if it measures 50 ohms....quick test.


It has everything to do with it. Skin effect is ever present in all
conductors at ALL frequencies. Note my reference to 60 hz power
transmission where it is also important.

Skin effect musta been why RG-8A melted when I keyed those twin 4-1000A
home brew linears I used to build into them...hee hee. I got accused of
hooking them up to the AC line to blow them at my ham club meeting. No,
wait, I think that was "dielectric heating" at 6KW....sorry. RG-17A/U
didn't melt.


That is a contradiction to your point. You say that current flows
entirely through the walls of copper tubing and then say that is why
it is used in AM broadcast components. If that were true then they
would not use copper tubing but instead they would use solid copper
rod for better conduction.

The reason copper tubing is used is that there is no current of any
significance past a certain depth and to use solid rod would be a
waste of copper.

Hogwash. They use copper tubing because it's cheap at the local air
conditioner supply house and because, if the station is above 5KW, copper
tubing COOLS itself better because it has a bigger radiating surface than
copper wire of the same cross section. Skin effect is immeasurable at 550-
1600 Khz.....or 20 Mhz, actually. Skin effect starts rearing its head up
in the VHF to UHF range where my 2 meter kilowatt used 2" copper plumbing
tubes and Ts for a plate tank for the 4CX250Bs in push pull.


As we eventually got around to research rather than blindly arguing
positions of opinion, then the participants hopefully learned
something. I've learned that applying the math from formulas for skin
effect in conductors of known ohmic value and used with a known
frequency can determine the wall thickness of a conductor which has
full cross sectional current on it. Guess what? The original poster's
question about using copper tubing remains answered. A 1" copper tube
has more surface area and carries just as much low power RF on it's
entire cross section as a 1" wide piece of copper strap that is nearly
the same gage.



Skin effect is the reason coax cable works as it does. None of the RF
on the inside of the cable appears on the outside of the cable. Other
than leakage between strands of the shield of the cable. Those wire
strands on coax cable are pretty thin. Much thinner than your copper
pipe. Hard line has no leakage.

Geez, all this time I was told it worked in TEM mode, with the H field
around the center conductor perpendicular to the E field from center
conductor to shield, with the RF flowing up the dielectric, like RF fields
will. I never heard of skin effect at, say, 20 Khz, where coax also works
just fine, properly terminated of course. I'm gonna call WWVB and warn
'em!

Lots of RF appears on the outside of cheap coax with chinzy braid, which is
why we double shield RG-6 on cable systems and use aluminum hardline to
keep the FCC from kicking our asses on the Aircraft Band near the airport.

Regards
Larry

This topic is interesting. I've seen a lot of opinions expressed,
some pretty startingly. Can you posters to this thread provide
some math and/or references?
Thanks,
Norm B

"engsol" wrote

This topic is interesting. I've seen a lot of opinions expressed,
some pretty startingly. Can you posters to this thread provide
some math and/or references?
Thanks,
Norm B

Norm, because acsii graphics for the formulas you requested do not display
well in newsgroups, here is a collection of the formulas and text from
various websites regarding skin effect:

http://members.cox.net/pc-usa/station/skineffect.htm

Best regards,
Jack