"Gary Schafer" wrote

Jack, I don't know what you have been reading in regards to skin
effect but it is very real and present.

Hi Gary, when a poster asked for the formulas for this discussion, I could
not display them in the newsgroup (ascii) so I pasted several of them on a
website.....

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


I don't know what you mean "there is no standard depth for any
frequency"? It is well known.

The resistance of a particular conductor, not just it's material, must be
known to calculate skin depth. Averaging it with constants will produce the
wide variety of depths that are seen in different formulas and tables.

At 60 hz the skin depth is around 1/3 of an inch. Very significant in
a power transmission cable. Or a lightning ground cable..
Look up any large power cable ratings and you will usually find a DC
resistance specified and an AC resistance also specified. The AC
resistance is due to skin effect.

Yes I agreed with you it is relevant only at very high power or long lengths
when inductive reactance becomes as important as DC resistance.

Here are some figures on skin depth for copper: Skin depth (in mils) =
2.602/(sq. root of frequency in Mhz). At 1.8 Mhz it's 1.94 mils or
.00194 inches, just under 2 thousandths. It decreases as the inverse
square root of frequency so at twice the frequency it will be .707
times as deep, and half as deep at 4 times the frequency. At 29.7 Mhz
it's about half a thousandth. At 4 or 5 skin depths any additional
thickness ceases to have additional value.

Gary, the problem with using those constants is, again, it will allow you to
reduce the skin depth to nearly nothing, when in fact below a certain cross
section at HF frequencies, formula predictions for skin depth cease to be
relevant. The current, assumed to be constant, cannot continue to use less
and less cross section until it has nothing to work with. The formulas are
an approximation that allows designers to consider the resistance casued by
skin effect and use an appropriately sized conductor. For instance, I could
not use 1,000w on thin RG-8X if your application from a table using
constants was accurate. At 5 mhz there is considerable cross section of that
small diameter center conductor carrying current. That is why the center
conductors are not paper-thin hollow tubes the way the outer shield _can_
be. Do you agree?

Best,

Jack

On Wed, 9 Jun 2004 13:40:29 -0400, "Jack Painter"
wrote:

"Gary Schafer" wrote

Jack, I don't know what you have been reading in regards to skin
effect but it is very real and present.

Hi Gary, when a poster asked for the formulas for this discussion, I could
not display them in the newsgroup (ascii) so I pasted several of them on a
website.....

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


I don't know what you mean "there is no standard depth for any
frequency"? It is well known.

The resistance of a particular conductor, not just it's material, must be
known to calculate skin depth. Averaging it with constants will produce the
wide variety of depths that are seen in different formulas and tables.

Yes it depends on the shape too. A round conductor will be slightly
different than a flat conductor but for our purposes it is in the ball
park. The constant comes from actual calculations. The constant makes
it easier than going through all the math to obtain the constant.


At 60 hz the skin depth is around 1/3 of an inch. Very significant in
a power transmission cable. Or a lightning ground cable..
Look up any large power cable ratings and you will usually find a DC
resistance specified and an AC resistance also specified. The AC
resistance is due to skin effect.

Yes I agreed with you it is relevant only at very high power or long lengths
when inductive reactance becomes as important as DC resistance.

The AC resistance that I am referring to has nothing to do with any
reactance due to cable length. Reactance is of course another factor
that enters into the picture but AC resistance in this case is
referring to that resistance caused by skin effect. Not reactance.


Here are some figures on skin depth for copper: Skin depth (in mils) =
2.602/(sq. root of frequency in Mhz). At 1.8 Mhz it's 1.94 mils or
.00194 inches, just under 2 thousandths. It decreases as the inverse
square root of frequency so at twice the frequency it will be .707
times as deep, and half as deep at 4 times the frequency. At 29.7 Mhz
it's about half a thousandth. At 4 or 5 skin depths any additional
thickness ceases to have additional value.

Gary, the problem with using those constants is, again, it will allow you to
reduce the skin depth to nearly nothing, when in fact below a certain cross
section at HF frequencies, formula predictions for skin depth cease to be
relevant. The current, assumed to be constant, cannot continue to use less
and less cross section until it has nothing to work with. The formulas are
an approximation that allows designers to consider the resistance casued by
skin effect and use an appropriately sized conductor. For instance, I could
not use 1,000w on thin RG-8X if your application from a table using
constants was accurate. At 5 mhz there is considerable cross section of that
small diameter center conductor carrying current. That is why the center
conductors are not paper-thin hollow tubes the way the outer shield _can_
be. Do you agree?

RG-8X will get a little warm with 1000 watts on it.
The main reason the center conductors are not paper thin hollow tubes
is because of physical restraints. If your argument would hold up then
none of the hard line coax would have hollow tubing for their center
conductors. Some of it is used in extremely high power at HF as well
as UHF. Only the outer surface of the center conductor is of much
importance in conduction.

While it is true that it gets more complicated to predict actual skin
effect on a thin conductor because as said before, the current does
not completely stop at a certain depth. It decreases exponentially.
But usually 4 or 5 skin depths are sufficient for all practical
purposes.

At that depth of 4 skin depths less than 2% of the current on the
surface will be present. We use .37 as a skin depth but .368 is closer
to what it works out to. .368 x .368 x .368 x .368 = .183 or 1.83%

But I think the original argument was whether or not the same current
or any current would flow on the inside of a copper tube at HF.
It goes away quickly and can't propagate inside as explained earlier.

Regards
Gary


Best,

Jack

In article ,
Gary Schafer wrote:


snipped because we all know this stuff.......right?




Now how can you argue with that! :)

Regards
Gary


Gary, I think that your "Beating a Dead Horse" here....Jack just isn't
going to get it. Seems he can't wrap his mind around Physics 101.
Very nice explanations, though.......

Bruce in alaska
--
add a 2 before @

On Thu, 10 Jun 2004 03:09:50 GMT, Bruce in Alaska
wrote:

In article ,
Gary Schafer wrote:


snipped because we all know this stuff.......right?




Now how can you argue with that! :)

Regards
Gary


Gary, I think that your "Beating a Dead Horse" here....Jack just isn't
going to get it. Seems he can't wrap his mind around Physics 101.
Very nice explanations, though.......

Bruce in alaska


Thanks Bruce. I do think he has the blinders tightly strapped on.

Regards
Gary

"Jack Painter" wrote in
news:Vlxxc.5736$5B2.5631@lakeread04:

Larry, we've probably had the details of this antenna system in pieces
across various posts, but would you mind putting in one place here?
Sounds like an intersting and well thought out setup.

Thanks,

Jack

It isn't very fancy, actually. The Icom AT-140 tuner is screwed to the top
of the aft cabin just aft of the mizzen mast, which is deck stepped. The
HV RF output post is about 8" from the base of the insulated backstay on
the main and a short, smoothly bent piece of #12 Copperweld antenna wire is
hose clamped to the Amel's backstay jack out of the way of the winch handle
socket. The insulator is about a ft from the mast at the top and every
time I look up there I want an insulator on each end of the triatic stay
with an interconnecting Copperweld wire connecting the top of the backstay
antenna to the center of the insulated triatic to make it a capacitor hat
on top of the 50' sloping vertical for the lower frequency bands. If it
ever goes back into the yard for demasting, it will have it...(c; But, for
now, it just has the backstay.

When Geoffrey got the boat, the previous owner reported poor performance
(he was a ham, too) from the backstay antenna, which I traced down to
loading from the stainless cable topping lift on the large main boom,
sucking off the signal to the mast because when the boom was centered, it
was only a few inches from the backstay. Not good. So, we changed the
stainless to nylon and now no metal gets near the antenna, no matter where
the boom is set. Signal reports came up a LOT!

Directly beneath the tuner, in the support for the deck stepped mast, are
several storage holes I can put wires into. So, I got a #8 battery wire,
black of course, and put a ring terminal to fit the ground post on the
tuner on one end. As straight as I could, I routed it down through the
openings in the mount into the engine compartment which is right under the
mast. Directly under the tuner, too, is the DC shunt used for the ampere-
hour meter on the house batteries under the shunt. This great ground, to
the big 700 AH house batteries against the hull, and the whole house ground
system, is tied in at the shunt, then the cable drops straight down to the
engine block for more grounding and capacitive coupling through the hull.
Antenna current came way up as did signal reports from this installation.
Dropping a bare Copperweld wire over the side I use for even more grounding
while underway at sea, I measure only about 1.5 ohms from the bare wire
laying on the bottom of the marina and this ground connection above.
Something's got a great connection to the ocean down there. I musta got
lucky.

That's it. The radio is grounded to a ground strap Amel installed behind
the panel behind the chart table. It's a common ground strap where all my
instrumentation, navigation and communications is tied with small wire.
There is a direct connection between that strap at the nav station and the
engine block and house ground, too. I like to think it may bypass some
static hits, but haven't been through any on this boat....yet. Let's not
rush the testing of this theory.

Larry W4CSC

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

On Fri, 11 Jun 2004 23:03:16 -0000, Larry W4CSC
wrote:

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.

You were right the first time. Dielectric loss is not a factor below
100 mhz. Only lack of large enough conductor surface area causes
heating / loss.



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.


Nooo ooo, not you too Larry. Did it occur to you that copper tubing
with the same cross section as copper wire has much greater SURFACE
AREA? That would help with cooling and also, believe it or not reduce
skin effect so it didn't get as hot in the first place.

Ever heard of litz wire? I am sure you have. It is often used in small
coils to reduce skin effect losses. And guess what, it is most
effective below frequencies of 1 mhz. So if skin effect was not a
factor at those low frequencies what would be the need for litz wire?

Got any old 10khz or 50 khz coils laying around? I bet you will find
some litz wire in them. The old command set receivers with the 85 khz
IF's are wound with litz wire. Wanna guess why.


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!

Oh I am sure they already know about it!
Next time you are playing with your big amp tuning your mobile
antenna, try swapping out your solid wire loading coil with the same
size copper tubing for a coil and see if either one gets any hotter.
If skin effect doesn't exist then your solid copper coil should be
much cooler of the two.

Regards
Gary


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

"Larry W4CSC" wrote

It isn't very fancy, actually. The Icom AT-140 tuner is screwed to the
top
of the aft cabin just aft of the mizzen mast, which is deck stepped. The
HV RF output post is about 8" from the base of the insulated backstay on
the main and a short, smoothly bent piece of #12 Copperweld antenna wire
is
hose clamped to the Amel's backstay jack out of the way of the winch
handle
socket. The insulator is about a ft from the mast at the top and every
time I look up there I want an insulator on each end of the triatic stay
with an interconnecting Copperweld wire connecting the top of the backstay
antenna to the center of the insulated triatic to make it a capacitor hat
on top of the 50' sloping vertical for the lower frequency bands. If it
ever goes back into the yard for demasting, it will have it...(c; But,
for
now, it just has the backstay.

When Geoffrey got the boat, the previous owner reported poor performance
(he was a ham, too) from the backstay antenna, which I traced down to
loading from the stainless cable topping lift on the large main boom,
sucking off the signal to the mast because when the boom was centered, it
was only a few inches from the backstay. Not good. So, we changed the
stainless to nylon and now no metal gets near the antenna, no matter where
the boom is set. Signal reports came up a LOT!

Directly beneath the tuner, in the support for the deck stepped mast, are
several storage holes I can put wires into. So, I got a #8 battery wire,
black of course, and put a ring terminal to fit the ground post on the
tuner on one end. As straight as I could, I routed it down through the
openings in the mount into the engine compartment which is right under the
mast. Directly under the tuner, too, is the DC shunt used for the ampere-
hour meter on the house batteries under the shunt. This great ground, to
the big 700 AH house batteries against the hull, and the whole house
ground
system, is tied in at the shunt, then the cable drops straight down to the
engine block for more grounding and capacitive coupling through the hull.
Antenna current came way up as did signal reports from this installation.
Dropping a bare Copperweld wire over the side I use for even more
grounding
while underway at sea, I measure only about 1.5 ohms from the bare wire
laying on the bottom of the marina and this ground connection above.
Something's got a great connection to the ocean down there. I musta got
lucky.

That's it. The radio is grounded to a ground strap Amel installed behind
the panel behind the chart table. It's a common ground strap where all my
instrumentation, navigation and communications is tied with small wire.
There is a direct connection between that strap at the nav station and the
engine block and house ground, too. I like to think it may bypass some
static hits, but haven't been through any on this boat....yet. Let's not
rush the testing of this theory.

Larry W4CSC

Sounds great Larry, Thanks. Seen in a Univ of Florida study, paraphrased:

1. All boats can be struck by lightning, protected or not, and
2. Protected boats and unprotected boats both suffer damage when hit, and
3. Unprotected boats suffer significantly more damage than protected boats.

It sounds like you and Lionheart are well protected.

I remember a night of terrible line squalls that wrecked several yachts in
Block Island Salt Harbor. I had stayed up on deck with gear on as I knew it
was coming as I returned from a night on the town. It was worse than any
summer line squall should have been! By the time I roused my family the
winds had the entire harbor dragging anchor. Anyne who has been there can
imagine the panic of watching your Out Island 41 heading toward mega-million
yachts both dragging along with you, and lining the docks for a busy
weekend. The Westerbeke diesel with one anchor could not hold us, and I went
forward to set a second anchor and lots of chain with it. I think there must
have been hundreds of lightning srtikes all around us without any break
between them. Night turned to day, and that helped avoid touching shrouds
while on deck. Everything around us seemed to be getting hit, and of course
it was one of those moments when (at least I) thought I was going to die
from lightning at any moment. But the second anchor and the diesel held us
just short of one of the hundred-footers at the outer docks. In the
aftermath, we heard there was a lot more damage from collisions than from
lightning, and that is amazing considering how many yachts I saw get struck
that night.

Best,

Jack

"Jack Painter" wrote in
news:16syc.157$Jk5.41@lakeread02:

outer docks. In the aftermath, we heard there was a lot more damage
from collisions than from lightning, and that is amazing considering
how many yachts I saw get struck that night.

I've read the webpage from FL. Very interesting research. The mast looks
tall when you're standing at the bottom of it looking up, but in the
overall height of a thunderstorm FIVE MILES HIGH, our masts are like a
dimple on the dining room table, and not much of a "target".

I was at the transmitter shack of WRJA-TV, the PBS station in Sumter, SC,
visiting an old friend who was chief engineer, Bill Jones, one night. We
were building the first weather radio repeater after Bill had applied for,
and gotten, an FCC license for that band to simply repeat the signal from
Columbia, SC's weather station to the local Sumter area which had trouble
hearing it. We made it out of kit ham radio repeater boards from VHF
Engineering in Binghamton, NY, as we had a local repeater.

A huge thunderstorm cell moved across Sumter and actually went THROUGH the
1800' WRJA-TV tower while we watched out the back door as lightning went
SIDEWAYS 10 miles in the cloud just to hit that big 1800' ground rod
sticking up out of the table-flat terrain of eastern Sumter County. I'm
standing there watching the light show and suddenly Bill taps me on the
shoulder and hands me a big yellow rain coat, saying, "Come on. I wanna
show you something neat." We followed the huge hardline coaxial cables
from the 35KW TV transmitter out to the base of the antenna and Bill says,
"You're standing in the safest place in Sumter County. There is a cone of
protection against being hit by lightning provided by my tower and you're
now standing in the middle of it. Hang onto the tower leg and feel the
current going through it." I burned my hand a couple of times as the huge
BOOMs went off over my head a thousand feet up. The huge bridge cables
JUMPED from the surge of electrical EMP hit them, many times. The lights
went out and we had to go back in the building to reset the transmitters
when the power came back on.

Though the "tower" on the sailboat is very short, in comparison, I like to
think that if you have a proper grounding system, like the professor
describes on his webpages, you are also in a tiny cone where the blast will
mostly be shunted AROUND you, which is why your car is so safe in a
thunderstorm. The current surge that kills goes AROUND the the steel body
of the car....Steel ships and boats do that....Plastic, not so good.

Larry

(sigh)