On Sun, 12 Oct 2003 01:33:19 GMT, "Frank Dresser"
wrote:


"Dale Parfitt" wrote in message
...

For HF, I totally agree. My passion is 1296 MHz Moonbounce- and silver
plated
cavities are a must for high efficiency.

Dale W4OP

Got news for you. skin depth IS a big deal at SW freuquencies as well.
For copper is it roughy 6.6/(f^.5) in cm....

The skin depth at 1 Mhz in copper is a whopping .066 mm. That is about
2 mils (1/500th of an inch). That is why copperweld wire (copper
over steel) works as well as pure copper for an antenna.

And yes, it is a bigger deal 1Ghz, but a 1 micron silver plate is
about all it takes. Skin depth in copper at that frequency is .0021
mm, or about .07 mils, one 15,000th of an inch in copper, in Silver it
would be more like 1/20,000th of an inch.

Even at 60hz, it doesn't pay to use a conductor larger then an inch in
diameter. Skin depth at 60Hz in copper is .85cm
Sure. Skin effect is a big deal at 100 times a typical SW frequency. It's
also important inside IF and some RF transformers. Have you ever seen ads
for those expensive audio cables in which they make a big deal the skin
effect? To paraphrase some comedian -- "Being an audiophool is God's way of
saying you have too much money".

Frank Dresser

On Sun, 12 Oct 2003 18:37:51 -0400, "AbbN"
wrote:

Hi,

How about using the ground in a 3 prong electrical socket???? Better than
nothing??? Dangerous??? I'm in a high rise
These are often very poor radio frequency grounds. A DC ground, or
for that matter a 60Hz ground has a very large skin depth (about .85cm
at 60Hz), so the entire conductor is useful, and the DC resistance to
ground is about all you have to worry about.

A good DC or even 60Hz ground can be an awful Radio frequency ground.
Even at 1 Mhz, the skin depth is a small fraction of a 1 mm, so all of
the corrosion and garbage occurs on the part of the conductor you
need. In addition the length of wire to the physical ground can be
very large, and even a straight wire has inductance, so long ground
line in addition to having poor conductivity, may also have
substantial inductance. Both make for a high impedance path to ground,
which is the last thing you want.

If it is a steel frame building, the building frame is probably a
much better RF ground then the ground lead in an outlet.

"matt weber" wrote in message
...
On Sun, 12 Oct 2003 01:33:19 GMT, "Frank Dresser"
wrote:


"Dale Parfitt" wrote in message
...

For HF, I totally agree. My passion is 1296 MHz Moonbounce- and silver
plated
cavities are a must for high efficiency.

Dale W4OP

Got news for you. skin depth IS a big deal at SW freuquencies as well.
For copper is it roughy 6.6/(f^.5) in cm....

The skin depth at 1 Mhz in copper is a whopping .066 mm. That is about
2 mils (1/500th of an inch). That is why copperweld wire (copper
over steel) works as well as pure copper for an antenna.

Well, thanks for the newsflash. I guess that means that skin effect isn't
worth worrying about for 99% of the work SWLs do. Like antennas and ground
wires.


And yes, it is a bigger deal 1Ghz, but a 1 micron silver plate is
about all it takes. Skin depth in copper at that frequency is .0021
mm, or about .07 mils, one 15,000th of an inch in copper, in Silver it
would be more like 1/20,000th of an inch.


Wow. That must mean that skin effect makes a difference in the hair fine
wires oftentimes found in IF and RF transformers used in SW radios. Maybe
1% of SWLs will be dealing with such things.

Even at 60hz, it doesn't pay to use a conductor larger then an inch in
diameter. Skin depth at 60Hz in copper is .85cm
Sure. Skin effect is a big deal at 100 times a typical SW frequency.
It's
also important inside IF and some RF transformers. Have you ever seen ads
for those expensive audio cables in which they make a big deal the skin
effect? To paraphrase some comedian -- "Being an audiophool is God's way
of
saying you have too much money".

Frank Dresser



Frank Dresser

"matt weber" wrote in message
...
On Sun, 12 Oct 2003 18:37:51 -0400, "AbbN"
wrote:

Hi,

How about using the ground in a 3 prong electrical socket???? Better than
nothing??? Dangerous??? I'm in a high rise
These are often very poor radio frequency grounds. A DC ground, or
for that matter a 60Hz ground has a very large skin depth (about .85cm
at 60Hz), so the entire conductor is useful, and the DC resistance to
ground is about all you have to worry about.

A good DC or even 60Hz ground can be an awful Radio frequency ground.
Even at 1 Mhz, the skin depth is a small fraction of a 1 mm, so all of
the corrosion and garbage occurs on the part of the conductor you
need.


Wait a minute. Are you saying the depth of the skin effect is the same for
poor conductors as good ones? Wouldn't the increased skin depth of a poor
conductor get the current down to the good conductor?


In addition the length of wire to the physical ground can be
very large, and even a straight wire has inductance, so long ground
line in addition to having poor conductivity, may also have
substantial inductance. Both make for a high impedance path to ground,
which is the last thing you want.

Inductance and capacitance! And they work together in such a way that if
your ground conductor is 1/4 wave or an odd multiple of a 1/4 wave it
presents such a high impedance that it isn't an RF ground at all :-(.

But wait. It still might work just fine, because now it's a counterpoise
:-)!



If it is a steel frame building, the building frame is probably a
much better RF ground then the ground lead in an outlet.

Steel frame buildings are almost always commercial buildings. Shouldn't you
ask the building supervisor to help find the framing and punch a hole
through the wallboard? And wouldn't the steel beams have a thicker buildup
of rust and paint and crud than galvanized steel conduit?

To the original poster, I say -- Experiment safely and keep track of your
results!

Frank Dresser