Richard Harrison wrote:
Art wrote:
"David just for the record, skin depth is proportional to
frequency----."

Not exactly. Skin depth is inversely proportional to the square root of
the frequency.

For example at 1 Hz the skin depth is about 2.6 in. in copper. At 10 Hz.
it is about 0.826 in. and at 100 Hz the depth is about 0.260 in. and at
1000 Hz the depth is 0.0826 in. etc.

Best regards, Richard Harrison, KB5WZI

Actually, skin depth is inversely proportional to the square root of
frequency only in a good conductor like copper. Some common materials
like dirt are fairly good conductors at low frequencies but behave more
like dielectrics at higher frequencies. And skin depth doesn't change
with frequency in a dielectric. For "average" ground (0.005 S/m
conductivity, permittivity of 13), the transition between conductor
behavior and dielectric behavior is at about 6.9 MHz, in the middle of
the HF range. Well below that frequency, the skin depth changes in
inverse proportion to the square root of the frequency; above it, the
skin depth stays nearly constant. For "average" ground:

Freq MHz Skin Depth m
0.01 71.2
0.5 10.4
1 7.6
2 5.8
4 4.7
6.9 4.2
8 4.1
16 3.9
100 3.8

Roy Lewallen, W7EL