Sri, gang; the Scot, Maxwell, and the Englishman, Heaviside, decree
that RF will still concentrate on the outside of a conductor. The
distribution of current in depth is an exponential function, but the
effective skin thickness, in copper, is 0.0026" at 1 MHz, 0.000826" at
10 MHz, and 0.00026" at 100 MHz. Reference _Radio-Electronic
Transmission Fundamentals,_ B. Whitfield, Jr. It is a semi-technical
book, long out of print, that offers good explanations for the
non-engineer qualified ham. It is worth searching for on the used book
market. Meanwhile, copy those numbers and paste them where you can find
them. When calculating the resistance of a copper conductor, don't use
the cross sectional area, use the circumference times the effective skin
depth to calculate the effective area of conduction.
Another advantage of strap, or widely spaced wires, is reduced
inductance per unit length, compared with a cylinder of similar
circumference.
1994 Radio Amateurs' Handbook, page 2-20, providing the following
formulae:
For a flat strap:
L = 0.00508b[ln (2b/(w+h) + 0.5 + 0.2236 (w+h)/b]
where
L = inductance in microhenrys
b = length in inches
w = width in inches
h = thickness in inches.
For a round wire:
L = 0.0002b[(ln(2b/a)) - 0.75]
where L = inductance in microhenrys
a = wire radius in mm
b = wire length in mm
ln is the natural logarithm
Sorry about the change from inches to mm. I'm quoting ARRL. I believe
the following is correct with the dimensions in inches:
L = 0.00508b[(ln(2b/a)) - 0.75]
Inductance of parallel wires spaced apart approximates the inductance of
parallel inductors. Their paralleled resistance is also lower than that
of a single wire at HF frequency if the total circumference or surface
area is greater, assuming the material is the same.
73 de WOØW
JC Smith wrote:
> What if
>you slit the copper tube before using it, would that be enough to allow both
>the inside and outside to conduct high frequency current?
>
>
>
>
>
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