[Amps] Skin Effect and Wire Current Capacity at HF

[R@contesting.com]

On Apr 14, 2005, at 10:22 PM, Dan Levin wrote:

> I'm trying to design a coil that will be used in a 1500 watt filter at 
> HF.
> I know that I need to allow for frequency related skin effect that will
> reduce the area of the wire or tubing carrying the current.
>
> First, I check the ARRL Handbook and the Antenna Book. No formula and 
> no
> table showing suggested wire sizes for a given frequency and power 
> level.
>
> Next, I determine that the skin depth at 28 mHz is .0005", and I 
> calculate
> the copper volume that the current is traveling through at one skin 
> depth in
> wires and tubes of various sizes.  I get results that seem 
> unreasonable -
> using a current density of 2500 amps / square inch I get a current 
> capacity
> for #14 wire at 28 mHz of under .5 amps and for 1/2" tubing of just a 
> couple
> of amps.  Yes, I realize that the skin depth is one standard 
> deviation, but
> even allowing for that the capacities seem very low.

E. F. Johnson rated its #14 gauge Cu roller coil at 3A @ 30MHz.
>
> Can someone point me at either a formula or a table that will tell me 
> or
> allow me to calculate what the current capacity of a wire or tube is 
> at a
> given HF frequency?  Or, I suppose to put it differently since the 
> capacity
> is related to the acceptable temperature rise - something that will 
> tell me
> the copper loss in a piece of wire or tubing at a given frequency?
>
> Thanks!
>
> 			***dan, K6IF
>
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Rich Measures, 805.386.3734, AG6K, www.somis.org