[Amps] Skin Effect and Wire Current Capacity at HF

[Carcia, Francis A HS]

I think it was 1 KW input am modulated so close enough.

-----Original Message-----
From: Will Matney [mailto:craxd1 at ezwv.com]
Sent: Friday, April 15, 2005 2:11 PM
To: amps at contesting.com
Subject: Re: [Amps] Skin Effect and Wire Current Capacity at HF


Dan,

Check some of the earlier handbooks back in the 80's or 70's. They did have
a table in there for frequency and power to wire size. At 30 MHz, you'll
need around 3/16"-1/4" copper tubing for the coil at 1500 watts. As
frequency drops, the size drops.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 4/14/05 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.
>
>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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