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Re: [Amps] Circuit Board Question

Subject: Re: [Amps] Circuit Board Question
From: "" <>
Date: Fri, 1 Aug 2014 09:46:35 +0100 (BST)
List-post: <">>
According to the ITT 'Reference data for radio engineers', 3 oz (0.0042inches 
thick) copper will give you 3.5 skin depths at 1.8 MHz.
At 30 MHz, one skin depth is 0.00048 inches.

At DC and LF, a conductor width of 0.1 inch would give you a temperature rise 
of 10C at 10 amps. (MIL-STD-275C)

I would use about 0.2 inch spacing, but if the unit is where condensation can 
be a problem, it would be worth using a coating of varnish.

My switching unit uses a normal receiving type ceramic switch, about 1.25 
inches across, with clips on both sides, driven by a Ledex. The traces are 50 
ohm traces on 1 oz copper (about 3/16 inches wide or so), none more than about 
3 inches long. The SWR is about 1.2 at 30 MHz and it has been running quite 
happily since 1996 in an unheated shed at the base of the tower. No varnish on 
the board, just a tin dip.


Peter G3RZP

----Original message----
>From :
Date : 01/08/14 - 07:19 (GMTDT)
To :,
Subject : [Amps] Circuit Board Question

Could someone help me out with some advice.


How much separation between circuit board traces in an antenna switch box
would be recommended to reliably handle the voltage associated with legal
limit at 2:1 SWR?

Just tinned or conformal coating?

How wide would you recommend the trace to handle the same signal using 3oz
board stock - longest trace is about 2", most less than 1"?


Thanks in advance



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