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Re: Copper braid and Copper strap (was Re: About copper strap)

At 11:41 AM 5/6/99 -0600, you wrote:
>Hello Reinhard,
>
>  I have a question regarding your statement that copper braid is worthless
>for rf work; what do you base this assertion on?
>I utilize 1/4" tinned copper braid as the main leads in a device which
>utilizes rf to inductively illuminate a plasma tube.  It works EXTREMELY
>well and I have not even considered using anything else; am I missing out on
>something by using the braid?  Granted, it does get hot, so maybe there is
>something to what you're saying about shorting out, but do you really think
>copper strap will work better in the transmission of rf?
>
>I look forward to your reply.
>
>Best regards,
>                             Trent


Hi Trent,

	No doubt about it.  Copper strap is MUCH better than braid.  Copper braid
will often work but if you need very high current capability, silver plated
copper is the best you can get.  I work with very high power RF equipment
that can push thousands of amps of RF.  We use silver plated copper pipe
with water flowing through it.  We have tested EVERYTHING at one time or
another and silver plated smooth copper surface is the choice if you need
very high RF currents.  The skin depth of RF currents allows current to
flow only in the a very thin layer near the surface of the metal (often
less than 0.001").  Thus, the braid looks much more resistive than a bare
strap.  I suggest you try it in you circuit.  You will be very surprised to
see how much cooler it runs...  

However.... be careful of trying this in commercial equipment.  Sometimes
this equipment is "designed" to have loss in a braided conductor.  Suddenly
"improving" the circuit by using strap can blow the thing up. - Been there,
done that... :-))

It is interesting that the silver plating is not really to help the
conductivity but to fight tarnish.  Unlike many metals, when silver
tarnishes, the tarnish is still very conductive....

I cut and pasted a post from the old days on this here....

	Terry

BTW - I hope you are not one of our competitors :-))  If you are, try using
lead! :-))


=================================
---------- Forwarded message ---------- 
Date: Wed, 8 Jul 1998 12:12:24 -0600 
From: terryf-at-verinet-dot-com 
To: Tesla List <tesla-at-pupman-dot-com> 
Subject: Re: RE>Best sparks (fwd) 

Hi Dale, 

Thanks for this info. Since Resistance = Length / ( Conductivity * Area )
the higher ( Conductivity * Area ) is, the lower the resistance. I added
the conductivities and multiplied them out: 

Material 	Skin Depth 	Conductivity 	SD*C 
Silver 	.064 		6.1 		0.3904 
Copper 	.066 		5.7 		0.3762 
Gold 		.075 		4.1 		0.3075 
Aluminum 	.085 		3.5 		0.2975 
Chromium 	.081 		?	 
Nickel 	.014 		? 
Brass		.126		1.1		0.1386
Magnetic Iron	.011		.2		0.0022
Mumetal	.00029		?

SD in in mm at 1MHz
Conductivity is x 10^-7

Silver and copper are the winners here. Mumetal will loose badly. 

As mentioned in a past post, Aluminum has very thick oxide layers (Aluminum
oxide is a very good insulator) that really screws up it's conductivity in
practice. We use silver plated copper conductors for high current (100+
amps 13 MHZ) RF conductors. Silver oxide is fairly conductive. Thin gold
over copper is probably the best. A copper sphere plated with gold would be
really neat!. However, not very cheap. Silver plated copper is best on
paper but in practice the oxide would look bad. The gold over copper would
give the best performance while not having the oxidation problem and would
look good. 

Terry Fritz