[TowerTalk] Loading Coils

[Richard (Rick) Karlquist]

WOW!  Many thanks to Wes for finding this obscure, but extremely 
valuable paper and posting it to TT.  Whenever Wes posts here, I make 
sure to read the post.  This paper completely debunks huge amounts of 
folklore.  It confirms various suspicions I have always had, such as the 
fact that the magnetic parameters of nickel at RF are unpredictable so 
it is safe to assume they are very bad, and that nickel should never be 
used for RF coils.  I have been a consultant to a lot of companies doing 
high power RF and I am always on the look out for nickel plating.  The 
clients will tell me how great nickel is for various reasons.  But I 
have to tell gently tell them it is a non starter for RF.  No the 
customer is not always right.

The company I currently work for has air core inductors custom made 
using ordinary tinned copper bus wire.  I have measured the inductance 
of these coils and it compares very favorably with the predicted Q of 
our coils if bare copper wire were used.  (See Medhurst's 1947 paper on 
the subject).  Tin does have considerably lower conductivity vs copper, 
but at least it is non-magnetic.  Also, the thickness of the tin plating 
is so thin that it is negligible in terms of skin depth.  Even when it 
is old wire that is no longer shiny bright, it still doesn't ding the Q.
At least for indoor work, tinned copper for my money is the way to go.

73
Rick N6RK

On 8/2/2025 10:15 AM, Wes wrote:
> Actually, I know it's a bad idea, see top of page 151 of the following.
> 
> https://www.dropbox.com/scl/fi/w5u2m0qvuwjs0i3vlwdsf/Plating.pdf? 
> rlkey=n99dlrd2joh5548drtczvtsks&st=grysczj9&dl=0
> 
> On 8/1/2025 2:29 PM, Wes wrote:
>> I would need some convincing that nickle plating is a good idea.
>>
>> Wes  N7WS
>>
> 
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