[Amps] Skin depth: silver plating of tank circuit coil feasible with

[Steve Thompson]

I recall an article in RF Design magazine which suggested that the 
rf current moves away from high resistivity, I think there was 
some maths supporting the analysis. If the outer surface of a 
(e.g. copper) conductor oxidises, the article predicted that the 
current just moves deeper into the pure metal so the difference in 
performance is much less than might be expected.

Steve

>   Take a look at http://www.bnk.com/w0qe/inductor_Q_tests.html where I 
> made a bunch of measurements.
> 
> Silver is a 7% better conductor than copper but at RF the skin depth is 
> inversely proportional to the conductivity so the gain you get from 
> heavy silver plating is only about 3.5% to 4%.  You would be better off 
> to just increase the copper wire size by 1.  As far as beauty is 
> concerned, painting or clear coating the copper has no effect at HF.  
> All the stuff you hear about oxides of silver being conductors are BS.
> 
> Larry, W0QE
> 
> On 10/4/2010 8:01 AM, Carl wrote:
>> ----- Original Message -----
>> From: "Dr. David Kirkby"<david.kirkby at onetel.net>
>> To:<amps at contesting.com>
>> Sent: Monday, October 04, 2010 8:08 AM
>> Subject: Re: [Amps] Skin depth: silver plating of tank circuit coil feasible
>> with chemical plating kits?
>>
>>
>>> On 10/ 4/10 12:42 PM, LB3HC wrote:
>>>> I am working on some loss estimates for the tank circuit of my GS35B
>>>> amp. design and I am considering if silver plating of the tank circuit
>>>> coil is feasible or not. I intend to use copper tubing intended for
>>>> camping gas installations in the tank coil(s), as it is readily
>>>> available. According to VE1ALQ's tool, the 3 times skin depth for RF
>>>> current on 10 meters wavelength is 36 Microns.  Silver plating kits
>>>> that are available on the market** typically states a plating
>>>> thickness of 70 micro inches, which is only 1,7 microns. This is 1/20
>>>> of what is necessary to have silver down to the 3 x skin depth, if my
>>>> calculations are correct.
>>>>
>>>> What are your experiences with silver coated contra non coated tank
>>>> coils?
>>>>
>>>> Polishing the copper tubing will reduce the RF skin current resistance
>>>> according to some sources. Is this true, and in case it is, what are
>>>> the mechanisms that makes polished copper conduct better (RF) than non
>>>> polished copper?
>>>>
>>>> **
>>>> http://www.cool-amp.com/product%20info/COOL-AMP%20One-page%20Info%20Sheet%20&%20inserts%20%28FINAL%2004.30.09%29.pdf
>>>>
>>>> 73
>>>> LB3HC
>>> I don't know the depth, but I know I had a 2 m anode line silver plated
>>> for a
>>> dual 4CX250B amplifier. Careful measurements before and after plating
>>> showed no
>>> statistically significant difference. The line was brass, which is a
>>> poorer
>>> conductor than copper, so the difference between brass+silver should have
>>> been
>>> better than between copper+silver. But it was a waste of time - other than
>>> it
>>> looked nicer!
>>>
>>> A friend got the plating done free, and I know it was deeper than normally
>>> done,
>>> though I can't recall the depth.
>>>
>>> You really are wasting your time at 10 m if you think you will improve
>>> efficiency. Anybody that tells you that it made a difference at that
>>> frequency
>>> is kidding themselves.
>>>
>>> If anything, gold plating would be more useful, as it would stop
>>> oxidation. In
>>> which case, you need only a very thin coat - forget about skin depth. 99%
>>> of the
>>> current will be in the copper, not in the gold, but the gold will stop
>>> oxidization.
>>>
>>> Oxidization might be one of the advantages of cleaning the copper, but I
>>> don't
>>> really think it will make much difference until you reach a few GHz.
>>>
>>> I was once told silver oxide is a conductor and copper oxide is not, so
>>> that's
>>> an advantages in using silver. I've never looked in the professional
>>> literature
>>> to see if that is true - it may be a lot of rubbish.
>>>
>>> dave
>>
>> Agree, silver plating is strictly for show up to some unknown frequency.
>>
>> Ive been running a 2M flat plate line 3CX1000A7 for over 25 years and its
>> still running the same 1500W with the same tube. Use is limited to contests
>> and interesting band openings.
>>
>> A 4CX250B cavity for 440 ran 250W out when I built it 30 years ago for FM
>> use in contests, it doesnt have many hours on it. I checked it an hour ago
>> and its still the same. Construction is from copper water pipe.
>>
>> The biggest problem I see in amps is poor RF connections causing crystalized
>> solder joints and increased RF resistance with the copper or silver coil and
>> connecting wiring getting the blame. If youre going to run real power then
>> silver solder as well as bolt together anything that can be bolted. Dont run
>> #14 or 16 wire to the bandswitch, especially 20M and above. At a minimum use
>> silver bearing solder for all RF connections.
>>
>> Carl
>> KM1H
>>
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