The resistance will be the square root of the resistivity of the conductor.
So if the resistivity increases by a factor of 1.1 the resistance will
increase by
a factor of 1.05 assuming the thickness or diameter of the conductor is
much greater
than the skin depth.
This is easy to see since the skin depth is directly proportional to
the square root of
resistivity.
73
Bill wa4lav
At 04:50 PM 10/4/2010 -0400, Steve Thompson wrote:
>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@onetel.net>
> >> To:<amps@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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> >>
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> >
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