I've more than some doubt if available copper is really a
better conductor than silver plating.
Under my eyes, a big power commercial VHF/FM amplifier
prototype was on test and the tuned line, a bare copper
machined from a single piece, heated quite a lot. The same
line, after silver plating, didn't develop any abnormal heating.
I can report a brand new (bright, shining) copper VHF cavity,
part of a duplexer, had a certain bandwidth and attenuation.
The same cavity was then silver plated. The bandwidth
decreased toghether the attenuation.
The same was done in a similar cavity but UHF, the difference
was markedly bigger.
73,
Mauri I4JMY
-----Messaggio Originale-----
Da: Ian White, G3SEK <G3SEK@ifwtech.demon.co.uk>
A: <amps@contesting.com>
Data invio: sabato 18 settembre 1999 17.54
Oggetto: Re: [AMPS] Silver Plating question
>
> Norman Hockler wrote:
> >
> >Guys...
> >
> >The advantage in silver plating is, of course, the lowering of
resistance
> >caused by the skin effect, and as we know all the current will travel on
> >the surface of the cavity. The silver plating does not have to be very
> >thick to get the desired effect of the additional few watts this will
afford.
> >
> >There are a number of low cost silver plating kits available. I used one
> >for my 8877 amp that worked fine. Cost me $12.
>
> It's unlikely that you would see much - if any - improvement in
> efficiency in a typical VHF "cavity" amp.
>
> The places where conductivity is the most important are the parts
> carrying the highest current density (amperes per square inch). This
> typically means the tuned line, which is generally made of copper
> anyway. Pure copper actually has a higher conductivity than silver, and
> copper has a higher surface conductivity for RF if the surface is kept
> clean.
>
> The story that "silver is good because silver oxide is a good conductor"
> is largely a myth. When silver tarnishes, it usually forms silver
> sulphide, which is a pretty lousy conductor. In order to keep silver-
> plated surfaces conducting RF at peak efficiency you still have to clean
> it.
>
> The only significant advantage of silver plating over bare copper is for
> use in situations where you cannot conveniently clean it - for example,
> I use silver-plated conductors in sleeve balun assemblies that live
> outside, and would have to be unsoldered to clean them. But in a VHF
> amplifier, you only need to take the bare copper tuned line out to clean
> it.
>
> The other problem with silver plating is that it has to be done right,
> or else the result will be worse than copper. Decorative silver plate
> contains some nickel, and its RF conductivity is significantly worse
> than pure silver. If you have the plating done for you, you can specify
> pure silver, but you can't guarantee that they really did empty the
> tanks and change the chemicals just for you. Do-it-yourself silver
> plating gives you more control over the composition, but less control
> over the crystal structure of the metal that's laid down - which can
> greatly affect the conductivity.
>
> The aluminum box parts of the cavity are no problem. Generally they
> carry a lower current density than the tuned line, simply because there
> are more square inches involved. Since losses are proportional to
> (current density) squared, the losses are much lower.
>
> I'd recommend using bare copper and occasional elbow-grease, and keep
> the silver in your pocket.
>
> 73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
> 'In Practice' columnist for RadCom (RSGB)
> http://www.ifwtech.demon.co.uk/g3sek
>
> --
> FAQ on WWW: http://www.contesting.com/ampsfaq.html
> Submissions: amps@contesting.com
> Administrative requests: amps-REQUEST@contesting.com
> Problems: owner-amps@contesting.com
> Search: http://www.contesting.com/km9p/search.htm
>
--
FAQ on WWW: http://www.contesting.com/ampsfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|