>
>I've more than some doubt if available copper is really a
>better conductor than silver plating.
>
? Indeed, Mauri. Some people apparently open their mouth Before they
open the appropriate books.
>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
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>>
>
>
>
>
>--
>FAQ on WWW: http://www.contesting.com/ampsfaq.html
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>
- Rich..., 805.386.3734, www.vcnet.com/measures.
--
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