[AMPS] Silver Plating in Commercial Products

[Jon Ogden]

Hi all,

I found out why the company I sell for silver plates their cavity filters.

The filters are hogged out of a block of aluminum.  Aluminum stinks as an 
RF conductor as the losses are too high.  Therefore, they plate the 
aluminum with silver in order to improve the conductivity and Q of the 
parts.  In some cases, if a customer wants to save money and doesn't need 
the super low loss performance, we will sell unplated filters.

The silver plating gives about a 50% better improvement in loss over 
unplated.  For example, a 6 pole cavity filter, unplated may have an 
insertion loss of 1 to 1.2 dB.  After plating, that loss is typically 
less than 0.5 dB.

Now, comparing silver to copper.  There is not much difference in pure RF 
performance.  Yeah, silver is a little better but not much.  So why not 
use copper filters instead of aluminum?  The reason has to do with 
corrosion and intermodulation distortion.  Back in the early days of 
cellular, Allen Telecom held the market in cellular cavity filters.  All 
of them were copper.  However, in the UK, some of the operators started 
having problems.  The company I sell for (based in the UK) did studies 
and determined that the problems in the base stations were due to the 
copper filters.  The copper oxide was causing passive intermod problems.  
Silver is far better than copper in preventing the generation of passive 
IM.  And silver tarnish (oxide, sulphide, whatever) while not as 
conductive as untarnished silver is a better conductor than copper oxide.

So in general the switch was made to silver plated aluminum cavities.  
Additionally, I think aluminum might be cheaper and easier to machine 
than copper, but I am not speaking with any authority there.  It's a 
guess.  It also might weigh less.

And nowdays in order to prevent tarnish of the silver, they coat the 
inside of their cavities with some sort of coating that prevents tarnish 
as well.

Anyhow, then getting back to the original question:  Should I silver 
plate my copper cavity in a UHF amplifier?  Probably not worth the hassle 
and cost.  Copper is probably fine.

73,

Jon
KE9NA


--------------------------------------------------------------------------
The Second Amendment is NOT about duck hunting!


Jon Ogden

jono@enteract.com
www.qsl.net/ke9na

"A life lived in fear is a life half lived."


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