[Premium-Rx] Cleaning RF cavities.

[Richard Reich]

Hello List.
I have been involved in refurbishing high-power television transmitter, and
microwave link, cavities - and the practices used here may be of help to others.
The cavities and sliding fingers are usually silver plated. Do not be tempted to
use any sort of abrasive paper, or metal polish. Quite apart from the damaging
abbrasive nature - the polish always leaves behind some sort of residue which
gives more problems later. For cleaning we used a silver replacement solution
called "Silver Dip' made by Goddards - and the items are dipped/immersed in it.
Simply put, this re-converts the silver oxide back into silver - like
currentless electro-plating. Failing the use of Silver Dip, just clean
thoroughly and vigorously with very mild detergent and water using plenty of
elbow - then dry out in an oven system. Where you have corrosion - this will
need to be abraded, polished, and re-plated using Silver Dip. One common problem
is wear on cavity fingers - if there are flats appearing, problems are in the
wings. The cavities themselves are never lubricated with anything. One of the
worst lubricants in electronics is WD40 - it dries to form an insulating film -
and will certainly stuff the efficiency of a cavity, and is very difficult to
remove afterwards. One safety note - spring fingers are usually made of
Berillium Copper - whether silver plated or not - the fine copper dust release
through wear is a carcenogen - so take care. Hope this helps.
***************************************************************
Richard Reich    
Principal Engineer Hardware
SAAT Technology Ltd
Web: http://www.saatt.co.uk

DDI: +44(0)1420 545388
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