Topband: Verifying integrity of 75 ohm coax. ( silicone grease)

[Tom W8JI]

>> Very soon afterwards (a few weeks instead of perhaps a year), the
>> operator called me over to show me the problem with that switch. I know
>> what I saw, and I am convinced that it is abrasive. That grease 
>> accelerated
>> the failure of that switch by a tremendous amount.
>
>
>
> This is very interesting and something I also discovered and never 
> reasoned why, I have used Potable silicone grease inside PL-259 coax 
> connectors and never had a problem, however, when I have used the same 
> grease inside the rotary preset switch for my Prosistel rotator controller 
> box it destroyed the switch in a couple of months, now I know why.

Actually, that flies in the face of everything published about typical 
silicone dielectric greases.

What is often stated and documented and applies to this is that silicone 
grease will form silicone-carbide when subjected to arcs.  Silicone-carbide 
is a great abrasive. This is why you cannot use silicone grease in contacts 
that arc when switched.

Silicone carbide:

http://www.3m.com/product/information/Waterproof-Silicone-Carbide-Sheet.html

Let's not create a new theory that silicone grease is abrasive, when nothing 
supports that theory. Silicone grease is commonly used to lubricate things 
that rubs and slide, including switch contacts and potentiometers. It is 
used to reduce fretting in sliding connectors that vibrate. It is clearly 
not abrasive unless carburized.

If a contact **sparks**, it normally should be left dry or lubricated with 
something that does not carburize. The only exception would be if a 
manufacturer says otherwise.

73 Tom