Topband: Verifying integrity of 75 ohm coax.

[HAROLD SMITH JR]

Hi Jim and All,

I had been working in Medical Electronics 25+ years... Now retired for over 20 years. 

Silicone Grease was and is still used on all high voltage connections to the X-Ray tube. The cathode lead 
had the high voltage and the filament voltage. It never changed any of the filament current settings.
The X-Ray tube current is varied by adjusting the filament current with a constant anode voltage. 
The filament current is about 4 to 7 amps.
73 Price W0RI



> non-conducting grease on, e.g., the center terminal of an N-connector or

> PL259 seems like asking for trouble.
> 73,
> Jim W8ZR
>

Years ago, working in telephone plant for AT&T Long Lines, I had that same
intuitive "oh really, how can that possibly work" gut response to the Bell
System Practices mandated procedure of slathering up massive mating
electrical surfaces with a particular grease, about axle grease
consistency, much thicker consistency than the automotive silicon
recommended in this thread. The connection when active would carry almost
5000 amps 24/7.

My intuitive mind viewed the grease as an impediment, an insulator. But the
mate was accomplished with four bolts set to something like 50 ft. pounds
of torque. It was then retorqued on interval until it quit loosening. I was
always surprised that an ordinary voltmeter across the connection would
never deflect the needle. Took a special taut band meter to measure the
normal and acceptable millivolts level of voltage drop.

The real issue was to never, ever, let air and any airborne contaminants
(including water) get to the surfaces. Clean, slather, mate, torque,
retorque and forget it. Occasionally we would remove one that had been
untouched for decades and still no drop across the connection.

Grease "inside" connections is just another circumstance where the
intuitive sometimes doesn't serve us so well.

73, Guy.
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