"JB" wrote in message
...

At one time I thought silicone grease would save wear on N
connectors until I used the spray on wattmeter slugs and found it
completely insulated the shell contact. I since found it caused
an SWR hump on N connectors even if it were just a spot on the
threads.

I could see where the thin silicone coating might be an insulator to the
low voltages from the wattmeter slubs, but I find the second statement
exceptionally hard to believe. In type N (and even BNC) connectors, the
threads (or the bayonet connection) are not in the RF path. Look close at
either type of male connector and note that there is a coaxial shield
around the center pin. This shield presses against the inside wall of the
jack providing a continuation of the coaxial line. The threads (or the
bayonet connection) merely provides a sturdy mechanical connection. This
what gives the type N and BNC connectors a constant impedance, and what
makes them far superior to UHF connectors. It also allows the use of a
rubber washer to make the connector waterproof.

In one of my instrumentation applications, I had to use N connectors made
of 304 stainless for corrosion resistance and high temperatures. Ceramic
and glass insulation was used within the connectors. The female jacks were
welded in place and rated to withstand pressures of up to 100 PSIG.
Stainless is quite bad about galling, and these connectors cost plenty, so
a silver paste was used to lubricate the threads. One day, I had to make
an "emergency" repair in the field and did not have the silver paste; so I
used PTFE thread seal tape instead. Going back to my lab, I tested a few
connectors with the thread seal tape using a Tek 1502 time domain
reflectometer. Even with several layers of PTFE tape, I was unable to see
any difference in the impedance through the connector. Since the
application was always less than 200°C, we quit using the silver paste.

--
73, Dr. Barry L. Ornitz WA4VZQ

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