Dr. Barry L. Ornitz wrote:

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.

And, when tightened threads *are* necessary for electrical contact, oil
or light grease often improves conductivity. Thread pressure is adequate
to squeeze the lubricant out from the contact areas, allowing good
metallic contact. And it prevents oxidation or other corrosion of the
contact surfaces when the contacts are moved or vibrate by excluding
air. This holds true for all contacts properly designed to wipe and
contact with sufficient pressure. Quite a few people incorrectly
attribute this improvement to conductivity or some mystical property of
the lubricant, but its real trick is simply to exclude air.

Roy Lewallen, W7EL