George White wrote in a message to Mike Bilow:
MB>The principal benefit to gold plate is immunity from
MB>corrosion.  This is essentially unimportant in networking,
MB>where currents are negligible.  In audio, for example, you
MB>might commonly pass tens of amps to a speaker, and
MB>corrosion would form a high-resistance spot which would
MB>heat up.
 GW> From my experience in designing high reliability
 GW> engine/transmission control systems for military
 GW> applications (everything from milivolt to several amps on
 GW> the connectors), the advantage of gold is indeed immunity to
 GW> corrosion, but only during storage! Once a properly designed
 GW> connector has been mated the existance of the gold plate
 GW> becomes irrelevant.
Keep in mind that we are not necessarily talking about something that weighs 
only a few grams and which is protected by a plastic shell, which is the 
usual model in automotive electronics.  In a BNC connector used for 
networking, the parts are often press-fit and can wobble or rotate freely, 
often each time the computer or cable is moved or bumped.  There's no strain 
relief on BNC, and even the bayonet locking pins comprise part of the live 
electrical connection! The practical effect is that the connector is always 
exposed to corrosion as if it was still in storage.
 GW> You have the benefit of gold against current the wrong way
 GW> round! The higher the current, the less relevant the gold
 GW> plate becomes (when a high power connector is mated the two
 GW> mateing parts should distort and cut through the gold plate
 GW> with the working contact being between the underlying
 GW> connector materials)
Well, yes and no.  Yes, an impedance discontinuity can do more damage to a 
milliamp signal in terms of noise.  No, it is usually a much bigger problem 
if you pass tens of amps through an impedance discontinuity -- because you 
might start a fire.
The gold plate is not cut away on BNC (or most other) systems.  Gold is an 
excellent conductor, and there is no reason to let it be cut away.
MB>Connectors of proper design should not introduce impedance 
scontinuities.
 GW> Hear hear. But how many can verify if the BNC connector is
 GW> 50 or 75 ohms? (and even if they can, how many bother?)
The center conductor is a different thickness.  It is very obvious if you 
have ever seen both types next to each other at the same time for comparison.
 
-- Mike
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