Rick Frazier wrote:
Take two bare copper wires (don't clean them), twist together and leave
in the weather for a few weeks. If you get any sort of rain and some
decent sun, before long you will have a "high ohmic" connection. The
more oxidation between the two wires at the point of contact, the higher
the resistance. This can be detrimental, especially if you're using low
power (QRP). On the other hand, if you have an amplifier and transmit
through this sort of poor connection it can actually get worse, and you
can end up with variable swr, which most amplifiers don't like....

Typically, any clean, tight joint will be fine for awhile, longer if
protected, and longer yet if soldered before you protect it.....

--Rick AH7H

What you need to do is keep air and moisture from between the wires,
once you've put them together with enough pressure to break through the
surface oxide and make good metal-metal contact. That's how wire nuts
and clamp and crimp type connections remain reliable for a long time. Of
course, soldering accomplishes this too.

Roy Lewallen, W7EL