Just like the tittle say. Could water or heavy mosture stop or degrade a audio and video signal in a coax cable? If so how is it possible since water is a conductor? I know water would stop a signal through fiber but what about a copper conductor?

 

The water shorts the signal to the shield.

Funny story: A neighbor drives up and says the radio in his pickup truck isn't working.
Rain happened recently and he had a wire coat hanger stuck in the hole where his antenna was broken off.
I lifted the coat hanger, blew in the hole, and put the coat hanger back.
The radio resumed working and he thougth I was a genius.

Water shorts out coaxial conductors.

 

Yep. If there is any impurities in the water (quite common) then it is a conductor, and can degrade by shorting out the signal.

Either a compromised insulator, or an egress at a connection point would allow the water to enter. If a solid cable is laying in a puddle then it should be OK.

 

The short answer is yes and will affect the capacitance and impedence of thecable Even worse it will eventually work its way both up and down the cable and cause electrolysis in the presence of a voltage supply. it may eventually munch your electronics if it gets that far.

 

So the short would happen at the connector itself? Most coax have a dielectric foam between the shield and the conductor.

 

Dielectric is to give the cable a specific capacitance and impedence 50Ω & 75Ω being two very common examples. The propagation of the signal along the cable is dependent on this.

If water enters a cable then the dialectric constant is going to change and by extension the capacitance of the cable.

It is a little complicated but there is much more info here - well worth reading
http://en.wikipedia.org/wiki/Telegrapher's_equation

 

OK I thought the dielectric foam was only use as an insulator.