I remember my NCR Tower had a BNC plug on the back
which was wired into the
PSU as part of the power-fail circuitry - I suspect that if wired up to an
Ethernet then interesting things would happen...
A number of HP devices have a BNC conenctor as a 5V power output to ru na
logic probe or external add-ons. My HP1630D logic analyser has one o nthe
bnck pannel to power probe interedaces. The 59403 HPIB-RS232 interface
has one on the back to pwoer a logic probe for testing, my
Multiprogramemr has one inside the front door for a similar purpose. I am
told some HP logic probles had a BNC plug on the cable specifically to
plug into such a connector.
And of course BNC connectors have been used ro the RF output of smallish
radio transmitters. I suspect applyig na few watts of RF to an ethernet
cable could be 'interesting'.
Moral : Do not connect random BNCs together...
-tony