BNC Connector/Cable Suggestion
LVTTL is low voltage TTL (and TTL is transistor-transistor logic).  LVTTL runs at 3.3V instead of the usual 5V.  The "5V tolerant" means it doesn't mind being fed conventional 5V TTL if needed.

You won't find a 1kΩ BNC plug.  Don't worry about it.  It's just an "arm" signal, so impedance matching won't be critical.