Interface two Ethernet (10 Base) devices without 4 twisted pairs cable (Common ethernet cable) and 10 Base-T Filter
Try this application note from Micrel.  It's their app note, so they promote their devices that they've tested it with, but I'd be very surprised if it doesn't work on pretty much any Ethernet PHY - they're all interoperable.

edit: The app note tells you exactly how to wire two PHY's back to back, including if one or both of them are "current mode", or "designed to interface to a transformer".