🚀 go-pugleaf

In <sreyas5rvgt.fsf@ptavv.es.net>, Kevin Oberman <oberman@es.net> writes:
>> With 10Base2 proper impedance matching is critical to prevent reflections 
>> -- which cause errors and false collisions.  However, for reasonably small
>> nets you should be able to use 75 ohm cable **IF** you use 75 ohm 
>> terminators.  The drivers and receivers should be able to tolerate the 
>> difference in current and voltage.
>
>This is not correct. Even if you use 75 ohm coax, you MUST terminate
>with 50 ohm terminators. On coax the collision detection works on DC
>signaling which is sourced as a current. If the DC resistance of the
>cable is wrong (37.5 ohms vs. 25 ohms), collision detection breaks.

Yeah, I'd forgotten about how Ethernet does collision detection.  Best bet
might be to split the difference and go with terminators in the 65-ohm 
region.  But really, folk, 10Base2 is a dead-end technology.  The far 
better strategy would be to pull in Cat-5 twisted pair cable and run 
10BaseT.  Pulling new cable sometimes takes creativity, but there's 
(almost) always a way.

Dan Hicks
Hey!!  My advice is free -- take it for what it's worth!
http://www.millcomm.com/~danhicks