27 Sep
2004
27 Sep
'04
3:37 p.m.
On Sun, 2004-09-26 at 16:25, Ted.Harding@nessie.mcc.ac.uk wrote:
Hi Folks,
Your solution will create lots of impeadance mis-matches in the cable...
The cable is 50ohms, and when two pieces are joined together with a T piece, the card driving them sees 25 ohms ( = two 50s in paralell), but it is designed to drive 25 ohm load.
If you connect a third piece of coax to a t-piece, the end of this piece now sees the 25 ohms presented by the other two in parallel (note this applies to all of the three cables). The 25 ohm mismatch will create reflections and will screw up the collision detection and could in exceptional cases prevent communications between some nodes.
Don't Do It
Peter