C
It certainly can. At certain distances and lengths, it can prevent data transfer entirely. But the characteristic impedance does not depend on the wire being twisted, parallel transmission lines do work and are used e.g. the common TV twinlead. The twisting is for better noise immunity.
It may be that the cable is close enough, the 120 ohms is after all, a rather ballpark number, often completely ignored and things somehow work. In fact, I've seen many setups that shouldn't work, work. But then some bogus setups absolutely refuse to work, even a little. But done properly, they almost always work and very well. I had to redo an entire hospital once (not RS485) because of the difference between STP and UTP. The maintenance guys figured that shielded would be better. The cost of the proper wire for RS485 is so low (compared to other industrial networks) I just can't see not using it.
Regards
cww
It may be that the cable is close enough, the 120 ohms is after all, a rather ballpark number, often completely ignored and things somehow work. In fact, I've seen many setups that shouldn't work, work. But then some bogus setups absolutely refuse to work, even a little. But done properly, they almost always work and very well. I had to redo an entire hospital once (not RS485) because of the difference between STP and UTP. The maintenance guys figured that shielded would be better. The cost of the proper wire for RS485 is so low (compared to other industrial networks) I just can't see not using it.
Regards
cww
