Moczik Gabor put forth on 3/28/2011 12:01 AM: > Stan Hoeppner wrote: >> We bought DB25 plugs in bags of 100, and used spooled CAT5 as the noise >> rejection is many times that of CAT3, allowing greater distances across >> sprawling warehouses. > > RS-232 uses single-ended signaling and requires shielded cable, twisted > pair doesn't help either.
Interesting to see you state this, considering the experience of many IT folk stuck supporting legacy serial terminals and printers proves the opposite to be true. Back in 1996/7 I worked for such a legacy equipment using company, a chemical producer in St. Louis. We were routinely (weekly) making 200+ ft. CAT5 UTP (24 AWG solid plenum cable) runs across warehouses and production buildings. The connections were between RS232 Wyse terminals, thermal label printers, and ethernet terminal servers at 9600 bps, using 3 conductors, one twisted pair (orange/white-orange) and one single conductor of another pair (green) for ground. We could reliably run 115,200 bps on runs up to 50 ft. using CAT5 UTP. The cables distances we routinely achieved were obviously many times the RS232 spec maximums. > The common-mode noise rejection of twisted > pair only works if the signals connected to a balanced input receiver. Twisted pair cabled achieves its rejection performance against EMI/RFI simply due to its design, not whether the signal is balanced or not. If any non-negligible length of the cable is in proximity to a noise source, having twisted conductors minimizes the potential pick up area of any one conductor. The single largest user of twisted pair cable, its inventor and progenitor actually, was AT&T (the old monopoly AT&T), now known as many different companies after the 1980s breakup of the AT&T monpoly and the creation of the "baby Bells", now known as Verizon et al. CAT1 and CAT3 UTP have been used for telephones for more than 6 decades, and I'm pretty sure everyone knows telephones don't use balanced signals. You should read about the history of UTP cabling. It's pretty interesting, for a geek anyway. -- Stan -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected] Archive: http://lists.debian.org/[email protected]
