simnet@ssc-vax.UUCP (Mark R Poulson) (10/27/90)
Since I don't know of any sci.phones group I thought I would try sci.electronics... I want to string some telephone extension cables that will go a rather long distance (~100 feet). With these cables, I thought I'd string some others for future use (alarm, RS232, ...). For the other cables I want to use shielded twisted pair, but telephones are usually done with unshielded cable. I would really like to buy one cable with multiple pairs, but I can't find any with both shielded and unshieled twisted pairs. So my question is: can I use shielded twisted pair for telephone circuits or do they have undesireable side effects? Thanks, Mark ...uw-beaver!ssc-bee!simnet
segal@motcid.UUCP (Gary Segal) (10/28/90)
simnet@ssc-vax.UUCP (Mark R Poulson) writes: >Since I don't know of any sci.phones group I thought I would try >sci.electronics... >I want to string some telephone extension cables that will go a rather long >distance (~100 feet). With these cables, I thought I'd string some others for >future use (alarm, RS232, ...). For the other cables I want to use shielded >twisted pair, but telephones are usually done with unshielded cable. I would >really like to buy one cable with multiple pairs, but I can't find any with >both shielded and unshieled twisted pairs. >So my question is: can I use shielded twisted pair for telephone circuits >or do they have undesireable side effects? You may have some problems running RS232 at distances over 50 feet. Especially if you are planning on using faster data rates (9600bps or more). The problem with longer cable runs is that the capacitance of the cable does not allow the signal to change as fast as you want it. If you have a problem, you'll want to get a pair of short-haul modems, which are designed specfically for this type of installation. As far as you telephone lines go, using shielded twisted pair will have DESIREABLE side effects. If you are running multiple lines, twisted pair will reduce if not eliminate the chance of cross talk. Sheilding only helps to reduce the chance of noise entering the cable, which seems very likely if you are going to run RS232 in the same cable. Of course, you must be very carefull about your sheild grounds - in most cases, you only want to ground one end of the cable sheild. Whatever you do, don't run ANY current through the sheild. -- Gary Segal ...!uunet!motcid!segal +1-708-632-2354 Motorola INC., 1501 W. Shure Drive, Arlington Heights IL, 60004 The opinions expressed above are those of the author, and do not consititue the opinions of Motorola INC.