Yes, of corse twisted pairs can handle fast signals. Gigabit Ethernet over cat-5 cable is a good example.
What I meant when I wrote the below is that a bare t-bolt PPS output can't drive 100 feet of cat-5 cable when the far end is connected to to typical 74LSxxx t/l chip. The pulse get smeared. Yes, you could make it work easy enough. Place some RS-422 transceivers on each end and it would work just fine. But what I said is the t-bolt is not able to drive the cable. I tried it using a spare pair in a cat-5 cable that was already installed in the walls and up two floor. It was very unreliable. On Fri, Jul 20, 2012 at 4:31 PM, Hal Murray <hmur...@megapathdsl.net> wrote: > > (From a month ago.) > > albertson.ch...@gmail.com said: >> Take my word for it, the T-Bolt is not able to drive a 100 foot long twisted >> pair cable > > I don't think that's quite the right way to phrase it. > > What type of twisted pair were you using and/or what sort of setup did you > try? How well did it work and/or what were you expecting? > > Yes, you may get much better results if you use differential > drivers/receivers. But that's if you have common mode problems. > > ----------- > > I remember, many years ago, when I got an interesting lesson in this area. > The difference between junk twisted pair and good stuff was impressive. > > We were installing a T microwave link. On T1, a 1 is a pulse, a 0 is an > absence of a pulse during a bit slot. Pulses alternate polarity to keep a DC > balance. T1 is 1.544 megabits/second or 647 ns per bit. I don't remember > the details, but the ballpark is a 200 ns pulse has to get through. So the > rise time has to be in the ballpark of 20-50 ns. > > We had to go a few hundred feet. My first try with a spool of whatever I > found in the lab was a joke. The spool of good stuff that we ordered worked > fine. I'm pretty sure the good-stuff was Belden Datalene but, again, it was > a long time ago and I don't remember any details. (I wonder if the cable is > still there.) > > Does anybody have a good URL on lossy transmission lines? Is there any > obvious reason why twisted pairs should be different from coax? > > ----------- > > Does anybody know what the PPS driver in a TBolt is? I assume it's a typical > CMOS logic family. Is it one section or several in parallel? What > chip/family? ... > > It clamps reflections. In any case, it's not linear. > > ---------- > > I collected some cable and tried a few experiments. > > Theses are all nominally 100 feet long. I didn't measure any of the lengths. > > Coax: > http://www.megapathdsl.net/~hmurray/time-nuts/coax/Coax-20ns.png > http://www.megapathdsl.net/~hmurray/time-nuts/coax/Coax-100ns.png > http://www.megapathdsl.net/~hmurray/time-nuts/coax/Coax-1us.png > > Twisted Pair: > http://www.megapathdsl.net/~hmurray/time-nuts/coax/TP-20ns.png > http://www.megapathdsl.net/~hmurray/time-nuts/coax/TP-100ns.png > http://www.megapathdsl.net/~hmurray/time-nuts/coax/TP-1us.png > > The Belden 8723 is 52 ohms. (I probably used 50 ohms.) The other twisted > pairs are 100 ohms. > > I'll have to try harder to find some really-junky twisted pair. > > The scope is the standard Rigol 100 MHz. I had to work a bit on the setup to > get clean pictures. An early attempt with several feet of clipleads and such > added a lot of garbage. > > The difference between 3 ft of brand-X RG-58 and 1 ft of good RG-58 from the > TBolt to the scope is easy to see. The brand-X isn't 50 ohms. > > > > -- > These are my opinions. I hate spam. > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. -- Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.