(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.