On 25 May 2010 02:15, Stanley Reynolds <[email protected]> wrote: > My fix for ground loops was to cut the shield at the terminal end and leave > it connected at the computer end, worked most of the time. Other fixes were > short-hall modems, isolation transformer for the terminal, and last fiber > optic drivers with fiber optic cable.
Like what I said, so that's at least two votes now :) Steve > Stanley > > > > ----- Original Message ---- > From: Robert Benward <[email protected]> > To: Discussion of precise time and frequency measurement <[email protected]> > Sent: Mon, May 24, 2010 7:20:32 AM > Subject: Re: [time-nuts] Z3805 utility, Was: AW: (no subject) > > Steve, > If you are worried about ground loops you should be using RS-422. I can > almost guarantee you that pin 7 is attached to > the PCB ground plane which in turn is connected to chassis. Hopefully > everyone is plugged into the same outlet and the > RS-232 signaling levels are sufficient to overcome the common mode noise. > > Bob > > > ----- Original Message ----- > From: "Steve Rooke" <[email protected]> > To: "Discussion of precise time and frequency measurement" > <[email protected]> > Sent: Monday, May 24, 2010 1:40 AM > Subject: Re: [time-nuts] Z3805 utility, Was: AW: (no subject) > > > On 24 May 2010 15:22, Robert Benward <[email protected]> wrote: >> My experience with the term "straight through" is that I've seen RS-232 >> cable that have the ground pin connected to the shell. In a "straight >> through" the pins are one to one and the only thing connected to the shell >> would be the shield if one is available. > > There is a difference between the signal ground on pin 7 and the shell > which forms a shield around the connector and may be connected to a > shield on the cable if there is one. You have to be careful with this > sort of setup though as earth loops can be caused by connecting the > chassis earth on two bits of equipment via the cable shield. That's > why pin 7 is the signalling earth and it really should not be > connected to earth at either end, IE. attempts at doing 2 wire > signalling et al. > > Steve > >> Bob >> >> ----- Original Message ----- From: "Bob Camp" <[email protected]> >> To: "Discussion of precise time and frequency measurement" >> <[email protected]> >> Sent: Sunday, May 23, 2010 9:21 PM >> Subject: Re: [time-nuts] Z3805 utility, Was: AW: (no subject) >> >> >>> Hi >>> >>> Long ago I decided to go with the terms "straight" and "null modem" for >>> the cables I use. NM and ST are easy to mark and hard to confuse. >>> >>> Bob >>> >>> >>> On May 23, 2010, at 8:58 PM, jimlux wrote: >>> >>>> Stanley Reynolds wrote: >>>> >>>>> <snip> >>>>> Dec computers / terminal servers were as I described, but many brands >>>>> were different. Still have a BOB aka break out box with LEDs to >>>>> indicate levels, matching transmit and receive is easy, getting the >>>>> hardware flow control / signaling right was a little more difficult. >>>>> straight cable = pin to pin >>>>> crossed cable = null modem = swapped pins >>>>> The phrase "null modem" comes from no modems or the configuration >>>>> that allows two singular ports to be connected, this cable would >>>>> cross the receive and transmit pins, and some would call it a cross >>>>> over cable. A null modem cable would be used to connect two computers >>>>> together and a program like kermit used to transfer files. >>>> >>>> >>>> Yep.. DTE cable to DCE communications medium(phoneline) DCE to DTE >>>> DCE == Modem (e.g. a Bell 202 or 212, for instance) >>>> >>>> There were the flow control (RTS/CTS) used to turn around a half duplex >>>> link. And, there are also the secondary transmit and receive (for a low >>>> rate reverse channel). If you were receiving data from the link (DCE), >>>> you'd assert RTS, and when the modem had switched, it would tell you CTS, >>>> and off you'd go. (fancy modems used the reverse channel to send the >>>> request to the far end, which would acknowledge... others just use a fixed >>>> time delay) There are also pins for the clock (since some of these modems >>>> were used on synchronous data links). >>>> >>>> the "crossover" occured in the DCE to DCE link (that is, you'd transmit >>>> from one DCE to the other DCE's receiver)... >>>> >>>> the nominal cable between DTE and DCE was straight through. With no real >>>> convention on male/female.. most devices had female sockets, and the cables >>>> usually were male male plugs. IBM PCs had male on the chassis for DTE, as >>>> did some PDT-110 (VT-100/LSI-11 smart terminals), but most other terminals >>>> (the LSI ADM-x, Hazeltines, etc.) all seemed to have female, as did the TI >>>> 800 series printer/terminals. >>>> >>>> So, a "null modem" was a cable that emulated the DCE to DCE connection.. >>>> >>>> there are/were various strategies on how sophisticated the reverse is.. >>>> do you also send the secondary channel? What about clocks? Most folks >>>> ignored all that and used RTS/CTS >>>> >>>> Or you strap RTS to CTS on your side, the other side does the same. >>>> >>>> >>>> >>>> >>>> >>>>> I think the phrase "standard cable" which could be null or straight >>>>> depending on the use is the confusing part. >>>>> Phone cables RJ11 and RJ45 swap the wires which is standard. Network >>>>> cables match the wires with the same color always on the right which >>>>> is standard. But even when a phone cable is standard it is not >>>>> interchangeable with a standard network cable. Again we have a need >>>>> for cross as well as straight network cables. >>>> >>>> >>>> And, to make things worse, there are different "pair" arrangements. >>>> >>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- [email protected] >>>> To unsubscribe, go to >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> and follow the instructions there. >>>> >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > > > -- > Steve Rooke - ZL3TUV & G8KVD > A man with one clock knows what time it is; > A man with two clocks is never quite sure. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > -- Steve Rooke - ZL3TUV & G8KVD A man with one clock knows what time it is; A man with two clocks is never quite sure. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
