[time-nuts] Z3805 utility, Was: AW: (no subject)

Mon May 24 14:20:14 UTC 2010

On 25 May 2010 02:15, Stanley Reynolds <stanley_reynolds at yahoo.com> 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 <rbenward at verizon.net>
> To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
> 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" <sar10538 at gmail.com>
> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
> 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 <rbenward at verizon.net> 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" <lists at rtty.us>
>> To: "Discussion of precise time and frequency measurement"
>> <time-nuts at febo.com>
>> 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.
>>>>
>>>>
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>>>
>>>
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>
>
>
> --
> Steve Rooke - ZL3TUV & G8KVD
> A man with one clock knows what time it is;
> A man with two clocks is never quite sure.
>
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>
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-- 
Steve Rooke - ZL3TUV & G8KVD
A man with one clock knows what time it is;
A man with two clocks is never quite sure.