cable tester

On Sat, 18 Apr 2020 20:43:47 -0400, "Tom Del Rosso"
<fizzbintuesday@that-google-mail-domain.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sat, 18 Apr 2020 08:03:59 -0400, "Tom Del Rosso"
fizzbintuesday@that-google-mail-domain.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sat, 18 Apr 2020 15:55:00 +1000, Clifford Heath
no.spam@please.net> wrote:

It doesn't tell you when you have mixed-up pairs, like in an
Ethernet cable where you have a blue/orange pair and an
orange/blue pair.

I think modern Ethernet doesn't care.

What it doesn't care about is when a twisted pair goes from pins 1-2
to pins 3-6 at the other end, and 3-6 to 1-2.




Don't do that, and don't expect any simple tester to report that. It
would have to accurately measure 3-terminal mutual capacitances or
something. UTP would be especially tricky. Are there affordable
testers for that?

What I described is a simple crossover cable. (Xmit pair to Rcv pair and
Rcv to Xmit.) Any cheap tester can report that. I have a $5 one that
does. But it can't detect split pairs that Cliff described.

You must be describing something else but what?
Click to expand...

I was thinking Cat5/6 ethernet cable, with three pairs. Same problem
of detecting switched wires that preserve DC continuity.


If a cable in your network doesn't work for whatever reason, throw it
away.

I wonder when such a wiring error would really trash ethernet packets.
For some lengths and rates, it might not.

I saw a Cisco IP phone (the top brand after all) that would not connect
with a single intermittent wire in the brown pair, which is an optional
pair. It tried to connect at 1 Gbps with 4 pairs and when it failed it
would not revert to 100 Mbps on 2 pairs. So I disconnected the blue and
brown pairs and it worked fine with only the other two.
Click to expand...

--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard
 
jlarkin@highlandsniptechnology.com wrote:
On Sat, 18 Apr 2020 18:49:57 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 18 Apr 2020 20:43:47 -0400, "Tom Del Rosso"
fizzbintuesday@that-google-mail-domain.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sat, 18 Apr 2020 08:03:59 -0400, "Tom Del Rosso"
fizzbintuesday@that-google-mail-domain.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sat, 18 Apr 2020 15:55:00 +1000, Clifford Heath
no.spam@please.net> wrote:

It doesn't tell you when you have mixed-up pairs, like in an
Ethernet cable where you have a blue/orange pair and an
orange/blue pair.

I think modern Ethernet doesn't care.

What it doesn't care about is when a twisted pair goes from pins
1-2 to pins 3-6 at the other end, and 3-6 to 1-2.




Don't do that, and don't expect any simple tester to report that.
It would have to accurately measure 3-terminal mutual capacitances
or something. UTP would be especially tricky. Are there affordable
testers for that?

What I described is a simple crossover cable. (Xmit pair to Rcv
pair and Rcv to Xmit.) Any cheap tester can report that. I have a
$5 one that does. But it can't detect split pairs that Cliff
described.

You must be describing something else but what?

I was thinking Cat5/6 ethernet cable, with three pairs. Same problem
of detecting switched wires that preserve DC continuity.



Oops, 4 pairs of course.
Click to expand...

Of course, but what kind of fault were you describing?
 
On Sat, 18 Apr 2020 22:46:59 -0400, "Tom Del Rosso"
<fizzbintuesday@that-google-mail-domain.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sat, 18 Apr 2020 18:49:57 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 18 Apr 2020 20:43:47 -0400, "Tom Del Rosso"
fizzbintuesday@that-google-mail-domain.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sat, 18 Apr 2020 08:03:59 -0400, "Tom Del Rosso"
fizzbintuesday@that-google-mail-domain.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Sat, 18 Apr 2020 15:55:00 +1000, Clifford Heath
no.spam@please.net> wrote:

It doesn't tell you when you have mixed-up pairs, like in an
Ethernet cable where you have a blue/orange pair and an
orange/blue pair.

I think modern Ethernet doesn't care.

What it doesn't care about is when a twisted pair goes from pins
1-2 to pins 3-6 at the other end, and 3-6 to 1-2.




Don't do that, and don't expect any simple tester to report that.
It would have to accurately measure 3-terminal mutual capacitances
or something. UTP would be especially tricky. Are there affordable
testers for that?

What I described is a simple crossover cable. (Xmit pair to Rcv
pair and Rcv to Xmit.) Any cheap tester can report that. I have a
$5 one that does. But it can't detect split pairs that Cliff
described.

You must be describing something else but what?

I was thinking Cat5/6 ethernet cable, with three pairs. Same problem
of detecting switched wires that preserve DC continuity.



Oops, 4 pairs of course.

Of course, but what kind of fault were you describing?
Click to expand...

I thought the issue was cable testing, and that mere pin-to-pin DC
continuity wasn't all that needs to be tested for cables with twisted
data pairs.




--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard
 
"Tom Del Rosso" <fizzbintuesday@that-google-mail-domain.com> writes:

Ricky C wrote:

Doesn't a terminated cable mean it has resistors built in? Wouldn't
that cause another pin to be excited?

Terminated witha a connector, as opposed to bare wire.
Click to expand...

Yes, that was my meaning.
And also, this should be reasonably automagic, not manual.

--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close..........................
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
 
On Fri, 17 Apr 2020 18:58:05 +0000, David Lesher wrote:

A friend asked me about cable testing. He has a need for a tester for
terminated cables.

I was speculating about something decoder based; Pin 12 on A end is
excited, and B looks for that AND looks at 1-11 and 13-40 for anything
that should't be there. Then light up pin 13, and iterate.

What's the Brane Trust's ideas on how to do this?`
Click to expand...

I have a RJ45/11 tester like that, super-cheap, like this one

https://www.wish.com/product/591fb4f5864e5c5ebd1ea9a7?
hide_login_modal=true
It has 8 LEDs on both end; energizes each one in turn on the base unit,
and shows what lights up on the other end of the cable. For the elderly
among us, there's a 'slow cycle' setting :)
 
David Lesher wrote:
"Tom Del Rosso" <fizzbintuesday@that-google-mail-domain.com> writes:

Ricky C wrote:

Doesn't a terminated cable mean it has resistors built in? Wouldn't
that cause another pin to be excited?

Terminated witha a connector, as opposed to bare wire.

Yes, that was my meaning.
And also, this should be reasonably automagic, not manual.
Click to expand...

20+ years ago here in SED, John Fields wrote about one of his patents in
this area. It could test 25 or more pairs of POTS lines. The
transmitter held all other lines low while it pulsed one line high.
Line 1 pulsed for 1ms, line 2 for 2ms, and so on. So it would work with
a receiver connected to as few as 2 wires, which would detect a positive
pulse and a negative pulse of different duration. It couldn't detect
split pairs of course, but was good for telco where lines go through
multiple wiring blocks and can get mixed up. His patent diagram was all
SSI and MSI logic with no CPU but I don't remember the year.
 
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