ethernet "stub"

I wouldn't do it. I don't have the specs, but I have a strong feeling that the stub would not be acceptable.

will

Definately. The open end produces 100% reflection of the signal, which will distort the signal in the 'main' line.

Meindert

one

other

will

But it may still work. Is this going to be shipped to a customer, or just for in-house 'playing'?

That requirement is really quite a sick one --- how did it come to that? This reeks strongly of some PHB having been involved.

What makes you so sure? You'll still have some kind of dangling stub cable, then --- be it just the pins of the RJ45 plug itself.

You've violated those the moment you mounted the second RJ45 plug anywhere else but at the end of the cable. You don't really believe they make all those prescriptions (like about how long the twisted pairs may be un-twisted when mounting the plug) just for the fun of it, do you?

It will certainly cause reflections, but whether that causes problems or not is a question of the parameters involved --- particularly the length of the dangling stub. As soon as its length comes anywhere near a bit-time's worth of cable length, you're in serious trouble. For 100baseT, that's roughly a meter.

In other words: it's high time to very seriously re-evaluate that requirement.

--
Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

I should have explained this better. The application consists of a board that does a few things (motor control) and plug into a custom backplane. The backplane connector has an ethernet (100BT) connection and is connected to a hub that is not accessable from outside. In certain configurations, the board is not present but a "simulator" runs on a PC which needs to be connected to the same ethernet pairs. The "stub" in question is approximately 1 inch of copper traces.

|

I don't think it makes any sense to do that job by means of an additional RJ45 jack. A dummy board to go into that empty slot and connect it to another RJ45 jack would be a more common and less worrysome solution.

[Note: your drawing was completely garbled because you forgot to use a fixed-width font to design it... ;-(]

--
Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

A proper new messages is 7 bit ascii, no font info. So the font setting of the poster is not important. The font setting of _your_ newsreader should be set to fixed width if you want to see the drawing right.

Meindert

Mine is set to fixed width. Still the drawing does not right to me.

Regards.

Elder.

I meant "does not look right".

of

should be

O shoot, now I see it. I started type before thinking......:-(

Meindert

You might check the ham forum on usenet. Considering the wave length of

100 mhz is about 10 ft., a 1 inch stub would appear of minimal concern.

Hul

bta3 wrote: : :>

:> But it may still work. :> Is this going to be shipped to a customer, or just for in-house 'playing'? :>

:>

: I should have explained this better. The application consists of a board : that does a few things (motor control) and plug into a custom backplane. The : backplane connector has an ethernet (100BT) connection and is connected to : a hub that is not accessable from outside. In certain configurations, the : board is not present but a "simulator" runs on a PC which needs to be : connected to the same ethernet pairs. The "stub" in question is : approximately 1 inch of copper traces. : : |