RE: [SI-LIST] : Ethernet RJ-45 connectors

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From: Larry Miller (ldmiller@nortelnetworks.com)
Date: Wed Jul 05 2000 - 07:32:22 PDT


Some answers from our neighborhood:

1- how critical is the RJ-45 connector in 100Mbit Ethernet data
transmission? Is it
    required to use category 5 connectors or is this not important?

The connectors are the weak part of the link, especially with respect to
crosstalk (NEXT). They are the limiting factor, for example, in the IEEE
802.3af committee effort to provide a mid-span power insertion point for
Voice Over IP (VoIP) data telephone systems to be retrofitted into legacy
equipment installations.

If you do not use connectors rated as "Category 5" you will probably not
meet the Standard bit error rate at some link distances (not necessarily the
maximum). Also, you probably will have problems with 1000BASE-T (Gigabit
Copper).

Short answer: Use Category 5-rated connectors.

-2- Am I correct to associate the larger sized RJ-45 with category 5? What
is different
    in their mechanical design? Spacing between the connector pins to
control connector
    crosstalk and signal integrity?

Not necessarily. The main distinction for Category 5 is better control of
impedance going through the mated connectors and lower crosstalk. This may
be achieved by internal metal bits, etc. Spacing of the pins after they
leave the connection area is another difference. The overall size of the
connector does not necessarily show whether it is Category 5.

-3- Is there a difference in EMC performance of both sizes? Does a category
5 connector
    radiates less than a non-category 5, so to speak!

It might be somewhat better, but crosstalk and impdeance matching are the
real issues.

-4- one category 5 RJ-45 connector drawing carried the following statement:
"jack
    cavitiy conforms to FCC rules and regulations, part 68 subpart F". I
assume that
    this is related to safety and isolation voltages?

FCC regulations are about EMC, not safety. Practically any connector will
meet regulations, but shielded ones (with a metal shell that can be
grounded) are a necessity.

I hope this helps,

Larry Miller

> -----Original Message-----
> From: jvercamm@roam.agfa.be [SMTP:jvercamm@roam.agfa.be]
> Sent: Wednesday, July 05, 2000 12:49 AM
> To: si-list@silab.eng.sun.com
> Subject: [SI-LIST] : Ethernet RJ-45 connectors
>
> hello,
>
> I have signal integrity - EMC questions concerning Ethernet RJ-45
> connectors.
> I have done some browsing on dimensions of these RJ-45 connectors and I
> have
> found that they seem to come in two sizes: a smaller one with a body
> length
> of 19.2mm and height of 12.2mm and a larger one which is about 21.3mm of
> length
> and 13.6mm high. The width of 16mm of the connectors is about the same for
> both
> sizes.
>
> It seems that the larger type is a category 5, the smaller one does not
> seem
> to comply with cat. 5 as one can gauge from the AMP web site.
>
> Currently we use the smaller type, which is likely non category 5. Our
> hardware is
> designed for 100Mbit twisted pair. I have looked at two other Ethernet
> 100Mbit designs
> (in new PC and in a Sun workstation) and I have found the smaller sizes.
>
> These are my questions:
>
> -1- how critical is the RJ-45 connector in 100Mbit Ethernet data
> transmission? Is it
> required to use category 5 connectors or is this not important?
> -2- Am I correct to associate the larger sized RJ-45 with category 5? What
> is different
> in their mechanical design? Spacing between the connector pins to
> control connector
> crosstalk and signal integrity?
> -3- Is there a difference in EMC performance of both sizes? Does a
> category 5 connector
> radiates less than a non-category 5, so to speak!
> -4- one category 5 RJ-45 connector drawing carried the following
> statement: "jack
> cavitiy conforms to FCC rules and regulations, part 68 subpart F". I
> assume that
> this is related to safety and isolation voltages?
>
>
> Thank you for your time.
>
> Regards,
>
> Jan vercammen
> EMC/PCB engineering Agfa-Gevaert NV, Belgium
>
>
>
>
>
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