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From: rjn@hpfcmp.UUCP
Newsgroups: comp.dcom.modems
Subject: Re: Reliability of Modular Jacks
Message-ID: <980001@hpfcmp.HP.COM>
Date: Sun, 22-Feb-87 13:05:30 EST
Article-I.D.: hpfcmp.980001
Posted: Sun Feb 22 13:05:30 1987
Date-Received: Thu, 26-Feb-87 20:39:41 EST
References: <267@aucs.UUCP>
Organization: Hewlett-Packard, Ft. Collins CO
Lines: 35

re:  Use of RJ-series modular plugs/jacks in computer applications

I strongly discourage the use of RJ connectors for anything other than telco
applications, due to the damage potential of telco ring voltage.

An alternative is the AMP SDL (Shielded Data Link) family of connectors.
These are based on the same wiping-wire design as the RJ, but:

* Are mechanically incompatible with RJ.  You can't insert an RJ into an SDL
  socket, and vice versa.  The SDLs are thinner from top to bottom and are
  wider due to having the latches (2) on the sides.

* The SDLs are shielded, which reduces EMI emissions and reduces EMI and
  static discharge susceptibility.  If you are building a product for sale,
  you are extremely unlikely to pass FCC Class A / VDE A (much less B) if
  you send data any faster than audio frequencies thru unshielded RJ cable.

* The housing of the SDL is metal, and is longer than RJ, providing better
  strain relief.

* SDLs are available with mechanical keying, in case your cabling is not
  symetrical, or in case your devices (like ours) have an "upstream" and
  "downstream" socket.  Be aware, tho, that it is possible to force a
  miss-keyed SDL plug.

HP uses SDLs for our HP-HIL (Human Interface Link) daisy-chain interface to
keyboards, mice, tablets, knobs, barcode readers, touchscreens and other
desktop critters.  We're reasonably happy with SDL.  Early HP150 PCs and our
current Series 300 4-port MUX are RJ-equiped, and I have heard stories of
folks blowing them up by plugging them into phone lines.   This can't
happen (and hasn't) with SDL.

Regards,                                              Hewlett-Packard
Bob Niland                                            3404 East Harmony Road
[ihnp4|hplabs]!hpfcla!rjn                             Fort Collins CO  80525