Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!julius.cs.uiuc.edu!rpi!masscomp!peora!tarpit!tous!alfred!fang!att!westmark!dave
From: dave@westmark.WESTMARK.COM (Dave Levenson)
Newsgroups: comp.dcom.modems
Subject: Re: Why do they insist on power cubes???
Message-ID: <2349@westmark.WESTMARK.COM>
Date: 5 Jan 91 16:58:55 GMT
References: <191@raysnec.UUCP>
Distribution: usa
Organization: Westmark, Inc., Warren, NJ, USA
Lines: 34

In article <191@raysnec.UUCP>, shwake@raysnec.UUCP (Ray Shwake) writes:
> 
> 	What began as an annoyance has become a logistic mess. Some years
> ago, manufacturers of external modems like Hayes moved their power supplies
> to external power cubes which fit directly into the power line. A small
> power lead then fed the small, stylish modem. While some (like Prometheus)
> kept to the internal power supply, most others followed the move to power
> cubes.


The first modem to have its power transformer mounted externally was
the AT&T DataPhone 1200, also called the model 212 modem.  This was
the first full-duplex dial-up 1200 bps modem, and was also one of
the first to be packaged in the new smaller size.

Putting the transformer out side accomplished two purposes:

It reduced the internal temperature of the modem enclosure.  This is
because the transformer tends to radiate more heat than most of the
rest of the circuit.

It allows a group of modems to be plugged into a rack, rather than
being mounted in individual enclosures.  A common power supply for
the whole rack is less expensive than a bunch of individual
transformers.  Also, it keeps the high voltage contained close to
the outlet or other power source.  With no line voltage present on
the modem circuit pack, less human-sheilding is required to meed
safety requirements.  The rack-mount strategy is expensive if you
have 117 volts running around inside the rack!
-- 
Dave Levenson			Internet: dave@westmark.com
Westmark, Inc.			UUCP: {uunet | rutgers | att}!westmark!dave
Warren, NJ, USA			AT&T Mail: !westmark!dave
[The Man in the Mooney]		Voice: 908 647 0900  Fax: 908 647 6857