🚀 go-pugleaf

	To continue the discussion about communicating on the power
line: digital and analog coms have been around for quite a while.
Powerline coupled intercoms have been around longer (I recall having a
baby monitor in the house nearly thirty years ago that worked quite
well over the power lines.)

	The big problem (as mentioned earlier) is to get the signal
around the transformers. This can be difficult in buildings and out on
the street where its not common practice for your average
engineer/technician/comnerd to be allowed to add bypass caps. You can
also get seriously killed messing around with power transformers....
Please be careful. If you spec bypass caps, be sure to check the
heating induced by ripple and to get the voltage rating high enough.
If they fail shorted, you get a big bang and then the lights go out ;-)

	We have done a multi-drop telemetry system on a 3 phase 440VAC
power line for a vertical pump array (hangs from a ship at sea) by
using power line modems that we bought from Carrier Current
Technologies, 6505 Pharr Mill Rd. Harrisburg, NC 28075, voice
704-455-5505.) The protocol was run by a master (pc clone running
MS-DOS) processor at the surface that addressed each remote in turn.
We built and coded the remote processors boards ourselves. Error rates
(for 1200 baud) were neglidgible after some early problems with timing.

	In my "power line modems" file there is a reprint from
Electronic Design, Oct 2, 1986 written by Dan I. Hariton and Paul F.
Patterson of Signetics which discusses the design parameters for a
carrier current modem based on the Signetics NE5050 power line modem.

	I also have an article "Build a pair of line-carrier modems"
by Keith Nichols which appeared in the July 1988 issue of Radio
Electronics. This design is based on an Exar XR2207 FSK modulator amd
the XR2211 FSK demodulator.

	National Semiconductor makes an LM1893/LM2893 carrier-current
transciever. My data sheet is from October 1986, but it is also
found in the current National Linear data book, volume three with a long
discussion about design and application. 

	Cyplex makes a commercial system which is targeted at factory
floor and industrial installations. I didn't explore this route
because the physical boards were much too big for our application. 
Cyplex 4 Kidder Rd, Chelmsford, MA 01824, voice: 617-256-1918.


Caution: some of these address/phone numbers may now be out of date.

Have fun and be careful,
-Dal

-- 
Dale Chayes
Senior Staff Associate
Lamont-Doherty Geological Observatory of Columbia University
Route 9W, Palisades, N.Y.  10964