[Milsurplus] A New Concept: Virtual Spectrum

[w8au@sssnet.com]

At 11:47 PM 10/13/2003, William Donzelli wrote:
The concept of using the power grid for data transmission is older than
>most people think. Westinghouse was making power line data equipment back
>in the 1930s, for sending messages between the power stations.

Actually, the "data" exchanged by Carrier Current transmission over High 
Voltage
lines as early as 1926 (GE Carrier Set CC-3) was strictly AM voice.  No 
term such
as data was even applied to it.  It was for "area" substation dispatchers 
to communicate
with each other and exchange load reports and other necessary info.
Later on (mid thirties) the continuous transmission of "data," which was 
transcribed
onto chart recorders,  was called "metering."

Interestingly, the term "data" never entered the Electric Utility industry 
communications
vocabulary until the seventies/eighties when early SCADA modes came into 
play.  (Supervisory
Control And Data Acquisition)    Interestingly, these new "data" modes were 
mainly
transmitted over Microwave basebands, not Carrier Current.

Actually, the limited bandwidth of Power Line Carrier (traditional LF) is 
only 250 kHz.
(50 kHz - 300 kHz)  This led to it's demise as a major communications mode, 
with MW
and the new guy, "Fiberoptics," taking the major load.    Utilities use of 
PLC is very
minimal these days, with only "trip blocking" and "trip enabling" modes  used
between substations and power plants.

Sorry for the trivia....  just a few minor bits of info for those that find 
these things
interesting....   After all, PLC gear are really just 
transmitters/receivers on the LF
band.... non-radiating (?) cousins of our beloved LF Mil rigs....

How's that for a connection to your TAJ, Bill?   :-)

Perry    w8au    (First Energy Corp, ret.)