[Milsurplus] A New Concept: Virtual Spectrum

[Morrow, Michael A.]

-----Original Message-----
> From: William Donzelli
> 
>> 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.
> 
> Sounds very neat. The information I have is for a Westinghouse
> system, and I am pretty sure it is somehow based on tones.

At the generating station and switchyard where I work, we use power line
carrier signals on the 500 kV and 161 kV lines coming into the switchyard.
They operate anywhere from about 150 kHz up through the upper AM broadcast
band.  Each power line carries typically two protective relay coordinating
carrier signals, one from each end of the line (sent out momentarily from
one switchyard to the other end of the power line to either delay or permit
remote line breaker tripping), and four continuously present unmodulated
signals, two from each end of the line (when the appropriate modulation is
applied, it causes the breaker at the far end of a power line to "remote"
trip).

It was concern about potential interference to these types of power line
carrier signals that caused some industry groups to protest a ham 136 kHz
allocation.

These signals are carried on the B-phase of the three-phase power lines,
with tuning units to couple the receivers and transmitters to the line and a
huge RF choke called a wave-trap at each end of the line to prevent
grounding out the PLC signals through the transformers connected at the
switchyards.

Mike / KK5F