I was really glad they covered carrier current, this obscure and cool form of radio. I'll agree with KDX Radio that they were vague in the technical area and how this type of broadcasting does its job, but I don't think they have an electronics person on staff and seem to be more oriented toward programming issues. I thought the info they shared was pretty solid though, above the average intelligence of most radio hosts.. :)
Part of it is the obscurity, it's hard to find good info on carrier current broadcasting that doesn't go on for 20 pages about the art, like the old LPB manuals and guides do.
I wonder how electrical wiring became the dominant to use, compared to gas pipes, phone lines or other wires that could be installed at a school? My guess is that since tube-type radios were plugged into the wall, they'd receive signals from the electrical lines better, which is talked about in some of the guides.
I like how hams were doing it in WWII, using it on longwave frequencies with home built transmitters and receivers. The Radio Amateur's Handbook from 1944 has a whole section dealing with carrier current for two way communications, coupling the transmitter into the AC lines at one end and out to a receiver at the other end, using the lines as a direct cable.
I've pulled out the section on carrier current and saved it as a new pdf at the following link. It comes from the 1944 Handbook, as published on line several years ago.
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boomerthedog.com]
Boomer