Carl, you're absolutely correct - 15.221 has no limitation on power - as with the FM rule, it is solely a field strength limitation. And the calculation favors the low end of the band. It works out to about 300 ft / 100 m from the power line. Kicker: With Neutral Loading, you can bypass the transformer's "natural" filtering, and get some significant ranges, depending on just how long that neutral run is between grounds. As an aside - when I was running some tests, I discovered that such a system can also gain some NVIS coverage - Near-Vertical-Incidence Skip. The footprint is rather small by comparison, but it's possible. I received the test signal at about 3 miles from the station - well beyond the direct/groundwave, which had faded out about where expected. I double-checked against possible conducted signal - and where I was getting the signal had no direct connection - different substation, even - to the primary lines.
Carl ...
On your very own site you have photos and a LPH interview with "RF Burns" CC setup which IIRC uses a Radio Systems TR-6000 TX and is in operation even as we speak. So, what's wrong with what he's doing?
Don't forget there are necessary peripherals (e.g., the coupler) for the LPB CC TX, even if you can find a working one for the price. Plus you need to have a maintenance schedule for keeping everything properly tuned and attenuated as necessary. It's a cool way to do Part 15 broadcasting, but it's definitely work.
Neutral injection does indeed bypass most transformer issues. I have no idea what the local power company would say about injecting a signal onto their system, or even if they would care. I know for a fact no one has a CC signal in my small town, or anywhere in the county ... 4 ferry-served islands and many more that get power from OPALCO, which BTW, is a co-op. If you pay a power bill to them, you are automatically a voting member. It also has great management, we pay one of the lowest rates in the state.
Thank you Ken Norris for bringing the CC subject back to the front. Ya, this thread started back before interviewing RFBurns, and his setup is now a major inspiration, and he'll be joining for a Part Two Show on CC sometime soon, I hope.
The reason I wanted that older LPH transmitter was because it has a variable power setting, and I think the now available transmitters are set at a particular output and would need to be attenuated accordingly, which seems like a waste of energy.
Also, I hope we find a leaky-cable operator who is ready to come on air and discuss that very curious way of doing part 15.
There's a circuit here on this website for building a 5-watt variable power transmitter, and I might try that as a starter tool.
First, my apologies, "RF Burns" is running a LPB unit.
Very strangely, the Radio Systems TR-6000 is shown both as a variable output transmitter up to 30 watts, and also (on the same site) as 10 watts. Confusing ... I'm going to have to email them and get the straight skinny. iAM, same people that sell Talking House AM transmitters, sells them, and also the companion CP-15 Coupler, but with no prices available online, either form Radio Systems or iAM.
Also, Radio Systems shows BSW as a dealer, but I couldn't find it in a catalog either online or off.
I believe the TR-6000 output can be adjusted, and is touted at 80% efficiency. The CP-15 Coupler is rated at 20w max input, so you'd have to attenuate at least to 20w if you want to use that coupler.
Still, that should be enough to get you where you want to go.
Leaky cable seems very similar to CC. Drive-in movie theatres were using these things all over the place (remember drive-in movies?).
For FM there are no further caveats I know of that would preclude using leaky cable as the antenna ... IOW, you still can't have more than 250 uV @ 3m from the emission source. But a leaky cable around a large parking lot could be fed from something like a Decade 850 with an RF power amp, carefully adjusted to meet the regs, with all the measurements recorded and filed. Some good coverage, though.
Pro gear that can do that aren't toys, either. I'd get some really good engineering advice, come up with a viable business plan, and start looking for used gear ... but it would surely be a rare find! New stuff is spendy ...