So, I had time today to do some testing. I have a TH 5 that I have been experimenting with. Audio is fair, not great, but I will iron that out after I get through playing with coverage.
I own a facility in my small town, it is old, the electrical is mixed, some is very modern, but the original feed point is 50's, and in good shape. I am in the process of upgrading the service in another part of the building, and will eventually back haul into the old part and update it.
The brief history above is relevent only because of what I did during my experiment. My master disconnect is separate from the breaker box...thats how it was specified on the original blueprints (I have them). I originally tied the output wire of the TH to the neutral (after testing for stray voltage with voltmeter etc.. BE SAFE!). I got no match with the TH built in tuner, which is what I expected. The TH is not capable of matching anything other than the app 10 ft wire or an antenna of similar length.
I then, attached an insulated wire from the neutral (my building is conduited) and wound the TH wire antenna around it to produce a crude coupling. I got zilch, and worse coverage than the wire antenna provides stretched out, but the built in tuner did match.
On further inspection, I noticed that the neutral had been bonded to the conduit (which runs into the slab through the building etc) to use as a supplemental ground (against code..yep!), and was obviously an added "feature". I removed the bonding wire, tested for stray voltage again (BE SAFE!), and reattached directly to the TH.. no match again, no surprise.
I then, wound the wire antenna around my insulated wire, TH tuner match obtained, and I noticed my GE radio about 10ft away was being overpowered with signal...progress???
A radio in another part of the building was clear and without AC line noise growl, which is prevalent in my area.... progress...YES!
A quick test drive shows that I had excellent coverage for 2 blocks south and 1 block north. I had coverage 1 block east and approx 3 blocks west. In all cases, the signal was strong then abruptly stopped. Line noise growl was also present, it always is there on AM though.
Was the test succesful? Yes in some ways. First, coupling without a "hard connection" to the neutral is clearly possible. Is it feasable to continue with CC at this point for me? I am leaning towards "no." But, I will continue with a few more tests. Obviously, I don't have the equipment yet to do a hard connection to powered side. I am wary of even a "coupled" connection to the powered sides like I did on the neutral for safety reasons, but I may do some tests to see if a short term coupled connection would be safe.
100 milliwatts from a TH is enough to start a CC feed is what I learned. I am sure that more wattage would be stronger, but I am not sure how much farther it would reach on the neutral in my case.
Sorry for the long post. But, I thought it was worthy of passing on what I "think" I found out so far.
BTW, if you attempt this, be sure you know what you are doing. I have several years of experience in a variety of things, including things electrical. I would rather not read about you in the news, on here, or as a subject of a "darwin award."
Craig
In support of what craigf has discovered... while my CC neutral injection was operating (the transmitter is out of order for the time bieng) I discovered that it worked quite well when I turned the power down as far below 1 Watt as it would go...
That's some thorough testing, and it's good that you found the neutral was bonded at the conduit so you could fix that. It seems when you wrapped the Talkinghouse antenna around the unbonded neutral wire, it would make a capacitive connection since the loop is right angles to the wire it's wrapped around.
It's good that you were ablr to tune up, my older TH wasn't able to do it with the antenna wrapped that way around a single phase power line, it tried and errored out. I could have unwrapped some wire and tried again, but didn't go that far.
I too have noticed abrupt drops in the carrier current signals, usually at intersections at some distance, and lots of times it will get stronger before the drop, like it's at an end point on the last loop of neutral to ground, then it becomes another section of the grid, fed from a different branch of the power system, my impression of what's happening from my little knowledge of how power grids are set up.
I think sections are smaller in the city, which could lead to smaller coverage areas there, but a higher density of people, where in rural places the lines feed larger areas, and with less loading on the lines and lower noise you'd get more distance coverage.