Modulator plus amp plus antenna equals illegal fun
When I was much younger, I used some technology in a way it probably was not intended to be used. At the time, it all seemed simple enough, and logical, too. What works one way must work the other. This is what happened when I actually tried it.
At some point, my family had purchased a full-size VHS camera. It was the thing to do for a while there. This particular camera came with a little AC adapter box which had video and audio inputs and outputs, but it also had a pair of coax connectors on the back. You could hook it up to your antenna, or cable, or whatever, and then hook the TV to that. In that sense, the camera could also act like a VCR, in that it would seize the feed and inject its own content on channel 3 or 4 when you turned it on.
Inside our house, we had abandoned cable some years before, and installed our own little extension line to the far end of the house. Watching this happen taught me a bit about TV signals, and how they tend to degrade, and all of this. For one reason or another, we wound up installing an in-line amplifier from Radio Shack right where the antenna feed came in, before it went to any splitters. This made things look pretty good. That, plus a fair amount of yelling back and forth to aim our roof-mounted antenna gave us decent pictures essentially for free.
I had already discovered that I could connect our camera's coaxial output to the splitter, replacing our antenna feed, so then you could watch it in our distant room. It worked okay, but it got better when I hooked the box up in front of the amp, just like the antenna was.
Well, anyone who's ever played with this kind of stuff probably knows what happened next. There I was, experimenting, and I had this awesome signal booster going into our inside cabling, and our antenna coax was just hanging there. I figured, well, could it work? What if I put that antenna on the output side of our booster? What happened then?
I propped that camera against some stuff and pointed it in the general direction of our front door. Then I hooked it up to the antenna, turned that gain all the way up, and looked around. Nothing was catching on fire, or sizzling, or anything. It was a whole lot of nothing. Then I remembered my little portable black and white TV, and got it out. There it was: our front door, with one of our cats hanging out in front! Wow!
We called a neighbor who we knew had at least one TV with an antenna instead of cable. We asked her to put on channel 4, even though there was no channel 4 in our area. Well, today, that was false. That day, there was, assuming you lived right in the path of our antenna. She came back to the phone: "I can see your kitty!" ... so, yeah, it worked. I didn't leave it on, since I had proven my point, and there wasn't much more to do with it. Also, I knew at some level, it was wrong.
Obviously, this probably violated a half-dozen FCC regulations and created interference and all of that other stuff. I'll just say that it happened a very long time ago, and I was still in middle school, so forget about coming after me for it now.
There is one sad note about this. The way things are going, this will quickly become impossible. I imagine TV sets will stop tuning NTSC off the air soon, if they haven't already, because there are fewer and fewer sources of it as time goes by. There's certainly nobody out there with a plain old NTSC set with a bare antenna feed, for sure, since it's been dark for a couple of years now.
I don't suppose many kids will get to have their own "Cat TV channel 4" in the future. They will have to settle for YouTube or whatever else we use to transmit video at that point.