I like the idea of on-frequency boosters for AM broadcast stations, and cool that Ernie from Panaxis showed how it could be done, even back then. I think the idea was tried as far back as the 1920s, after transmitters switched to quartz crystals that could be tuned tightly on frequency.
They tried different things, like oscillators in ovens at exact temperatures for stability, and having an operator listening between two transmitters and remotely tuning them to zero beat when they drifted.
Today synchronization could be done automatically, GPS could be an obvious answer to do it cheaply, with other frequency standards like digital TV, which I think is being worked on now, maybe WWVB timecodes.
For independent sync, you could have a master oscillator and then slave units locked to it somehow, could it use pilot tones, or receive and sync with the main signal at to stay in phase, maybe with a master receiver between the signals?
Another issue on a tighter system with a lot of overlap in the signals is keeping the audio time-aligned too. Without that you'd get echo and hear audio phase differences.
These days I think AM sync is a good idea, getting a better signal close to dense groups of listeners in outlying small towns, with low power transmitters and small antennas within your coverage area.
Here's a question though, if you were a 1000 watt station, and you put a few, let's say 100 watt boosters around town, would you need to turn your main transmitter power down to 800 watts to maintain your total ERP going by the rules?
Silicon Carbide FETs are dropping in price after a few years of being out. They're still considered industrial devices, but I saw some at $10 on Mouzer for lower spec transistors. When compared to tubes these days, not bad.. ;)
Boomer
