I recently acquired a couple vintage simplex clocks that used to be in a high school. They were part of a clock system where a master clock controlled the whole operation of slave clocks.
There were basically three systems: impulse, wired, and electronic systems. The clocks I have are electronic systems, where there is only a 110V AC plug. The clocks have a continuous motor and to keep them at the correct time (in case power wasn't a truly clean 60Hz) was to send signals over the electrical lines. On the limited information I have, I believe this signal was 3510 Hz. Two different durations of signals were sent. 1) An 8-second pulse at 57 minutes, 54 seconds on the hour for hourly corrections and 2) a 14-second pulse at 5:57:54 am/pm for 12-hour corrections. These pulses energized a solenoid that caused certain gears to catch and rotate the hands of the clock to the correct positions.
I can easily code up a program that sends audio signals at the specified frequency for the needed durations at the correct time but don't know how to send those over my home electrical lines (I only had a circuits class in college.) Any ideas on how to implement a home-brew inexpensive solution to send these signals?
EDIT: Here are some photos of the clocks in question.