When I was in college, I worked as a broadcast engineer. This was for a 1kw AM/FM operation in a metro NY market, which at the time had Mutual Network News on the hour, for five minutes, followed by local news.
In July of that year (1960-something), we noticed that we began missing the network hookup, on the hour, by a few seconds. So I reset the clocks, and we came up OK the rest of the day. By the next afternoon, however, we were again missing by a few seconds. I reset again, all was well, and I wasn't scheduled to come in over the weekend.
By Monday we were missing the network by more than 15 seconds during morning drive time. I reset the clocks again, and all was well. But by Tuesday afternoon, we were again out of whack by a few seconds, and people were highly sensitized to what was obviously an engineering problem.
I had only adjusted the clock in the main control room through all of this. Checking the clock in production control, it had almost 45 seconds lag from master control... evidently having integrated the error.
These were synchronous motor driven clocks. I called the power company and asked if they had any idea why we might see clocks running slowly. There was some hesitation on the other end of the line, followed by: "oh, um ... maybe it has something to do with the peak demand compensation test."
Turns out the entire US power grid east of the Rockies was running at 57 Hz to 59 Hz instead of 60 Hz, during peak demand, and then increasing the frequency to 61 Hz or 62 Hz to catch up in the overnight hours, when demand was down. So the accumulated error would shift from day to day. The hope, evidently, was that the net shift would be so slight that nobody would notice, and would null out over time. But they obviously weren't trying to synchronize clocks.
I found a crystal time base driven clock to hang in master control, alongside the synchronous unit, and we had no problem syncing up with network. By the end of the following week, the experiment was evidently terminated; the clocks didn't reflect further drift, but no formal explanation ever came.
This entry was submitted by Jim Jarvis and edited by Rob Spiegel.
Jim Jarvis has BS & MBA degrees from Rutgers University. Leaving broadcasting after college, he has worked as a tech writer, apps engineer, product manager, and business unit manager in scientific instruments and T&M.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.