Was doing some SDR scanning tonight and came across a bunch of strong signals in the 72Mhz band. The data signal is a MFSK-like signal with a bandwidth around 300hz wide, roughly 35 baud.
So apparently these are quite popular. Companies have a GPS-based receiver on the roof with a 72Mhz RF transmitter which can be picked up by digital clocks around the campus and/or other time-sensitive equipment.
Here's a company that sells the gear:
https://www.primexinc.com/clocks/xr-series/
Looks like the signals from around here were coming from Children's Hospital --> http://wireless2.fcc.gov/UlsApp/UlsSear ... ey=3118403
The RF power output can vary from 1W, 5W or 30W -- at least the model from the above company.
Oddly, the Children's transmitters stopped at 1AM local time. EDIT: They came back on at 1:40AM. Possibly only on for 20 min or so?
Did a wider FCC search and quite a few companies are using these GPS-clocks.
If anyone knows a decoder tool that information would be much appreciated.
Here's a screenshot of the signal:
