Alejandro Acosta <alejandroacostaalamo@gmail.com>:
"The built in high sensitivity GPS receiver is able to lock multiple satellites from within multiple buildings or from a window location*, eliminating the requirement that an outdoor antenna be installed*."
Even relatively low-end GPS hardware can do this now. https://www.ntpsec.org/white-papers/stratum-1-microserver-howto/ That's my recipe for a GPS-based Stratum 1 server built from a RasPi and any one of several generally-available GPS daughterboards. Cost less than $100. A window location works just fine. I have six of these on the windowsill above my desk - they're my test fleet for NTPsec. The trees near the outside of that window aren't a problem, and while it isn't *guaraneed* that you have a 4-satellite lock at any ven time periods of no tracking tend to be short. -- <a href="http://www.catb.org/~esr/">Eric S. Raymond</a>