UTC Time Check
Before the days of GPS the frequencies were crawling with time hack stations. Most of those, alas, are gone. The frequencies 5000, 10000, 150000, and 25000 got you something almost everywhere in the world. These days those frequencies are pretty much just in the United States, but you might get lucky.
The National Institute of Standards and Technology (NIST) broadcasts on the following frequencies from the locations noted:
|2.5||40°40'52.2" N||105°02'31.3" W|
|5||40°40'42.1" N||105°02'24.9" W|
|10||40°40'47.8" N||105°02'25.1" W|
|15||40°40'45.0" N||105°02'24.5" W|
|20||40°40'53.1" N||105°02'28.5" W|
Through the Internet
Most of the dedicated sites for UTC have gone away because you can simply type "UTC Time Check" into your favorite search engine.
Through the GPS
Photo: G450 MCDU Nav Ident page, from Eddie's aircraft.
UTC Time Check (http://utctime.org/)