Two methods I didn't mention that this group might already be familiar with:
1) They still distribute time via telephone. Call 303-499-7111 to hear the WWV (colorado) broadcast or 808-335-4363 for WWVH (hawaii) 2) You can dial in with your dialup modem and get time codes. 300 baud up to 9600 baud. Beyond that they have a range of services, some of which are not on the website to distribute time and frequency to various other entities which need a NIST-traceable and/or highly accurate time system. Not sure how much detail you really want, but there are three main additional methods I'm aware of: 1) Two-way-satellite time and frequency transfer. Essentially they buy time on a commercial satellite to be able to do full duplex two way satellite communication. Because of the symmetric nature of the simultaneous two-way path they are able to cancel out any satellite delay. Lots more information at https://www.nist.gov/pml/time-and-frequency-division/time-distribution/two-way-satellite-time-and-frequency-transfer 2) Common view GPS. Essentially you measure the time you receive a certain part of the signal from a single GPS satellite at two different locations, and compare it to the time produced by the atomic clocks at that location. If the path to the GPS satellite is the same length at both sites because you picked a time that the GPS satellite was in that position, you can be pretty certain that any difference in time of arrival you measure between the sites is an inaccuracy of the atomic clocks at each site. This method doesn't depend on the accuracy of the GPS clocks on the satellites as you're just comparing time of arrival of the signal and not decoding GPS time. Of course, the devil is in the details here as there is often propagation delay differences, and you need very precise satellite orbital data to make this work. Oh, high accuracy GPS satellite orbit data is also available from NIST. See https://www.nist.gov/pml/time-and-frequency-division/time-services/common-view-gnss-time-transfer . Apparently they're also experimenting with comparing the phase of received GPS signals as well to get even more accuracy. 3) They also do experimental fiber-based time and frequency transfer. Doesn't take much imagination about how this works, other than to say that apparently you have to take into account the fact that light propogates down different fibers at different speeds (even in the same bundle). 4) If you need nist-traceable time at your site they also sell a service where they drop a rack of equipment in your site and manage it. You get a highly-accurate frequency and time standard that is NIST traceable with all of the reports to prove it, from NIST. Think all of the atomic clocks you need, along with NIST scientists handling the time transfer to that rack.
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