The site timing center contains the hydrogen maser frequency standards used throughout the site, as well as the IRIG source and 1PPS sources.
The site timing center is also the source of all the phase-locked LO reference signals used by the telescope. A 100 MHz signal generated by the maser is multiplied by 5, and combined with the 10 MHz signal. It is then split into 4 outputs, each of which may be transmitted to a different location. The combined signal is then put on an optical fiber and transmitted to a user station. The Green Bank site has user stations at the 140 ft telescope, the GBT equipment room (at the Jansky Lab), and on the GBT. A fourth station will be installed in the Jansky lab for other telescope usage. At the user stations, the 500 and 10 MHz signals are recovered, resynchronized, and made available to the users. The 1PPS is also resynchronized to the 500 MHz and the 10 MHz. A Round Trip Phase Measurement Module (RTPM) [6, 7] as described in Sect. 5.4 is provided to measure the changes in phase of the signal for each user station.