To measure the coupling between the IRIG-B signal and the 10 MHz clock in the timing distribution system, the IRIG-B cable has been disconnected from the GPS receiver output for about 100 seconds on Monday around 13:20 UTC, see the first figure.

During this period, the demodulation noise measured on the free running atomic clock, is reduced compared to a time with standard configuration, see the second figure (this is the phase noise at 10 MHz). The blue curve is getting closer to a smooth curve just driven by the low frequency noise of the atomic clock and of the DAQbox clock. However, there is still some exec of noise in the 10-20 Hz band, as well as some increased lines at 100 Hz (and harmonics). This might be due to coupling between the IRIG-B and 10 MHz signal inside the GPS receiver.

The third figure is showing the same kind of comparison for the 10 MHz signal monitored on a few suspended benches. The noise is a bit reduced at low frequency.

By the way, the ITF unlocked when we disconnected the IRIG-B cable. In theory, it should be possible to disconnect the IRIG-B for a short time without any serious impact. To be investigated sometime...