stefan.ballmer@LIGO.ORG - posted 02:08, Monday 17 August 2015 - last comment - 08:13, Monday 17 August 2015(20582)
45MHz oscillator phase noise measurement
Evan, Stefan, Evan will make a more detailed log entry with actual measurements, but here are the highlights: - We beat the 45Mhz signal from the installed and the spare harmonic generators. - the first odd thing was that straight out of the harmonic generators, the 45Mhz signals were out of phase by about 170deg, even though the 9MHz inputs were nicely in phase... - We phased the two signals to be exactly in phase an stuck them into a mixer: 0.415V - We phased the. To be exactly 90deg apart: no DC signal, and ~ 220nV/rtHz of flat broadband noise. - this gives 5.3e-7 rad/rtHz between the two signals. - Assuming equal and non-coherent contributions, the phase noise of one box is thus: 3.75e-7 rad/rtHz - If we assume that the oscillator phase noise has the same coupling as the oscillator amplitude noise (9e-2mA/RIN), we would expect 3.4e-8mA/rtHz. Thats's pretty close to what we see on ODC_DCPD_SUM.
Data attached: two amplitude noise measurements, two phase noise measurements. One set taken sending equal drive levels into the mixer, and another set taken with the rf attenuated by 5 dB.