After the new PID parameters were tuned (CTN:2428), I waited for some time and the beatnote was stably locked to its setpoint of 27.34 MHz for over 2 weeks now. It is a good time to assess the beatnote frequency stabilization. Here I took data of 10 days and plotted it in three different timescales. The standard deviation plotter in light blue is calculated by standard deviation over 10 s of averaging of data. Green background means everything was locked at that time. Other than green would mean that either something was unlocked or there is a gap in the channel data (this case).

Conclusions:

• Over 10 days, the beatnote hardly left +/- 2 kHz zone from the setpoint. Even with one standard deviation far away, the beatnote does note leave +/- 2.5 kHz zone. We are using Moku at 2.5 KHz bandwidth right now.
• Over a day, here it was Sep 28th (Saturday), the beatnote is within +/- 2kHz even up to one standard deviation point. 
• Over 1 hour which was between 1 am to 2 am on Sep 28th, the beatnote was similarly calm.
• In the last plot, I have plotted drift over 60s in beatnote frequency which is our measurement duration. This drift doesn't even cross 1.5 kHz mark.

But

How good is good? We were so bad, I never did this calculation. Are we hitting boundaries of how good the thermal controls can anyway do? Is the remaining noise in beatnote spectrums just scatter noise or there is still room for improvement in beatnote stabilization. Food for thought.

Code and Data