How to Adjust the Sigma Tau Maser Rate
- Plot the GPS offset versus time for the past few weeks.
- Using, for example, "llogsum" or "rfclock" (ref: ~fghigo/bin/ )
- "GPS offset" is Site1Hz vs GPS (or TAC) from the GBT Timing center.
- The sense of Site1Hz vs GPS is positive if the Site1Hz rising edge precedes that from the GPS.
- Fit a line to the GPS vs time data, get slope in ns/day.
- Convert to seconds/second, R = dT/T = slope(ns/day) / (24*3600*1e9)
- Divide by 4.659e-17 to get maser synthesizer counts: R* = R/4.659e-17
- or in one step: counts = 248 * slope in ns/day
- Open the front panel of the Sigma Tau Maser and note the present setting of the synthesizer.
- Subtract R* and set this new value in the switches.
- If R* is positive, decrease the value, otherwise increase, to cancel the trend.
- Write up the change in the log file : ~fghigo/public_html/timer/STmaser.log
R = 3 / 8.64e13 = 3.47 e-14
R* = R/4.659e-17 = 745 counts
Suppose the synthesizer reads 86,930,990,600
R* is positive, so to counter the upward trend, lower the synthesizer by 745 counts.
new synthesizer value should be: 86,930,989,855
- Lets say the Site1Hz vs GPS rate is 3 nanosec/day over the last 2 months.