NOTES ON ADJUSTMENT OF SAO MASER AT THE 140-FT =============================================== (F.Ghigo, 8 Feb, 1994; NRAO, Green Bank, WV) ( revised Aug 1996; April 1998) 1. Coarse adjustment of the 1420 MHz frequency is done with the synthesizer at the bottom front. Remove the lower front panel to get access. The low order digit of the synthsizer is in units of 0.001 Hz. Decreasing the synthesizer number INCREASES the frequency. (I.e., if you want the clock to run faster, decrease the synthsizer. Recent changes: before Jan 1993: 0405751.691 HZ 29 Jan 1993: 0405751.692 8 Feb 1994: 0405751.693 2 Aug 1994: same 5 Aug 1996: same 23 Oct 1996: 0405751.694 15 Apr 1998: 0405751.696 2. Fine adjustment is done with the dials behind the top front panel on the right. The top (frontmost) of the three stacked dials has 100 divisions for a full rotation. Each division is 1.6E-5 Hz change in the (~1420 MHz) maser frequency. Increasing the number on the dial INCREASES the frequency. Recent changes: Top dial reading ---------------- before July 1992: 49 23 July 1992: 45 29 Jan 1993: 62 8 Feb 1994: 51 2 Aug 1994: 94 5 Aug 1996: 99 23 Oct 1996: 37 3. Adjustment of the delay in the 1 Hz timing pulse is done with the thumbwheel switches behind the second panel down from the top in the front. The low order digit is microseconds of delay. 4. To adjust the rate, it is easiest to compare the 5 Mhz output of the SAO maser with that from another time standard, such as another maser, and adjust the rate to match the other maser. This can be done using the NRAO "Frequency Standards Comparator" (or phase meter). Connect the two 5 MHz signals to be compared to the A and B inputs, and set the attenuators so that both meters read 100. Set the toggle switches on "100 ps" and "phase", set the time constant on 10. EXAMPLE: 5. As an example, here is what was done on 8 Feb, 1994. The scale on the right-hand meter (of the phase meter) is set to 100 ps full scale (set scale with knob 2nd from the right). Center the needle on the right hand meter using the coarse adjust knob and the 10-turn pot. With the 100ps setting, 0-100 on the meter is 0 to 100 ps. Suppose that the meter drifts 100ps in 2 minutes. Then the drift rate is: (100 ps)/(120.E+12 ps) = 8.33E-13 To get the frequency error at 1420MHz, multiply by 1420E+6: 8.33E-13 X 1.42E+9 Hz = 1.183E-3 Hz. If the SAO maser is running faster than the reference, then we must decrease its frequency by 0.001183 Hz. To do this, first increase the synthesizer by 1. This will change the frequency by .001 Hz. The remaining error is: 1.183E-3 - 1.0E-3 = 0.183E-3 Hz Divide by 1.6E-5 to get the number of divisions of the fine tuning dial: 0.183E-3 / 1.6E-5 = 11.4 To decrease the frequency, decrease the dial setting by 11.4. Finally, check the drift rate with the phase meter again to confirm that the drift rate is much lower than before.