I had to build a DC amplifier to interface the 5x10-10 rubidium sensitivity to the 7.5x10-9 controller sensitivity. Basically a gain of X15 was needed. Brook’s controller has several PI filters and the data I will report is in the longest PI constant, running in mode 7.
A 1 second Allan variance was recorded as 1.71x10-10, with a Maximum Time Interval Error (MTIE) of 37 nS per 24 hours. 10 seconds was 7.55x10-12, MTIE 28 nS. 100 seconds was 1.5x10-12 MTIE 29 nS. 1000 seconds was 1.65x10-12, MTIE 28 nS. 10,000 seconds was 1.69x10-13 32 nS. I used another rubidium for reference when recording the 1 to 1000 second measurements, and from 100 to 10,000 seconds, I used a Z3801A for reference. Sure wished I had a cesium to compare too! I used a Motorola M12+ GPS receiver as the 1 PPS source for the Shera controller.
Brook’s normal controller updates the rubidium’s EFC every 30 seconds. I believe that is too fast for the unit. He has programmed a new PIC for me that updates at a 120 second rate. Testing is in progress with the new unit and it will take about 30 to 45 days to run all the tests that I require for comparison.
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