I have recently been involved with VLBI observations between NZ and Australia. We used the SRS FS725 as our Freq. standard here in NZ. We can not afford a Hydrogen Maser as yet! The FS725 uses the PRS 10 Rb package but adds interface electronics that amongst other things adds the ability to control the time constant of the loop used to discipline the Rb from an external 1 PPS source. We used GPS (Trimble Thunderbolt) to derive the 1 PPS signal and a loop constant of 2.5 hrs. This gave a reasonable compromise, controlling the long term drift of the Rb without being too destructive of the basic short term behaviour (there are noticeable effects though). We were successful with our VLBI observations with this setup. It is probably still not optimal but works. I have data gathered from a direct comparison of this setup and the Hydrogen Masers at the University of Tasmania and Parkes Radio Observatories. Have not yet had a chance to do much detailed analysis on it.
Tim Tim Natusch Senior Lecturer Electrotechnology Dept. AUT _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
