[time-nuts] making most of SRS Rb source

Tim Natusch tim.natusch at aut.ac.nz
Wed Jan 18 23:21:22 EST 2006

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 Natusch
Senior Lecturer
Electrotechnology Dept.

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