On 08/22/2012 01:22 AM, Edgardo Molina wrote:
b. Is it possible to build a GPSDRb? I would like to know if it is reasonable to pursue the goal to discipline the 5065a with a TB which I also got recently.
Some Rbs have a "C-field" input that can technically be used to discipline it, but this is not the approach I am going to take with mine. A Rb oscillator is internally an OCXO that is disciplined to the Rb physics package, with the goal of holding a frequency over a long period of time with the only variance coming from deficiencies in the measurement circuitry. Using the C-field to discipline it is kind of throwing out the long-term stability characteristics of the Rb and using it as an expensive OCXO. It's more interesting to me as a holdover source for a conventional GPSDO.
The design I'm thinking of is to have a separate microcontroller clocked by the Rb that will generate a third pulse-per-second (the first two being the raw one from GPS and the divided-down local oscillator). As long as the GPS is locked the divider will not output pulses but will monitor the pulses from the local oscillator and use it to count the frequency of the Rb. Once lock is lost or holdover is manually engaged, then it stops counting and starts outputting pulse-per-second based on the last known average frequency it counted. The GPSDO would then continue normal disciplining based on the Rb pulses until GPS lock returns. Of course while locked the measured frequency would also be reported so that the Rb could be calibrated in situ.
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