[time-nuts] Anyone want an engineering job making a GPSDO comparator for T-Bolts?
Charles Steinmetz
csteinmetz at yandex.com
Sat Nov 9 00:07:26 EST 2013
Bob wrote:
>We successfully "replaced" an internal low-quality TCXO with an external
>T-Bolt signal with much help from Time Nuts; but one guy called me up and
>suggested we discipline the INTERNAL oscillator instead of replacing it with
>an external signal.
Whether or not this is a good idea depends entirely on your
particular needs. A GPSDO works by relying on the quartz oscillator
for stability at low tau, and the GPS for stability at higher
tau. In the case of a quartz OCXO, the crossover generally occurs
between perhaps fifty and several hundred seconds. If you need good
stability at tau < 100 seconds, where the GPS is not very stable, the
disciplined TCXO may be much worse than the disciplined OCXO (both
because the oven stabilizes the crystal better, and because OCXOs
generally use better crystals in the first place). When excellent
stability at tau < 100 seconds is required, you would likely find the
disciplined TCXO inferior to a disciplined OCXO.
This is not to say that disciplined TCXOs are necessarily junk --
Jackson Labs makes some that reportedly perform fairly well -- but I
suspect JL uses better TCXOs than the ones you usually find. Even
so, their disciplined TCXOs are not as good as their disciplined OCXOs.
Best regards,
Charles
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