[time-nuts] Disciplining Rubidium
Tom Van Baak
tvb at LeapSecond.com
Thu Apr 24 17:56:16 EDT 2008
> There's no particular reason that a GPS carrier phase disciplined OCXO
> need be particularly expensive unless of course it incorporates an
> Oscilloquartz 8607 with ultra low adev specs.
> Suitable receivers seem to be readily available. The only major
> complication is the need to phase lock their local oscillator to the
> OCXO being disciplined.
Can you explain this a bit more? I know you often mention
this point. But it seems there must be something more to it;
otherwise we all would have seen low-cost carrier-phase
GPSDO products on the market over the past 15 years...
Instead there are only a few, they are all very expensive,
and none (?) of them use standard OEM GPS receivers.
I ran a carrier-phase Ashtech Z12T here for a while. It was
my understanding that the reason it performed so well was
a combination of carrier-phase tracking, L1/L2 choke ring
antenna, phase stabilized cables, and dual band receiver.
It also required an external free-running 20 MHz laboratory
reference (I used a 4x multiplier off a cesium or maser).
Further, one used it by collecting raw RINEX data and daily
sent the batch files to be post-processed for two weeks.
It would be interesting to know how much each of these five
pieces contributed to its overall performance. My hunch is
cheap OEM timing receiver carrier-phase measurement
alone is not enough.
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