[time-nuts] is there a "best bet" advanced hobbyist buildable GPSDOdesign?

Scott Burris slburris at gmail.com
Thu Dec 13 12:00:32 EST 2007

Bruce Griffiths wrote:
> On checking the Mouser and Digikey websites the DS1020 series
> programmable delay lines are non stock items.
> However I can obtain the DS1020-25 locally from RS Components.
> The D1020-15 would be preferable for use with an M12M GPS timing
> receiver, however the DS1020-25 could be used.
> Maybe we need to consider using a CPLD or another implementation (eg
> ramp generator plus DAC (8bit) and comparator).
> Analog Devices used to make a single chip implementation of the ramp
> plus DAC and comparator programmable delay system.
> However such devices need to be calibrated, preferably continuously.
> The saving grace is that with a dedicated processor, there's plenty of
> time and processing power to do this once a second (between successive
> PPS pulses).
> Calibration technique is simple:
> 1) Adjust the programmed delay so that the programmed delay is exactly 1
> (OCXO) clock period record the DAC data required to achieve this.
> 2) Adjust the programmed delay so that the programmed delay is exactly 2
> (OCXO) clock periods, record the DAC data required to achieve this.
> 3) calculate the OFFSET and GAIN parameters from the above data.
> Of course such a scheme can be elaborated to include delays greater than
> a couple clock periods and exponential averaging of results can be
> employed to reduce the noise.
> The calibration technique assumes that the delay is a linear function of
> the DAC input.
> A D flipflop plus some additional logic (synchroniser) can be used to
> detect coincidence between the clock edge and the output of the delay
> device.

Continuing the design discussions, anyone have opinions about powering 
the HP 10811 oscillator?
I'm thinking that you want voltage regulators that are pretty quiet so 
as to minimize jitter introduced
via the power supply.  To that end, I'm looking at a LT1761 for the +12v 
OSC voltage and an LT3080
for the 24v heater supply. 

In reading the 10811 manual, the heater and oscillator are isolated, yet 
the example power supply ties
both together in a common ground.  That certainly would make things 
simpler, as a 24VCT transformer
could be used, and +12 and +24 volts could be made pretty naturally that 

How important in a GPSDO application is it to keep these two sections 
completely isolated?  I figure I would
either have to use a small HF transformer with a chopper circuit or a 
separate 60hz transformer for the second


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