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

[Scott Burris]

Bruce Griffiths wrote:
>
> As far as I know Dallas/Maxim appears to be the only source of suitable
> affordable programmable delay chips for this particular application.
> In principle one could use a tapped chain of gates in a CPLD, however
> continuous calibration of the delay is required (a delay locked loop
> controlling the gate propagation delay by adjusting its power supply
> voltage to compensate for the effect of temperature variations is one
> technique). However unless the Dallas chips become hard to obtain its
> probably best to leave this as a backup option.
>   
What about sending the 1PPS signal through a number of HC family gates 
and using a mux
to select a tap -- is that better than using a CPLD? Hmm, probably the 
delay varies too much from manufacturer to manufacturer
to make this work reliably.  Probably temperature sensitive too.

What kind of delay characteristics are needed?  I see some other delay 
lines with 100ps
steps available, see:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=408-1127-ND

and put that through a mux?

Looks like some of the DS1020's are available through Maxim's e-commerce 
site, but some have
a 15 week lead time, depending on the particular model.
> What processor are you intending to use to decipher the sawtooth
> correction messages from the GPS timing receiver?
> You could use an inexpensive microprocessor dedicated to this simple task.
> Another microprocessor can be used to discipline the OCXO.
> Depending on your experience, this can be easier than using a single
> microprocessor to do everything.
>
>   
I have experience with PICs, Atmel AVRs, and various ARM flavors, and 
limited experience
with SOC processors in Xilinx FPGAs (Picoblaze and the like).  PICs and 
AVRs are cheap, so no problem
dedicating one to this task.

Anyone have a list of GPS units which provide sawtooth correction data?  
I have a few flavors of
Motorola products and a Trimble Lassen IQ laying around.  They all 
provide 1PPS signals, but I bet
some don't have the necessary features.

Scott