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

Tom Clark, K3IO k3io at verizon.net
Thu Dec 13 13:19:59 EST 2007

Bruce Griffiths wrote:
> Data delay devices (http://www.datadelay.com) also do programmable delay
> lines their minimum order is $US75 which isnt too bad particularly if
> more than one sawtooth corrector is to be built.
> They even do ECL programmable delays as do Micrel (http://www.micrel.com).
> However these ECL programmable delay devices dont have enough range for
> this application.
There is also a good programmable delay line from Dallas/MAXIM that is
less expensive (see http://www.maxim-ic.com/appnotes.cfm/an_pk/107).
Rick Hambly uses the DS1020-015 in his CNS Clock (see
http://www.cnssys.com). See slides 20, 26, 29 & 30 at
http://gpstime.com/files/tow-time2007.ppt for some details.

One comment on the Dallas/MAXIM DS1020 parts: we (Rick & I) found that
Motorola (in the M12 GPS receiver) and Dallas (in the delay line chip)
have a slightly different (~10%) definition for the nanosecond; it
appears to us that the Dallas/MAXIM definition is wrong, and the same
error shows up in many samples. Rick now uses the 150 psec/step Dallas
chip after finding that the ½ & 1 nsec versions had a scale error (see
slides 16-18 in ftp://ftp.cnssys.com/pub/PTTI/PTTI_2006.ppt which
represents slightly earlier work than presented at the 2007 TOW). The
"true" scale factor with the ~10% correction is contained in a look-up
table that converts the M12M binary sawtooth error output into the value
sent to the delay line.

Season's Greetings to all -- Tom

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