[time-nuts] Advise on building a DIY GPSDO?

Bob Camp kb8tq at n1k.org
Tue Apr 5 22:29:05 UTC 2016


Hi

Building a GPSDO *after* you have a lab full of gear is a very different proposition than
building one because cash is tight and nobody mentioned the $43 surplus units. 

There’s no right and wrong here, just a need to look at “why?” before you get going. 

Bob

> On Apr 5, 2016, at 5:40 PM, Chris Albertson <albertson.chris at gmail.com> wrote:
> 
> Thank you, My goal was to build the simplest and lowest cost GPSDO that
> could still work.   The major cost item was the $20 crystal oscillator I
> bought on eBay and a $19 Motorola "Oncore" 8 channel GPS Receiver.  The
> rest of the stuff cost about $5.   I don't count the cost of the GPS
> because it was already driving NTP.   SO I'd calling it a $25 GPS.  It's
> performance is acceptable to driving the 10MHz input of a basic frequency
> counter.
> 
> I already owned a T-Bolt and an Rb oscillator and a few counters and dual
> trace scope.  So I compare the $25 unit to the t-bolt and see it drifts off
> a tiny bit then the software seethes and pushes it back.   If I know more
> about running PID controllers it would work better.
> 
> Lars W. actually did the design and posted it here.  I build most of his
> design, leaving some stuff out and rewrote all the software to be about
> 1/20th as many lines of code.  My goal was to be as simple and cheap as
> possible.
> 
> I think if the goal is to build something and the learn how it works, build
> a VERY simple device then in a series of tiny "baby steps" improve it.
> 
> If I ever get around to it.  I will add my $35 surplus Rb unit to the same
> cheap Arduino.  It should work will.  I can do hours/days integration
> times.  The Rb has a digital only freq. adjustment that has steps of about
> 10E-11 or so.  All I need is to keep it on the correct step.
> 
> Another reason to build rather than buy is because you want something that
> you can't buy.  That will be my next GPSDO.  I want a "good" crystal and an
> internal Rb standard that can be used when GPS is not available (for
> portable use) and I want it to run on common LiPo batteries used for power
> tools.  The idea is that when it is at home I plug in the 1PPS cable and
> the units "syncs" to GPS and the Rb is put in frequency.   I may never get
> around tooth's as the Rb is very good all by itself to the limit of my
> ability to measure it.
> 
> 
> 
> 
> On Mon, Apr 4, 2016 at 12:00 PM, Chris Caudle <chris at chriscaudle.org> wrote:
> 
>> 
>> 
>> want to build next, then go ahead and have fun.  Chris Albertson's arduino
>> based design is probably as good a place to start as any, it should be
>> cheap and I think the pieces are easier to find than that CPLD based
>> design that relies on having a GPS that can output 10kHz instead of just
>> PPS.
>> 
>> --
>> Chris Caudle
>> 
>> 
>> 
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> 
> 
> 
> -- 
> 
> Chris Albertson
> Redondo Beach, California
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