[time-nuts] GPSDO Alternatives

dlewis6767 dlewis6767 at austin.rr.com
Fri Dec 7 02:42:45 UTC 2012

Perhaps this is all coming full circle.  As more experience herein shows use of the 1-pps from the gps module is valid, that opens the door to many more cheap GPS modules available than just a few that have 10 KHz also.

Some of the low-cost GPS modules have the 1-pps associated with UTC (accurate), ...many do not.  It depends on what their original purpose was.  Many were used for 'cheap' navigation devices, ...not intended for timing.  Accuracy is on the order 10 to even 100 microseconds.

It then seems to me a simpler state machine, driven by the gps 1pps could be designed.  It could run at 2hz and have 6-to-10 states, as many as needed.  Need to get out the old Karnaugh map book.

  a.. Reset, open counter gate, count two seconds, close counter gate, load dac with overflow/underflow, switch dac output to EVC cap, start over.


From: "Chris Albertson" <albertson.chris at gmail.com>
Sent: Thursday, December 06, 2012 6:30 PM
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Subject: Re: [time-nuts] GPSDO Alternatives

> On Thu, Dec 6, 2012 at 4:09 PM, dlewis6767 <dlewis6767 at austin.rr.com> wrote:
>> could you not add just a little 'glue' outside the uP to relieve it a tad.
>> Let the GPS' 1pps gate some ttl counters and then read for overflow or
>> underflow after xxx seconds.  Have the uP determine  dac correction setting
>> back to the TXCO.
> That is why my first post was to ask "What is the simplest phase defector
> that can work?"   I think you only need a one-bit counter.  A flip-flop
> will do that.   The FF is a classic phase detector used in many PLL
> -- 
> Chris Albertson
> Redondo Beach, California
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