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Re: Questions (Answered)

From: Gary E. Miller
Subject: Re: Questions (Answered)
Date: Wed, 22 Jun 2022 21:19:20 -0700

Yo Ken.Hendrickson---!

On Wed, 22 Jun 2022 21:17:30 +0000
Ken.Hendrickson--- via <> wrote:

> I have found more information that answers most (if not all) of my
> questions.
> The gpsd.8 man page indicates that gpsd can use the Zodiac binary
> data.

Yup.  But.  I have never seen a Zodiac, and I don't think they have been
made in over a decade.  The one and only Zodiac regression test we
have is from 2005.  There may be some bit rot.

> Austin's Nerdy Things describes a microsecond accurate solution on a
> Raspberry Pi w/ 1PPS.

That should be easy.

> Finally, I found these IETF documents:

gpsd implements that.


The Linux kernel implements that.

Check out the Timeserver HOWTOs hereO:

> This will give me a stand-alone time-frequency standard that will
> work as long as GPS is available. Differential GPS would hold no
> value for me, nor be practical if using the system portable or mobile.

No need for DGPS if 1 micro second is your goal.

> This web page shows pictures of some of the components (OCXO, Jupiter
> GPS, PLL board, PLL board schematic):

Wow, steampunk!

> Can gpsd read the proprietary Zodiac binary message format?  If not,
> I could write that software.  Apparently, the time mark message which
> precedes the 1PPS pulse is only output in the 9600 bps binary message
> format, but not 4800 bps NMEA.  (The UTC Time Mark pulse output
> message provides the number of seconds since the beginning of the
> week, about 0.5 second before the 1PPS signal.)

gpsd PPS can work fine with NMEA or Zodiac binary.

> What is currently the best way to utilize the 1PPS signal?

The ppscheck program from gpsd.

> Using the 1PPS signal seems to require being able to read the
> proprietary Zodiac binary message format.

No.  But you'll get more data with the Zodiac binary.

> One objective I have, if possible, is to have a stand-alone time
> server with no internet connection.  Is this possible?  What would
> the gpsd requirements be?


> Does anybody use differential GPS?


>  What would be required?


> Would
> differential GPS only improve the geolocation solution, or would it
> also improve a time solution?

It improves both.  With GNSS time == position.

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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703  Tel:+1 541 382 8588

            Veritas liberabit vos. -- Quid est veritas?
    "If you can't measure it, you can't improve it." - Lord Kelvin

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