[time-nuts] Leap Second results: cheap GPS/1PPS receivers

[Tom Van Baak]

Hi Bob,

For precise timing we use the 1PPS output of a GPS receiver. And yes, it is typically extremely sharp and precise. If you want 1 MHz or 10 MHz then you need all the complication of a disciplined oscillator. But the timing itself comes from the receiver's 1PPS pulse. Even without accurate survey or position hold mode or sawtooth correction, a plain, cheap GPS/1PPS receiver makes a superb long-term accurate time source.

In this example of a cheap GPS 1PPS (http://www.leapsecond.com/pages/MG1613S/), the risetime was 2 ns. The rms jitter was 22 ns. This is more than enough for a 5328A to fully calibrate any OCXO. Just use the 1PPS and a 1 or 10 MHz OCXO as the start and stop channels in TI mode and record the gradual drift of phase between them. Programs like TimeLab will handle the occasional 1 us or 100 ns phase wrap. Use something like 1 VDC trigger for the 1PPS and 0 VAC for the OCXO trigger. A rule-of-thumb is that if it drifts 1 us over a day the frequency offset is 1e-11

/tvb

  ----- Original Message ----- 
  From: Bob Albert 
  To: Tom Van Baak ; Discussion of precise time and frequency measurement ; Discussion of precise time and frequency measurement 
  Sent: Wednesday, July 01, 2015 10:55 AM
  Subject: Re: [time-nuts] Leap Second results: cheap GPS/1PPS receivers


  I am missing something here.  How does one use a 1 PPS signal? I see how I can use a 1 MHz or 10 MHz for a time standard but the 1 PPS usage eludes me.  Unless the pulse is extremely sharp, a minor uncertainty in the shape or amplitude will have profound effects on the timing.


  I use an HP 5328A with the OCXO and wonder how I can improve its accuracy.


  Bob






  On Wednesday, July 1, 2015 10:01 AM, Tom Van Baak <tvb at LeapSecond.com> wrote:




  I logged NMEA from three cheap ($15-$50) GPS/1PPS receivers, the kind popular with hobbyists: parallax(good), reyax(good), adafruit(bad).