[time-nuts] Terrestrial Tides and Land Movement

[Bob Stewart]

Hi Tom,
I'm not sure what you mean by this 0D vs 3D.  I'm using an LEA-6T.  There are three time transfer modes 0=disabled, 1=survey-in, 2=fixed mode.  Are you suggesting that I set it to disabled to run a test?  I've never tried that.  I know that if I monitor the output while doing a survey, the phase is all over the place.
I'm in the middle of a therm correction test at the moment, but the plots at the link below are essentially where I am in development.  The PRS-45A is driving the reference and start inputs of the 5370A.  I'm using a somewhat modified PID system.

http://evoria.net/AE6RV/Status/

Development is essentially over, at this point except for details, like adding code for the M12+ receiver.  I can post a link to the schematic, if there's interest, but I've decided that the code will remain proprietary.  This has turned into something a lot bigger than a $25 GPSDO engine.

Bob
      From: Tom Van Baak <tvb at LeapSecond.com>
 To: Discussion of Precise Time and Frequency Measurement <time-nuts at febo.com> 
 Sent: Monday, May 25, 2015 3:09 PM
 Subject: Re: [time-nuts] Terrestrial Tides and Land Movement
   
Hi Bob,

You only need a survey if your timing receiver is running in zero-D mode. If you move the antenna more than some practical threshold you should adjust the fixed position or maybe just do another survey.

If you plan to move a lot, or if your application is mobile, or are on a slippery slope, or you just don't want to bother with a time-consuming survey, then run the timing receiver in 3D mode. As I said it will perform "almost as well". If you normally get, say 9 SV, I predict the timing accuracy difference is maybe only 10 or 20%.

You're still building a homebrew GPSDO, right? Collect a day of performance data in 0-D and then a day in 3-D and see what difference there is in RMS timing residuals (or in ADEV). I wonder if your GPSDO can even measure the difference.

/tvb

----- Original Message ----- 
From: "Bob Stewart" <bob at evoria.net>
To: "Discussion of Precise Time and Frequency Measurement" <time-nuts at febo.com>
Sent: Monday, May 25, 2015 11:09 AM
Subject: Re: [time-nuts] Terrestrial Tides and Land Movement


Tom said: "The nice thing about GPS, unlike other time transfer methods, is that can handle the case of a moving antenna. As the antenna moves so does the time. This is why GPS timing receivers work (almost as well) on top of your car as on top of your house."
I don't get that. What's the purpose of doing a survey when you move your antenna if this the case?
Bob

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