[time-nuts] Common-View GPS Network

Wed Apr 17 00:17:24 EDT 2013

A few reasons:

    - I am interested to see what can be done with the statistics of an ensemble of oscillators---in particular, whether the additional measurements can be used to get a timescale that is more stable than just GPS and OCXO or Rb.

    - To produce some data that could be used for modelling other systems. 

  - If the first point plays out, then to allow access to a more accurate timescale by amateurs who cannot justify 15k/yr for NIST's.

It might be interesting to see if one could extract ionospheric data from the ensemble too.

I've just started a Ph.D, so my free time is such that it will probably be a while before I can get anything running, but I'd like to see what can be done regardless, if only so that three years of statistics doesn't drain away what little timing knowledge I've managed to accumulate. 

Thanks, 
Lachlan Gunn

-------- Original message --------
From: Mark Spencer <mspencer12345 at yahoo.ca> 
Date:  
To: time-nuts at febo.com 
Subject: Re: [time-nuts] Common-View GPS Network 

Just curious what would a typical use case for this network be ?  My limited understanding of common view GPS in this context is that it can be used for time (and frequency) transfer between labs.

Thanks in advance for any replies.

Regards
Mark Spencer

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Message: 6
Date: Tue, 16 Apr 2013 15:53:09 +0200
From: Achim Vollhardt <avollhar at physik.uzh.ch>
To: time-nuts at febo.com
Subject: Re: [time-nuts] Common-View GPS Network
Message-ID: <516D57C5.9070304 at physik.uzh.ch>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Count me in as well, if you need another participating station. I have 
my Thunderbolt running 24/7 with a solid stationary antenna..

Achim

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Message: 7
Date: Tue, 16 Apr 2013 08:00:39 -0700
From: "WarrenS" <warrensjmail-one at yahoo.com>
To: "Discussion of precise time and frequency measurement"
    <time-nuts at febo.com>
Subject: Re: [time-nuts] Common-View GPS Network
Message-ID: <E466FE7AD5B9476DB5F8199B1B3CFCBE at Warcon28Gz>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
    reply-type=original

"is one better off just taking the simple route and tracking GPS time 
directly?"
My response is Yes, as long as you use the GPS to discipline a good 
Oscillator.

GPS on its own is generally capable of about 10 ns of phase error, pretty 
much over any time period.
So the longer you average the closer you know the frequency.
I did some remote common view experiments a while back to see if I could 
find a way to improvement a GPSDO using low cost dual common view GPS.

I used Tbolt GPSs, because they are capable of more than a decade better 
performance than the 1 ns (with correction) GPS engines (*).
For monitoring I used Lady Heather so I could control and get real time data 
from the remote GPS.

After several unsuccessful test using various remote locations,
I got smarter and  moved the "Remote" GPS under the same roof to see what 
the limitations where.

I found the limitation was in my Antenna. (a  58532A type).
That is when I used two antennas, even with everything at the same location, 
taking common view differences added noise.
The only way I was able to improve the noise was to use the same GPS signal 
thru a splitter going to both GPS.
Not real useful for "remote" Common View, so my experiment turned into a 
dual Tbolt DMTD.

For some post I did, see Time Nuts back in Oct of 2011 from "WarrenS" and 
"ws at Yahoo"
"Common View Tbolt-Tic",  "DMTD using TBolts" and "Measuring ADEV using 
TBolt-Tic tester"

(*) The TBolt Engine is capable of 1e-11 at 3 seconds.
and 1e-12 ADEV at 300 seconds using the difference between two TBolts driven 
with a common GPS signal, see:
<http://www.febo.com/pipermail/time-nuts/attachments/20111023/c84deb5b/attachment-0001.gif>

ws

*********************
Hello all.

Having spent some time working over the last year on GPS time stability
measurement, I'm keen to move onwards and upwards and have a go at
common-view time transfer.  While my receivers are in the post, I have
thinking about my next direction.  One thought that I have had is to try to
write some software that can be used for real-time common-view (public if
there is interest, but I am getting ahead of myself I think).

My question to those in the know is whether they have found common-view to
be useful over medium timescales (say, an hour or four).  My understanding
is that after a day or so the GPS signal itself becomes usable as a
standard, so building a network is probably not tremendously useful over
these sorts of time periods, but looking at such as figure 6 of [1],
common-view should still be useful between a few minutes and hours.  Has
anyone here tried using such a method to produce their own short-term time
scale, or is one better off just taking the simple route and tracking GPS
time directly?

Thanks,
Lachlan

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