[time-nuts] Common-View GPS Network

WarrenS warrensjmail-one at yahoo.com
Tue Apr 16 15:00:39 UTC 2013


"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



 




More information about the Time-nuts_lists.febo.com mailing list