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From: Jim Ray (USNO 202-762-1444)
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Subject: [GPST] NPL JPS receiver test
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Date: Tue, 28 Mar 2000 16:40:57 EST
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Forwarded message (for those who do not get IGS Mail):
From: Jon Clarke
To: IGS_IGSMail
Subject: [IGSMAIL-2768]: NPL JPS receiver test
Date: Tue, 28 Mar 2000 16:03:57 +0100
******************************************************************************
IGS Electronic Mail 28 Mar 09:56:30 PST 2000 Message Number 2768
******************************************************************************
Author: Jon Clarke
Subject: NPL JPS receiver test
Dear Colleagues,
recently, with the kind assistance of Javad Positioning Systems, NPL
borrowed and tested a JPS EuroCard receiver to attempt to establish its
usefulness for carrier phase time transfers. I have posted the raw data
and results on an anonymous ftp site (see message below).
The JPS website is http://www.javad.com/ and gives a number of technical
details, including a downloadable version of the GPS receiver interface
language document, which explains the contents of the JPS proprietary
format files.
Please feel free to use this data - I hope it is useful to some of you.
We would appreciate any feedback on the results, or reports on any
problems encountered.
Note that Rinex from our main receiver, NPLB, and CGGTTS common view
data for our R100 GPS/Glonass receiver are also available via ftp
according to instructions listed below the Javad message.
Regards,
Jon
*******************************************
JPSTest ftp
-----------
server: ftp.npl.co.uk
user: anonymous
password: [your e-mail address]
directory: pub\time\jpstest\
Dear Colleagues,
this ftp directory holds the data and analysis resulting from a test of
a Javad Positioning Systems EuroCard receiver at NPL from 1 March 2000
to
21 March 2000. Please feel free to use this data.
The test was an attempt to see whether the JPS receivers are
suitable for use in carrier phase time transfers, and thus to answer the
following points:
1) considering that the receiver does not take a synchronising 1pps,
could the arbitary offset to the reference clock be measured?
2) as the internal clock is disciplined to a reference frequency, could
this disciplining be measured?
3) is there a significantly poor temperature coefficient?
4) what are the effects of power cycles?
I feel the tests have answered these questions reasonably to my
satisfaction.
If you have any questions or comments please contact me (details below).
Comments:
1) to calculate the offset between the UTC(NPL) 1pps and the receiver
internal clock it is necessary to calculate the following:
UTC(NPL) - JPS 3D UTC(NPL) - B5 offset + CT - T0 + ZA
where:
B5 offset 3D offset due to local reconstruction of 1pps in Building
5
(time transfer lab), as UTC(NPL) is in building 2,
3D 8450 +/- 30 ns (exact measurement to be done soon),
stable to <1ns.
CT 3D counter-timer measurement (be careful of signs, as I
triggered from the JPS, not from my reference),
T0 3D JPS reported offset of (internal clock - GPS time),
ZA 3D JPS reported GPS time mod 25 ns, to overcome 25ns hardware
quantisation of 1pps output (which is GPS time).
Derivation:
Denoting -
counter-timer readings CT,
reference time T(ref),
Javad internal clock time T(Javad),
Javad 1pps output time T(out),
GPS time T(GPS),
the quantisation operater qua,
the modulus operator mod,
T(out) 3D T(GPS) qua 25ns 3D T(GPS) + ZA
T0 3D T(Javad) - T(GPS) [this appears to contradict]
[the JPS GRIL document!]
ZA 3D T(GPS) mod 25ns 3D T(out) - T(GPS)
CT 3D T(ref) - T(out)
3D T(ref) - [T(GPS) qua 25ns]
CT - T0 + ZA 3D T(ref) - T(out) - T0 + ZA
3D T(ref) - T(out) - T(Javad) + T(GPS) + T(out) - T(GPS)
3D T(ref) - T(Javad)
3D sync. constant + Javad clock drift
3) JPS proprietary format files: these are ASCII text characters
followed by binary message contents, and must be intepreted in order
to obtain the ~~/RT time-stamp, and T0 and ZA messages.
2) counter-timer measurements: there was a problem with our logging
(due to syncing problems between the time scale generator and the
PC) so some points are missing (there should be one every second).
I am suspicious of the time-stamping on points where there are
problems -
it may be that the stamp shows when the attempt to log a point
started, rather than the 1pps which it actually managed to measure.
There are enough valid points that useful conclusions may be drawn.
Regards,
Jon
0123456789012345678901234567890123456789012345678901234567890123456789
Equipment
---------
JPS Eurocard receiver,
LegAnt antenna,
SR620 ps-resolution counter-timer,
PC to log receiver and counter-timer,
TST/Trak 6460-11 Time scale generator as timing reference for syncing
PC,
reference 1pps, derived from UTC(NPL),
reference 5MHz, derived from UTC(NPL),
Arrangement
-----------
See file Arrangment.gif for how equipment was connected. Also see
existing
equipment arrangement in TTSetup7.gif.
Data
----
1) logging the JPS 1pps output (GPS time qunatised to 25ns) on a
ps-resolution
counter-timer against an NPL reference 1pps.
This allows a measurement of
i) how the receiver internal clock is tracking the external 5MHz
reference.
ii) the arbitrary offset (which changes on each power cycle) between
the
internal receiver clock and the reference 1pps.
2) logging the JPS proprietary format files to
i) form Rinex for submission to the University of Berne for
differential
carrier phase analysis,
ii) obtain the T0 and ZA values that allow the 1pps output to be
corrected to
GPS time, and then internal receiver clock time.
Sub-directory Contents
------------- --------
Rinex Z-compressed compact Rinex format data.
JPS JPS proprietary format binary files. These files are
large, and so I have only placed a selection.
CT Counter-timer measurement files as a zip archive.
These are entirely raw, unprocessed files.
Analysis Excel spreadsheets containing my analysis:
51609_StepByStep.xls shows all relevant data sets, and
how
the residual NPL ref - JPS internal clock may be
calculated.
51614_LocalVsBerne.xls compares the local residuals (with
a 5 minute rolling average to reduce noise), as
calculated
above, against the 5 minute epoch Bernese analysis
results
from Berne for the JPS receiver vs. our reference
receiver
NPLB (Ashtech Z12T), which is locked to UTC(NPL).
51619_TempAndPower.xls shows the effects of two power
cycles
on the arbitrary offset, and the effects of two cycles
of
heating.
51622_WholeDay.xls shows a whole day's residuals.
Author: Jon Clarke, 2000-03-28.
*******************************************
INSTRUCTIONS FOR ACCESSING CTM FTP ARCHIVES
-------------------------------------------
Directions on using our Ashtech data FTP archive
---------- -- ----- --- ------- ---- --- -------
This site holds our Ashtech Z12T geodetic GPS receiver
observation files, in UNIX-compressed compact RINEX format.
Connect to server: ftp.npl.co.uk
Username: anonymous
Password: [your e-mail address]
Move to our archive directory: cd pub/gpsphase
Then there are various useful commands, such as:
List commands: help
List contents: dir
obtain file: get [filename - this is case sensitive]
To leave: quit
Other data available via anonymous ftp
----- ---- --------- --- --------- ---
3S Nav R100-40T common view time transfer data: pub/time/glonass
GPS common view time transfer data (this is used for our routine
link with BIPM to contribute UTC(NPL) to UTC(BIPM)): pub/time/gps
Please contact me if you have any difficulties.
Regards,
Jon Clarke, 1998-02-24.
*******************************************
------------------------------------------------------------------------
Mr Jon Clarke Time and Frequency Section,
jon.clarke@npl.co.uk Centre for Electromagnetic and Time Metrology,
tel: +44 (0) 20 8943 6548 National Physical Laboratory,
fax: +44 (0) 20 8943 6529 Queens Road, Teddington, TW11 0LW, U.K.
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