[time-nuts] Positional accuracy of the M12+T

[Randy Warner]

Magnus et al,

 Attached are a couple of Excel files from some tests I ran about 5
years ago with a UT+ receiver running with a Timing2000 antenna with a
full view of the sky. 

One plot shows the individual error components (X/Y/Z) of the 28 runs,
while the other plot shows the vector magnitudes. 

Note that even with 10,000 samples getting below a 2m 3D error is tough.


Randy Warner
Senior Applications Engineer
Synergy Systems, LLC
randy at synergy-gps.com
________________________________________________________________________
__________________________________________
-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Tom Van Baak
Sent: Thursday, January 04, 2007 11:40 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Positional accuracy of the M12+T

> Tom,
>
> Good points. I think that a lot of people are unaware of the diurnal 
> shifts that occur due to atmospherics. These can be many 10's of 
> noseconds compared to UTC. This is true for every receiver I have ever

> worked with. The ionospheric correction algorithms are good, but they 
> are not perfect. Can't wait for a civilian L2.....................
>
>
> Randy

Right. What gets in the way of accurate UTC time from an M12+, or just
about any other GPS receiver is:
(not in any particular order):

 -- antenna cable feed delays
 -- antenna delays
 -- antenna phase center errors
 -- internal receiver hardware delays
 -- external receiver connector or other cabling delays
 -- trigger level or zero-crossing errors
 -- antenna preamp, RF filter, or splitter delays
 -- humidity
 -- tempco in all of the above
 -- voltco in some of the above
 -- receiver firmware delays
 -- sawtooth errors
 -- 1PPS quantization errors
 -- imprecise zero-D position measurement
 -- PPF (pigeon poop factor ;-)
 -- multi-path errors (large)
 -- GPS SV clock errors
 -- GPS SV ephemeris errors
 -- ionospheric errors (large)
 -- tropospheric errors (small)
 -- UTC(USNO) errors

Some of these vary with ~12 or ~24 hour periods; some of these vary with
1 year periods; some of these show sudden jumps; some of these show
gradual drift; some of these just wander around over time.

You get the idea. Some are ps, ps/K, some are ns, some are tens of ns. I
wish I could give you a nice list with hard numbers but I don't know.
Perhaps Tom Clark does?

I also don't have any data to back up this bold claim, but: I would be
surprised if any of us, me included, has UTC at home closer than maybe
20 to 50 ns. -- with the exception of DougHo (with his USNO calibrated,
real-time JPL corrected, frequency-steered, 5071A-driven,
post-processed, dual frequency Z12T) and the one or two of you on the
list that work at TSC.

What most of us time-nuts use GPS receivers for is quartz, rubidium, or
eBay-cesium *frequency* measurements, and so all these fixed, or slowly
varying *time* offsets, have little or no effect on our measurements.

/tvb
http://www.LeapSecond.com



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