GPS position
Now that I have three (maybe four) working GPSDO's, I'd like to set
the GPS coordinates the same on all of them. The survey that each one
does produces very similar coordinates, but not exactly the same.
The Z3801A's have VP's, the Lucent has a UT+. I don't know what is in
the 58540A, as the manual doesn't say and the :DIAG:IDEN:GPS? command
isn't supported.
Would using a modern GPS, like a uBlox, and averaging for quite a
while produce acceptable coordinates to manually enter into all of the
GPSDO's? Of course the uBlox would be on the same splitter and antenna
as the other units during the averaging.
Joe Gray
W5JG
In message CAF7oPz3KxSA-Vde80PxHzbPWYBwSiU-nRzYQBvh+5obu8t7ejQ@mail.gmail.com
, Joseph Gray writes:
Would using a modern GPS, like a uBlox, and averaging for quite a
while produce acceptable coordinates to manually enter into all of the
GPSDO's? Of course the uBlox would be on the same splitter and antenna
as the other units during the averaging.
So I played with this a long time ago, and massively averaging still
does not give you the coords you want, because they are affected
by the same disturbances you want to eliminate.
A better strategy is to stare at the residuals for each satelite and
see where to move:
http://phk.freebsd.dk/raga/sneak/
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Since, I assume, you are most interested in time/frequency I recommend you
use the position that each device self determined. To verify the 10 Mhz
output it is easy to compare one against the other. If you don't have a
frequency meter with enough digits, just use a 'scope syncing on one and
see if the other trace is stable over time.
The other thing that comes to mind: were all GPSDOs taking the measurements
at the same time? If not, you should EXPECT different positions to be
reported (within the specifications of the receiver)
Michael/K7HIL
On May 2, 2016 4:03 AM, "Joseph Gray" jgray@zianet.com wrote:
Now that I have three (maybe four) working GPSDO's, I'd like to set
the GPS coordinates the same on all of them. The survey that each one
does produces very similar coordinates, but not exactly the same.
The Z3801A's have VP's, the Lucent has a UT+. I don't know what is in
the 58540A, as the manual doesn't say and the :DIAG:IDEN:GPS? command
isn't supported.
Would using a modern GPS, like a uBlox, and averaging for quite a
while produce acceptable coordinates to manually enter into all of the
GPSDO's? Of course the uBlox would be on the same splitter and antenna
as the other units during the averaging.
Joe Gray
W5JG
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A man with a GPS knows where he is. A man with two GPS' not not sure.
I've always wanted to walk my self-survey GPS over to a brass USGS
benchmark and see it the GPS matches to benchmark location. OK, I've done
this with a hand held GPS and gotten readings within about 10 meters.
But before spending a lot of time removing the lat 10cm of error I'd do a
test at the nearest BM that is not in the middle of a street.
What has stopped me from doing this is that a few years ago I had to have
my lot lines surveyed. They got to better then 1/10 of a foot at each
corner and shot some brass markers into the concrete. Google can see my
house's roof ridge lines and the concrete so I can work out the exact
location of the roof mount antenna to within maybe 18 inches. It seems to
agree with the survey as long as everyone uses WGS84.
On Sun, May 1, 2016 at 11:44 PM, Joseph Gray jgray@zianet.com wrote:
Now that I have three (maybe four) working GPSDO's, I'd like to set
the GPS coordinates the same on all of them. The survey that each one
does produces very similar coordinates, but not exactly the same.
The Z3801A's have VP's, the Lucent has a UT+. I don't know what is in
the 58540A, as the manual doesn't say and the :DIAG:IDEN:GPS? command
isn't supported.
Would using a modern GPS, like a uBlox, and averaging for quite a
while produce acceptable coordinates to manually enter into all of the
GPSDO's? Of course the uBlox would be on the same splitter and antenna
as the other units during the averaging.
Joe Gray
W5JG
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--
Chris Albertson
Redondo Beach, California
Nothing to do with time but...
Technically speaking, in surveying a bench mark is a vertical control point. In
playing with Geocaching I've located bench marks that were placed in the 1930's
and never found again (until I did). There were often a hundred feet or more
from where the description had them. (Great fun BTW)
See: https://www.geocaching.com/mark/
On 5/2/2016 9:13 AM, Chris Albertson wrote:
A man with a GPS knows where he is. A man with two GPS' not not sure.
I've always wanted to walk my self-survey GPS over to a brass USGS
benchmark and see it the GPS matches to benchmark location. OK, I've done
this with a hand held GPS and gotten readings within about 10 meters.
But before spending a lot of time removing the lat 10cm of error I'd do a
test at the nearest BM that is not in the middle of a street.
What has stopped me from doing this is that a few years ago I had to have
my lot lines surveyed. They got to better then 1/10 of a foot at each
corner and shot some brass markers into the concrete. Google can see my
house's roof ridge lines and the concrete so I can work out the exact
location of the roof mount antenna to within maybe 18 inches. It seems to
agree with the survey as long as everyone uses WGS84.
On the topic of benchmarks, I found this official site earlier this morning.
http://www.ngs.noaa.gov/CORS-Proxy/NGSDataExplorer/
Joe Gray
W5JG
On Mon, May 2, 2016 at 1:49 PM, Wes wes@triconet.org wrote:
Nothing to do with time but...
Technically speaking, in surveying a bench mark is a vertical control point.
In playing with Geocaching I've located bench marks that were placed in the
1930's and never found again (until I did). There were often a hundred feet
or more from where the description had them. (Great fun BTW)
See: https://www.geocaching.com/mark/
On 5/2/2016 9:13 AM, Chris Albertson wrote:
A man with a GPS knows where he is. A man with two GPS' not not sure.
I've always wanted to walk my self-survey GPS over to a brass USGS
benchmark and see it the GPS matches to benchmark location. OK, I've done
this with a hand held GPS and gotten readings within about 10 meters.
But before spending a lot of time removing the lat 10cm of error I'd do a
test at the nearest BM that is not in the middle of a street.
What has stopped me from doing this is that a few years ago I had to have
my lot lines surveyed. They got to better then 1/10 of a foot at each
corner and shot some brass markers into the concrete. Google can see
my
house's roof ridge lines and the concrete so I can work out the exact
location of the roof mount antenna to within maybe 18 inches. It seems to
agree with the survey as long as everyone uses WGS84.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hi
The “real” answer is to beg / borrow / obtain a geodetic receiver and let it run for an
hour or ten at your location. Unless you are really out in the middle of nowhere, that
will give you a very accurate position. If you don’t have any buddies who are surveyors,
they do show up on eBay at < $300 sort of prices (with antenna) from time to time.
As always, there is a point of “that’s probably good enough”. For various reasons, vertical
errors are not going to be quite as important as horizontal errors. If you figure 3 ns / meter
horizontal and allow a bit more than that vertical … you are doing what most people do. Once
you get the geometric error under 1 ns, you probably are at 1/10 the other errors you see
over a 24 hour period on L1, under good conditions. If the ionosphere is acting up, things
could be much worse.
Bottom line: If your estimates are within a foot of being correct, that’s probably
good enough. Looking at the raw data is always a good idea. Things like multi path
can really skew a bulk average …
Bob
On May 2, 2016, at 2:44 AM, Joseph Gray jgray@zianet.com wrote:
Now that I have three (maybe four) working GPSDO's, I'd like to set
the GPS coordinates the same on all of them. The survey that each one
does produces very similar coordinates, but not exactly the same.
The Z3801A's have VP's, the Lucent has a UT+. I don't know what is in
the 58540A, as the manual doesn't say and the :DIAG:IDEN:GPS? command
isn't supported.
Would using a modern GPS, like a uBlox, and averaging for quite a
while produce acceptable coordinates to manually enter into all of the
GPSDO's? Of course the uBlox would be on the same splitter and antenna
as the other units during the averaging.
Joe Gray
W5JG
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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