[time-nuts] GPS position

Bob Camp kb8tq at n1k.org
Mon May 2 18:34:16 EDT 2016


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 at 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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