[time-nuts] "GPS once a day issues" ?

Bob Stewart bob at evoria.net
Mon Oct 20 02:18:30 UTC 2014


Hi Bob,

This multiple antenna issue is one I've been wanting to ask about, as well.  I've got a GPS Source MS14 splitter (right place at the right time) so I don't specifically use multiple antennas.  But, I've got the one still in the attic (disconnected) and the current one I put on the eave on the south side of the house.  Those are both $5 powered pucks from ebay.  I've also got a couple of Adafruits with the built-in antenna laying around.  Do I really need to worry about the interaction of those antennas?  I didn't get a feel for the spacing of interaction from previous posts on the  subject.  They're all at least 10 ft away from each other.

FWIW, I only have one receiver hooked up to the splitter at the moment, and I do not have any terminators on the SMA ports as I don't think they're needed.  The splitter has its own power supply.  I'm only using the ports that are DC isolated from the antenna.


Bob



________________________________
 From: Bob Camp <kb8tq at n1k.org>
To: Bob Stewart <bob at evoria.net> 
Sent: Sunday, October 19, 2014 9:01 PM
Subject: Re: [time-nuts] "GPS once a day issues" ?
 

Hi

One of the reasons you want to wide space antennas if you are putting up more than one it a *hope* that worst case on one will not be identical to worst case on the other.

The other way you can catch the problem is to simply look at what you loop is doing. If it does exactly the same “bump” every night at about 3AM…..

Bob




> On Oct 19, 2014, at 9:58 PM, Bob Stewart <bob at evoria.net> wrote:
> 
> Hi Bob,
> 
> OK, it sounds like something that would not be clearly noticeable with the equipment I have.  I haven't run many multi-day tests, so that's another handicap on this end.  Still developing and testing, but things are looking better than the last time I spoke about my unit.
> 
> thanks,
> 
> Bob
> 
> From: Bob Camp <kb8tq at n1k.org>
> To: Bob Stewart <bob at evoria.net>; Discussion of precise time and frequency measurement <time-nuts at febo.com> 
> Sent: Sunday, October 19, 2014 8:50 PM
> Subject: Re: [time-nuts] "GPS once a day issues" ?
> 
> Hi
> 
> The GPS constellation repeats roughly once a day. It is not at all uncommon to have a “worst case” sattelite  geometry for a given antenna location. If you have one, it will repeat once a day and show up as a bump in the timing out of your GPS module. If you track long term data, it will / may / can keep you from getting to the sort of stability you would expect in the 100,000 second range. It’s one of the main reasons that things like GPSD-Rb’s lock up with time constants much longer than 100K seconds. Yes having a Cs or something similar helps a lot looking for this sort of thing. 
> 
> Bob
> 
> 
> 
> > On Oct 19, 2014, at 9:26 PM, Bob Stewart <bob at evoria.net> wrote:
> > 
> > Hi Bob Camp,
> > 
> > 
> > In your response to Chris, you said: "Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. "
> > 
> > Could I ask you what you meant by these "once a day issues"?  Was this a general comment, or was it about something specific?  As you know I'm working on a GPSDO and am doing a lot of testing, so if there's something else I should be looking for, please let me know.
> > 
> > 
> > Bob - AE6RV
> > 
> > 
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