[time-nuts] tracking position & orientation

[Eric Scace]

   Thank you, everyone, for your enthusiastic guidance and observations to my quirky question.

   Quite a few mentioned the difficulties in measuring rotation over a short baseline. In response to the question of “is there another measurement point 10 miles away”, the quick answer is yes: NIST is on the opposite side of Boulder City from me.

   The question of a sturdy — i.e., dimensionally stable — antenna mount brought to mind something I learned during my home inspection. My house is built at the foothills of the Front Range in North Boulder. Soils there include a kind of clay that swells significantly when exposed to water. As a result, house foundations are build on a system of screw pilings that go down to bedroom. The house’s cellar floor is a concrete slab poured on corrugated steel plates supported by cross-web girders that sit on these pilings. The cellar walls (to which the higher-precision pendulum clocks are mounted) are poured concrete that also rests on these pilings. It seems the house foundation is probably a better reference point for antennas than something sitting on the ground at the corner of my (tiny) lot.

   Of course, my house and the neighbors’ houses are obstructions to signals for an antenna attached directly to the foundation walls.

   The plan was to install two antennas (for two GPSDOs) mounted on short roof-penetrating metal tubes secured to the roof framing, just high enough to clear the neighborhood’s rooflines. This will give full sky access (except for the portion obscured by the foothills of the Front Range, a problem that plagues NIST as well). For time purposes, my understanding is that this should be fine.

   For millimeter-scale position determination, this sounds like a more difficult situation. The house is generally wood framing with some structural steel elements (not in useful locations). Position measurements would contain noise from the diurnal/seasonal changes of the house framing. Maybe that could be averaged out?

— Eric

> On 2019 Nov 22, at 00:36 , Hal Murray <hmurray at megapathdsl.net> wrote:
> 
> Measuring rotation will be tough if your 2 stations are only 100 ft apart.  Do 
> you have a friend 1, 10, or 100 miles away?
> 
> PS: Make sure that your antenna mounts are sturdy.  You don't want them 
> drifting as the house ages or you bump into them.