[time-nuts] GPS Antenna on Tower.

Attila Kinali attila at kinali.ch
Mon Jun 19 12:00:44 EDT 2017

On Mon, 19 Jun 2017 08:52:37 -0400
Dan Kemppainen <dan at irtelemetrics.com> wrote:

> So, what sorts of things are done for high precision survey work? I 
> would guess a sturdy mount, good sky view, no reflections, good antenna, 
> no nearby radiators, etc. Those all seem like common sense stuff.

I don't know about survey work, but you can have a look at the EUREF[1]
stations. Most (all?) stations in the list[2] have pictures.

[1] https://en.wikipedia.org/wiki/EUREF_Permanent_Network
[2] http://www.epncb.oma.be/_networkdata/stationlist.php

> But for applications that really matter, what sorts of things might be 
> missing above. Obviously, really expensive silly things won't be done on 
> my site for a few GPSDO's, but it would be good to know what the issues 
> are.

You try to mount the antenna as sturdy as possible. The best is if
you have an open and level field and can put a nice block of concrete on
unmoving bedrock. If not, ontop of a well build building will do,
though the vibrations might not be negligible. People use also relatively
low towers (high towers tend to vibrate), of only 2-5m height. Again mounted
on a block of concrete, if the tower isn't itself a construction made
of concrete. The dome should be such, that you don't get a bird problem
and that snow does not stick. At the same time the dome should be
shaped in a way that does not cause any refraction. If your reference
station (which is in a nearby building in a temperature controlled room)
has any ultra stable reference oscillator (think of a Cs beam standard
or a hydrogen maser), then you also want to have the temperature and
humidity of the cable going to the antenna controlled. Ie. you put
the antenna cable into a tube and blow constant temperature/humidity
air through it.

Of course you can go even more crazy, but the temperature/humidity controlled
cable is about the most extreme I have heard of.

				Attila Kinali
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson

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