[time-nuts] GPS Antenna on Tower.
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
stations. Most (all?) stations in the list have pictures.
> 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
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.
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