[time-nuts] Sub mm measurements with gps timing antennas?

[Bob Camp]

Hi

Both the receiver and the antenna have filters in them. The "affordable"
ones (no need to say cheap) are made from ceramics that have significant
temperature coefficients. If you are getting -40 to +30C jumps, they will
definitely have an impact on the filters phase / delay. That's going to make
sub mm work pretty tough.

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Attila Kinali
Sent: Wednesday, April 25, 2012 10:57 AM
To: time-nuts at febo.com
Subject: [time-nuts] Sub mm measurements with gps timing antennas?

Moin,

We've a customer who does sub mm measurements using GPS in alpine
enviroment. This is done using LEA-6T modules, logging of raw phase
data and offline post processing using long averaging windows.

Now, the customer had some problems reaching the precision requirements
and i'm wondering whether one of the causes might be the use of a
Trimble Bullet antenna [1] (3V type) and not a geodetic antenna. Can it be
that the phase center of the Trimble Bullet antenna isn't as well defined
as it should be for this application? Would the addional gain of the 5V
version help (35dB instead of 30dB)? Or should we evaluate a different
antenna all together.

A major restriction in this application is that there is a very harsh
enviroment, temperature wise. We have measured -40°C to +30°C jumps in
just 2h. Most of the time the devices are below freezing temperature,
but can go up to 50°C when in direct sunlight.

The next big restriction is, that this is a research project. So
there isn't as much money available as there should be to "do it right".

So, if someone could give a few tips how to improve things, this would
be much appreciated.

			Attila Kinali


[1] http://www.trimble.com/timing/bullet-gps-antenna.aspx?dtID=overview&

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