Hi Attila, On 04/25/2012 04:56 PM, Attila Kinali wrote:
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&;
You can get both L1 choke rings and pin-wheels on Ebay for fairly reasonable money. That should help on multipath.
Another aspect is the temperature shielding of the receiver itself. If it can be kept at a fairly stable temperature would also help. Using a better reference oscillator could also be worthwhile. Consider what a FEI 5680 could do for you.
Also, the way the antenna is mounted can be relevant. Up, up and away... such that any funny reflections is below the antenna.
A simple temperature stabilisation might be to simply dig the GPS receiver down.
Cheers, Magnus _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
