GPS Antennas, question of precision

Hi. Can the passive antenna I connect to the module (ublox m8q) affect the precision? Example: Two antennas from different manufacturers that receive the same number of satellitesdifferent precision is it possible?

And my second question:

What are your experiences with SBAS? The premise is to improve precision. But can it negatively affect the precision under certain circumstances?


Of course.

If the antenna is poor, the number of satellites recieved with good signals will be reduced.

Under weak signal conditions location precision\accuracy is normally degraded, sometimes significantly.

I mean, is there the same number of satellites on two different antennas or the precision can differ?

Not at all sure what question you are meaning to ask.

Please describe the project where you consider this significant ?

The project is a boat on the water. I reach the point marked out on the autopilot. I noticed that some of the antennas I use have a fix with fewer satellites, but are more precise, and I wonder what the point is ... Especially when the boat is close to the shoreline, there are big differences in precision.

When you are far from the shore, it's pretty certain that you have an excellent view of the sky. Close inshore, perhaps not so much. That can have an effect of the precision of your fix.

There are two effects here I think - the antenna radiation pattern and the basic sensitivity. If an antenna is less sensitive towards the horizon you'll only get the high up satellites, leading to lower lateral precision. If is isotropic but low sensitivity you might get fewer satellites but some of them on the horizon and thus better precision.

The error ellipsoid depends strongly on the angular distribution of satellites that you can read. If you only are sensitive towards the horizon the vertical error will be large. But of course the closer to the horizon the more atmospheric absorption anyway.

In practice a fairly isotropic antenna is going to do well, and like all antennas needs to be kept away from metal objects so its radiation pattern isn't disturbed.

Indeed so.

And therein is the problem with using a standard GPSs for accurate location.

Whilst one setup may well on average be better than another, both setups are subject to location errors.

So whilst a notionally good set up might be a lot of the time within 2m say, it could still be 5m or more out and you dont know when this happens.

GPS modules output the HDOP in the $GPGGA sentence, for what its worth.

Yes, I know that.

My understanding is that HDOP is just an estimate of position accuracy and cannot provide an absolute measure of position error.

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