I am quite sure i have seen a topic somewhere but cannot find it so try it agian.
What is the best way to set up the GPS antenna for a ROVER.
Do I position it all the way on top?
I have heard/seen some people using a sort of backplate to he antenna .
How big should that be?
Aluminium ?
Rouns or square or does it not make any difference?
Also I want to use the piCam , will it interfere with the GPS?
My setup is working but in the outside around (not inside) buildings/barn the position jitters to much to use for navigation.
I need a more presice reading.
Does the antenna have a direction relative to the rovers front?
The antenna I have is the one that was shipped with the first batch from indigogo.
It is a challenge to achieve good gps performance in rovers, here are some advices:
Install the antenna as high as possible, you have probably seen some rovers with antenna poles as high as 1-2 meters.
Use a ground plane about 100mm in size, shape should only matter for small ground planes, but it is better to stick to the shape of the antenna. Brass or copper works best. The easiest and most lightweight would be a piece of PCB.
You can position antenna in any direction.
On the Indiegogo batch we had a very gentle u.fl connector. Make sure that it is not damaged and is properly fixed.
The best approach for improving GPS performance is to connect to u-center, as shown here. On the right you will see bars that indicate carrier to noise ratio. In general, for any system you integrate GPS in (not only for Navio) you should observe SNR with all the equipment running. SNR is the best metric to evaluate your GPS installation.
Under clear sky, with a good ground plane several satellites should be close to 50 dB/Hz, if they are closer to 30 you will still get a fix, but performance will be degraded.
This approach should be repeated when you add new equipment. Try with, without and observe SNRs.
Thx Igor,
Excellent tips, the GPS works ok outside it gets a fix within a couple of minutes. Do I need to calibrate the GPS in some way? With APM Planner and googles maps as a background the map does nor really match the actual position of the rover? If I run it on the driveway, on planner it runs over my house!
Anyway I will make a ground plate for it see if that hads some performance.
Also is there an open source alternative to u-centre software, u-center does not run on linux i am afraid? I have seen an android app see if i can use that.
You can run u-center under vine on linux. Not perfect, but it works. Not sure about the alternatives, it is still the best GPS evaluation software out there. Android app would only let you work with built-in receiver afaik.
Keep in mind that google maps might not be perfectly aligned with real world in some places. There is no calibration required.
I happen to have 0.01 degree range location error on my Navio+.
On the moment, the satellite count was aloud 10.
Fixed position but wrong place on the map.
BTW, the reception of satellite has improved wider gap between top of the Navio+ and bottom of the GPS antenna shield. Original gap was 25mm. 50mm gap improves satellite counts by u-center software.
@igor.vereninov Can you explain what the actual function of the ground plane for the antenna is. Does it just act as a shielding for the noise from the other equipment or is it in increasing the size of the antenna reflector in some high frequency magical way?
Edit: Because if it is just acting as a shield wouldn’t it be more effective to shield of the noise at the source, eg. the pi-cam?
Most antennas require ground plane to operate properly, if you read the datasheet most of them state “measured on a 100mm ground plane”. Smaller ground plane or lack of it would result in a shift of the central frequency and lower gains. Large ground plane also protects from re-radiated signals, that cause multipath.
Noise should better be shielded at the source, @mfm is absolutely right.
I was curious and did a little reading. It is indeed that a antenna groundplane is acting as a reflector and ideally it should be Lambda/4 in size.
According to this something between 48 and 60mm should be ideal. GPS uses the frequencies 1575.42 MHz (190.4 mm) and 1227.60 MHz (244.4 mm).
This u-blox application note says the groundplane should have a surface area between 50-60 mm2
Edit: That u-blox pdf is really nice. Very informative.
