Poor GPS Fix
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Our team is getting together a GPS mast kit we can send out for testing on Starling 2 Max. I believe your name is already on the list to receive it.
Regarding your question, the item you circled in blue is a 6-pin connector board that allowed me to extend the short cable using another 6-pin cable. It is kind of bulky, so i just taped over it.
In your implementation, does that look like you have two antennas stacked on top of each other? Can you please elaborate?
Also, did you get a chance to try out the GPS signal viewer in the
voxl-portal? how high were your SNR during your test in open sky?Additionally, as i mentioned before, the proximity of RC transmitter (within < 2 meters) of the drone seems to decrease SNR, so please check that. It seems the RC transmitter is sending out signal outside of 900mhz band, which affects GPS.
Regarding the upgrade mast kit, i am also going to receive it and test it to confirm that it performs similarly to my initial mast.
I am going to perform some more testing in the next few days. I know there are a lot of factors that can affect the GPS signal, i will try to summarize them all in a shorter write-up.
Alex
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@Alex-Kushleyev Thanks for the info. Yes your team has shipped a GPS mast kit to me and it should arrive tomorrow. Thanks very much for making that happen. I'll try it and let you know the results in the next few days.
In my implementation I did not have two antennas, only one. I did try the GPS viewer in voxl-portal and it worked great, much more convenient than Ublox Ucenter. The GPS signals I received were about 20-30dB in open sky with up to 9 satellites. Much better than before but not enough to get a lock. I did not power up the RC transmitter because I'm connecting exclusively with 5G Google Fi when the drone is outside (inside I use the USB cable). I've also removed the WiFI USB device just to limit the possibilities.
Looking forward to testing the mast kit.
Bob
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@ROBERT-JUDD , 20-30dB is still very low, so something else is going on. Ideally, majority of satellites in open sky would be above or around 40dB. If it is at all possible, can you try disabling the 5G modem and instead just use USB connection with adb forwarding to look at
voxl-portal: https://docs.modalai.com/voxl-portal-via-adb/The reason why i asked about two antennas is because it looks like you have two antenna stacked on top of each other in your picture. Or is it just a plastic mount?
. Maybe i am just not familiar with this GPS receiver you are using.I should be getting my kit later today, so i will test it out. In my early tests i was using the original GPS module that came with Starling 2 Max and it was fine ( you can see it in the screen shots that you also shared in this thread).
Alex
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@Alex-Kushleyev said in Poor GPS Fix:
I believe your name is already on the list to receive it.
Anyway we can get on that list too? We received our starling 2 max nearly a month ago now and have only recently been able to test it. We're happy with everything but the GPS problem makes this product borderline unacceptable. We just had a meeting where we decided to hold off on ordering 5 more starlings because of this issue!
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@Rodrigo-Betances , yes, absolutely. I will provide your name to the team.
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@Alex-Kushleyev That's just the PETG plastic mount that I 3D printed in the picture. I'm using the GPS receiver that came with my Starling 2 Max from ModalAI (3DR taoglas).
Here's what I'm seeing in voxl-portal with my modification. ModalAI's GPS kit should arrive today, and I should be able to send you results for that in a few days.
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@Rodrigo-Betances @Alex-Kushleyev @somalley OK I received the mast GPS fix from ModalAI and I've installed and tested it. I do get more satellites and the signal is enough to get a GPS lock, so I'm clear to fly at this point. The signal still seems a bit low but maybe that's just my location. I do have a clear view of the sky but there are tall trees not far away that may block satellites below roughly 45 degrees from the horizon.
IMPORTANT: The mast kit shipped with a ca. 10cm 6-pin cable with female JST GH connectors on each end. There is no way to connect that cable to the existing connector, and the cable itself is too short to reach the VOXL2 connector. I would suggest that one end be shipped with a male connector. Otherwise customers will need to make their own cable as I did.
Thanks for your help. Looking forward to reports from others.
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Yes, we are aware about the cable mismatch (sorry, the shipment was rushed a bit, but we will get it right!)
Regarding the satellite SNR, yest it still looks low. I would normally expect 10dB higher.
Are you able to test with disabled 5G modem? maybe pop out the 5G card or shut it down via a pin ( think we discussed how to do this long time ago).
I just received the same kit and will be testing it today and compare with my initial implementation of the mast. Will report back..
Alex
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@ROBERT-JUDD Nice! Hopefully we can get one of those kits too! Green with envy over here haha
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@Alex-Kushleyev This morning I tried to determine if the 5G service affects the GPS signal. I removed the SIM card, turned off the power using the commands below, and verified that I had no 5G service. I also tried various combinations of these, and I also tried disabling voxl-modem and rebooting.
voxl-gpio -m 1 out
voxl-gpio -w 1 0 # power off
voxl-gpio -w 1 1 # power onNone of these had any effect on the GPS signal. It remains essentially the same as the graph I sent yesterday (20-35 db on ca. 10 satellites). This does get a GPS position lock, however, so probably I can fly.
Looking forward to your results.
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We built upon the shield/cone concept since it showed promise and worked to eliminate any tiny gaps and cracks where EMI could potentially leak through. We designed and 3D printed a cone that would come together on both sides of the GPS antenna mount with enough spacing for them to slide around the posts. The inside of the cone and some of the post had copper tape applied to it. Aim of this is to shield the GPS antenna from all RF below the cone and only receive RF from above. As you can see from the screen captures, the results are very promising. I think my team and I can now move forward in testing that was previously blocked by the poor GPS performance. Hope this helps and inspires some other fixes.
You may want to consider a small RF shield cone on top of your mast.
Here are the results from our custom shield and testing.
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Very cool, thank you for sharing. We will try something like this.
Please note that we have observed that the wifi dongle, which is right under the gps receiver, causes some interference as well. Can you please try to repeat your test by unplugging the dongle completely?
A workaround to move the dongle to a different location is to use a different USB breakout board. Instead of M0141, use M0151 with a cable (JST GH to USB A Female).
Alex
