GPS Issues - Do I need a GPS Ground Plane & EMI Ring? - Discussions

So I read an interesting article about GPS antennas called "Adding a GPS Chipset To Your Next Design Is Easy".

A few points to bring up that I have concerns with dealing with my M8N antenna.

1. Active vs Passive Antennas. Two paragraphs within the article describes the difference between Active and Passive antennas. According to CSG Shop's specification for the NEO-M8N it comes with a low-noise regulator and RF filter built-in. So I'm assuming that it is a active antenna.

2. Antenna's requiring adequate plane. If I read that document correctly, these GPS modules may require a GPS plane as they are installed on a PCB that does NOT have 40mm of side to them.

Quote: "Generally, patch antennas in the 15- to 25-mm size range with a least a 40-mm (on a side) ground plane will give the best performance in portable equipment, but this may be too large for your application. This could force you to look at smaller antenna topologies such as linear chip antennas."

3. The next concern is to mitigate the noise interference from FC, ESCs, and PDB. Since my Y6B is set up with a clam shell cover and my M8N is attached under and close to the all the electronics, I may need to develop a shield "ring" connected to the shield can and then connect that ring to RF ground through an inductor at a single point.

Quote: It's common in VHF and UHF RF shielding to connect all points of the shield can to the PCB's ground plane. This can be a mistake at GPS frequencies, since the open-air wavelength of a GPS signal is so much shorter than UHF. Depending on the size of the shield can, if there is current flow across the can, the shield can will be able to resonate near GPS frequencies resulting in interference or de-tuning of the GPS RF.

By developing a shield "ring" connected the shield can and the inductor, the inductor will filter any EMI-induced current flow. The ring connected to the shield can will prevent any current flows or resonation issues.

I'm not an electrical engineer and need guidance from those out there who are. Did I interrupted this correctly? and if so I could use some help with developing the "ring".

Thoughts?

I am also posting this here per DG suggestion

Several threads here on DIYDrones and RCGroups have been opened to discuss about the explanation and what represent these INAVERR errors in performance monitoring in logs

This problem was reported end of January

Still no answers from 3DR/Dev guys, to tell us something about this INAVERR in logs

A ticket was opened in Github about that

I know that they are probably busy, but could be great if somebody could tell if this INAVERR error if indicating a problem or is not

I found a post from Randy who in last November was thinking INAVERR at 255 was not a "very good thing"

http://diydrones.com/xn/detail/705844:Comment:1482305

Reply by Randy on November 25, 2013 at 6:52am: Marcus,

Thanks for the info. Your copter missed one GPS message and went 0.07seconds without a fresh GPS update (you can see the 400ms jump in the GPS time between lines 2593 and 2606). You were in Loiter mode but it was so short lived it didn't upset the navigation at all. If it was -rc6 you would have seen a very slight twitch. If that INAVErr was 255 meaning it had maxed out the recording of errors I'd be more concerned. For now, this is consistent with what I'm also seeing which is that we're getting occasional missed messages which we still need to get to the bottom of but in low numbers it's not dangerous.

Replies

tshado March 15, 2015 at 5:27pm

I am also posting this here per DG suggestion

Several threads here on DIYDrones and RCGroups have been opened to discuss about the explanation and what represent these INAVERR errors in performance monitoring in logs

This problem was reported end of January

Still no answers from 3DR/Dev guys, to tell us something about this INAVERR in logs

A ticket was opened in Github about that

I know that they are probably busy, but could be great if somebody could tell if this INAVERR error if indicating a problem or is not

I found a post from Randy who in last November was thinking INAVERR at 255 was not a "very good thing"

http://diydrones.com/xn/detail/705844:Comment:1482305

Reply by Randy on November 25, 2013 at 6:52am

Marcus,

Thanks for the info. Your copter missed one GPS message and went 0.07seconds without a fresh GPS update (you can see the 400ms jump in the GPS time between lines 2593 and 2606). You were in Loiter mode but it was so short lived it didn't upset the navigation at all. If it was -rc6 you would have seen a very slight twitch. If that INAVErr was 255 meaning it had maxed out the recording of errors I'd be more concerned. For now, this is consistent with what I'm also seeing which is that we're getting occasional missed messages which we still need to get to the bottom of but in low numbers it's not dangerous.
- Developer
  
  Randy > tshado March 15, 2015 at 6:02pm
  
  @tshado,
  
  The Inav errors mean that inertial nav has not received a GPS update within 0.3 seconds. So that probably means that the GPS is running too slowly (i.e 3hz or less) or messages are being missed. I've never used one of these GPSs so I'm really not sure what exact technical issue is that's causing the missed messages.
  
  It's hard to say how badly this will effect inertial nav's position and velocity estimates but it will have a negative effect I think.
naitsuga March 13, 2015 at 5:01pm

Thanks Mark

the good thing to know with both logs, EKF is enable

we found 0 INAVEER. one of them.

I have downloaded. and will play with them tonight.

Still want to know if people flying without EKF enable will have same error indication.?

@Doug sorry, its kind of hijack your thread to attract more people involve and bring developer attention.

it's no 4 top discussion now hopefully the error indication is related to your thread.

Do we need to post about INAVEER on

http://diydrones.com/forum/topics/inaverr-is-it-the-gps-or-fc-or-ne...

its your call.
- Doug Walmsley > naitsuga March 15, 2015 at 5:52pm
  
  @ naitsuga
  
  I'm not upset, its good to see folks discussing all the issues with GPS signals and INAVERRs. I do however, wish to see more discussion on the EMI ring concept and GPS Plane designs for testing.
- DG > naitsuga March 13, 2015 at 7:12pm
  
  Personally I think this is the best place now because it is more for performing tests, finding solutions etc. whereas my thread was one big question mark as I had no idea what INAVErr really was.
  
  I did fly tonight and had the same 255 straight line, and don't know what to think because it flew so well in poshold, RTL and Land.
  
  OTOH there's the feeling still that something just isn't quite right.
  
  It does have an IMU mismatch issue which I hope to resolve in the coming week.
  - AKcopter > DG March 14, 2015 at 2:09am
    
    Guys
    
    I need some help building the shield,
    
    where do I find the RF ground on the CSG M8N to solder the shield to ?
    - MR60
      
      Hugues > AKcopter March 15, 2015 at 10:59am
      
      AkCopter, I have the same question.
      
      Soldering the RF ground to the shield is required to provide a lower resistance path that EMI currents will follow. Not soldering is not shielding anything; As Craig says, then the EMI sources should be shielded not to pollute the GPS (instead of shielding the GPS itself).
      
      So back to the question : where to solder the ground plane to the GPS rf ground? Anyone has pictures to show that clearly ?
    - T3
      
      Thorsten > AKcopter March 15, 2015 at 12:55am
      
      AKcopter,
      
      not sure if it is really required. See my and Craigs following comment:
      
      http://diydrones.com/forum/topics/arducopter-3-2-1-beta-testing?com...
  - naitsuga > DG March 13, 2015 at 9:13pm
    
    DG
    
    Would it be possible you fly without EKF ? with same pattern poshold, RTL and Land.
    
    Taking off with stabilize mode as if the 3D fix safety check is applied, otherwise it won't arm.
    
    just trying to scale down the probable cause.
    
    and if further possible you fly both ( still without EKF ) 3DR GPS / CSGShop Neo-M8N
    
    Apparently you flew with 3DR GPS with same issue high Inaverr (3.2. or 3.2.1) So using Neo-M8N is not necessary as the main cause.
    
    Just wondering , why 3DR haven't taken any action for this issue?
    
    Thanks
    
    Naitsuga
    - DG > naitsuga March 14, 2015 at 4:59pm
      
      I am in the process of putting new motor mounts on and isolating the IMU mismatch, but will do as you request after the copter is ready to fly.
      
      Below is the first "official" fight of this Y6. I know it is the 3DR LEA-6H because of the Nsat and Hdop numbers, which were not good that day and I hadn't received the M8N yet on that date. This copter started with AC-3.2/installed and EKF enabled. 3.2.1 is now installed.
      
      Takeoff was at ~11 minutes on the time scale. INAVErr rapidly climbed at about 22 minutes. Total time in the air was about 19 minutes.

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