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?

@Doug,

I ordered one for testing as well.

Regarding the reports about the zubax, which has a similar shielding but is unfortunately not yet running with AC3.3rc1, I am really looking forward to this one. As mentioned before I had no problems with the M8Ns so far - except the mysterious missing samples. But at least it will provide some additional noise reduction.

@DG,

I think it is not a problem of their modules or the pixhawk. It is simply the sensitivity of the M8N itself. It is a trade-off. If you like to receive more sats it will likely be more sensitive to interference. Hence you need additional measures. And I appreciate that they offer such a module. I am sure others will follow (if this kind of shielding helps on multirotors).

@Thomas,

this (satellite reception) is really strange! I made several tests and the M8N is always better (cf. http://diydrones.com/profiles/blogs/some-tests-on-gps-geotagging-an...). Apart from any number like sat count and PDOP the best indicator is RTL after longer flights. With an M8N the difference between take-off and landing position is usually < 1.5 m and in many cases < 1m. With the 6H is usually > 1.5m. But for sure this also depends on your location.

Regarding interference, have you tested bluetooth? I had big problems with that. I posted some screenshots above. But apart from that I agree that there is not that much interference. Anyway, it will be interesting to see how the shielded version compares.

Replies

- Richard Kennedy > Doug Walmsley May 22, 2015 at 5:50pm
  
  Wow... does that have a compass also? Just wondering what the EMI protection is exactly and if it has a compass perhaps it would help with that as well? Is that a micro usb for the connection?
  - Doug Walmsley > Richard Kennedy May 23, 2015 at 5:19am
    
    The GPS unit is the UBLOX NEO-M8T which does not include a compass on it. For me that's fine. I plan to install it on my OctoQuad as a primary GPS under clam shell and the Lea-6H and compass will remain external on a mast as secondary GPS and primary compass.
    
    The connection is a Mini-B type plug and not the Micro version.
T3

Thorsten May 10, 2015 at 2:31pm

Doug and all,

I just posted some test results regarding the influence of the ground plane:

http://diydrones.com/profiles/blogs/u-blox-m8n-ground-planes-antenn...

Thorsten
DG May 6, 2015 at 3:51pm

Does AC 3.3 support an external baro?
T3

Thorsten April 23, 2015 at 12:37pm

@Doug,

I ordered one for testing as well.

Regarding the reports about the zubax, which has a similar shielding but is unfortunately not yet running with AC3.3rc1, I am really looking forward to this one. As mentioned before I had no problems with the M8Ns so far - except the mysterious missing samples. But at least it will provide some additional noise reduction.

@DG,

I think it is not a problem of their modules or the pixhawk. It is simply the sensitivity of the M8N itself. It is a trade-off. If you like to receive more sats it will likely be more sensitive to interference. Hence you need additional measures. And I appreciate that they offer such a module. I am sure others will follow (if this kind of shielding helps on multirotors).

@Thomas,

this (satellite reception) is really strange! I made several tests and the M8N is always better (cf. http://diydrones.com/profiles/blogs/some-tests-on-gps-geotagging-an...). Apart from any number like sat count and PDOP the best indicator is RTL after longer flights. With an M8N the difference between take-off and landing position is usually < 1.5 m and in many cases < 1m. With the 6H is usually > 1.5m. But for sure this also depends on your location.

Regarding interference, have you tested bluetooth? I had big problems with that. I posted some screenshots above. But apart from that I agree that there is not that much interference. Anyway, it will be interesting to see how the shielded version compares.
- Pavel Kirienko > Thorsten April 23, 2015 at 12:42pm
  
  Hi Thorsten,
  
  Regarding the reports about the zubax, which has a similar shielding but is unfortunately not yet running with AC3.3rc1
  
  It is now. We got some assistance from APM devs, and I and Randy Batchell were able to confirm that 3.3rc1 actually works with UAVCAN-interfaced sensors. See https://github.com/diydrones/ardupilot/issues/2161.
  
  There will be some tutorials provided later this week that will cover this issue in more detail.
  - T3
    
    Thorsten > Pavel Kirienko April 23, 2015 at 1:07pm
    
    Great!
    
    Is the compass working as well?
    - Pavel Kirienko > Thorsten April 23, 2015 at 1:10pm
      
      Yes, everything works, although support for barometer requires some hackery with initialization scripts on microSD card.
      - T3
        
        Thorsten > Pavel Kirienko April 23, 2015 at 1:24pm
        
        Perfect!
        
        The external baro should help as well.
        
        I have no experience with the CAN bus so far. Is it correct that only one cable is required for all components, i.e. GPS + compass + baro, but more than one cable can be used for "redundancy"?
        
        Pavel Kirienko > Thorsten April 23, 2015 at 1:51pm
        
        Yes.

of 15

This reply was deleted.