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?

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  • Hi!

    I need your recommendation...

    I am currently building huge X8 octo. I want to buy possibly the best GPS I can get for Pixhawk...

    I don't want to go with Zubax GNSS 2 because I don't want to screw up any settings...

    On RcGroups they recommend me CSGShop. I will probably buy their GPS. The question is which one. I suppose that I should hgo with PRO version Actually I don't understand what are 'double SAW and LNA systems' that PRO versions have over XXL versions...
    Should I choose M8N or M8T?

    I heard that AC 3.4 will have GPS redundancy again. How will it work?

    Thank you!

    • Hi Adam, could you please describe what exactly about configuring APM for use with Zubax GNSS 2 makes you uncomfortable? We'll try to improve our documentation based on your feedback.

      Thanks!
      Pavel.
      • Well I understood that your GPS is not plug and play...

        And I am afraid that I could screw up something.

        But I can change my opinion! :)

        I am studying it know and it doesn't seem so complicated after all...

        • Support for UAVCAN sensors in APM is a bit lacking, so the steps described in the tutorial are needed to work-around this manually. Hopefully APM will improve in this regard in the future. For purposes of comparison, Zubax GNSS 2 can be used with PX4 as a plug-n-play device - no configuration needed.

          I don't think it's possible to screw something up following the tutorial since it's really straightforward; even if you get in a bind you can always ask for assistance at the support forums.

          Pavel.

          • Hi Pavel!

            Thank you for your reply...

            What are the advantages over GPS from CSGShop? (except barometric sensor...)

            Thank you!

            • Zubax GNSS 2 features an embedded SAW/LNA, a large high-gain patch antenna, u-blox receiver with TXCO oscillator (u-blox M8Q, the latest generation), and shielding which makes the device more resilient to EM interference (we successfully used Zubax GNSS 2 on a UAV with an embedded x86-64 computer where other GNSS receivers would perform poorly because of EMI).

              I'm not selling hard I'm just stating known facts ;). You can always google or search this website to see some public feedback.

              • Great! :)

                Unfortunately I can't find any dealer...

                Onedrone.com has only Zubax GNSS v1 and NicaDrone.com has not Zubax GNSS...

                • Hi Adam,

                  I have been reading through your recent comments on this thread. I have a need for a receiver that has shielding and a magnetometer, and is easily configurable with PixHawk. It looks like Zubax GNSS 2 is a good option and is now available for pre-order at onedrone.com.

  • Doug

    Do you know if the battery goes bad if the time it takes to get a good gps lock increases? My M8 used to grab 6-8 sats in just a minute or so. Seems to take more like 4-5 now I don't get it. About the only thing I can think of is the battery. Thx

    • Another question for you.  How long has your GPS been powered off or shelved?  I know this sounds peculiar, but I have observed that GPS units that have been off for a period of time (such as a week) could take longer to reacquire the satellites due to the orbit of satellites are not fixed they rotate around the earth.

      Can you put a voltmeter on the battery to determine if the battery is dead or low?  By the way the batteries I have on my GPS units use a MS614SE type battery and are rechargeable.

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