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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Out of curiosity, are you using a 25mm x 25mm M8N or the 50mm x 50mm unit?

I don't know the root cause of the twitching, but it doesn't seem to do it in stab mode. It could very well be a tuning issue, but as all the PID's maxed out during AT, I'll probably wait until 3.3 (supposed to be really good for tuning) before using that again.

One thing that may be causing such high PID is the Sky Hero Spy has rubber isolators connecting the battery tray to the frame. Maybe when the copter is doing pitch/roll during AT the battery is jerking around a bit? I don't know, it just seems like a possibility.

What I do know is the copter was handling like a Greyhound bus with stock PID's.....nearly impossible to hold steady long enough to start AT.

Sorry for the slow reply. I use the beaglebone as a co-processor for my own stm32f4 based autopilot. There are some more details in the videos here and here if you're interested.

I am using 25mmx25mm antennas that come with the CSGshop GPS modules...

also I just got my modules replaced by CSGshop, I am looking forward to testing them to see if the BAD GPS HEALTH messages reduce

Hi all,

I just came across this: http://www.csgshop.com/product.php?id_product=202

Cheers,

Thorsten

Awesome!  I ordered one for testing.  Like to see how it compares to my other 25mm x 25mm and 40mm x 40mm NEO-M8N GPS units.  I will post my findings of each when this one arrives and I have it configured on one of my airframes.

That's actually a bit humorous considering I emailed CSGShop about interference issues and they said it was not a problem with their units, but a problem with Pixhawk.

@DG,

I am currently running a uBlox LEA-6H as the primary GPS and a CSGShop M8Q as the secondary GPS on my test bench Pixhawk and have not experienced any interference issues that I can detect.

I can say that the M8Q is not any better than the LEA-6H when it comes to satellite reception when programmed with the latest 3DR configuration file (hand programmed one parameter at a time).

Regards,

TCIII AVD

@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.

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.

Great! 

Is the compass working as well?

Yes, everything works, although support for barometer requires some hackery with initialization scripts on microSD card.

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