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?
Replies
Thanks!
Looking forward to testing it!
Hi all,
I just came across this: http://www.csgshop.com/product.php?id_product=202
Cheers,
Thorsten
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
Hi Thomas,
Can you use the 3DR configuration file for all the ublox M8x series?
I thought this was exclusive for the LEA-6H GPS module.
Regards,
Geert
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.
I hovered with poshold today while testing different props. Vibrations are very good, but the copter twitches ever so subtly. It doesn't do it in stab.
I'm wondering if EKF is causing this, meaning it is preventing an illogical move based on faulty gps data ala INAVErr, so it must constantly make minute adjustments which come out as "twitches". I was going to disable EKF to see what happens, but maybe it's not a good idea.
Not much activity on the subject lately.
I have had 3 wonderful 30 minute flights on my Hex using 2 M8N's..The INAVerr does go to 255 around the 2 min mark , but as ample posts here as well as on rcgroups have suggested this used to occur with the old Neo6m as well as the original 3DR GPSes, hence I am a bit less concerned while flying GPS modes...I do not see any twitching whatsoever in loiter..I have not tried Poshold but I will and get back if I see any twitching...I decided to ditch the GPS ground plane/shield idea coz' its not needed as I don't have anything interfering on the GPS band (I found this using a spectrum analyser) and also I don't think I am skilled enough to pull this off without making my GPS performance worse....
If anyone has already built a shield or a ground plane for this specific GPS+antenna config i.e CSGshop M8N then I guess all of use would be interested to see the difference is performance
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.
Out of curiosity, are you using a 25mm x 25mm M8N or the 50mm x 50mm unit?
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