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
Thorsten
What you did amaze me and very good job indeed.
I was the one deleted the question as I thought I posted the same question that John Deningss did asking for graphed to INAVEER, I want to figure out the timing on INAVEER elavated
So about the interference is kind emphasize the INAVEER
Without interference you still have INAVEER elevated.
and due to your work related the GNSS accuracy is really big deal.
Have you tried to run your work with EKF turn off but using M8N and see what is the accuracy related of your work. ( I assume the INAV only use DCM) and I would like to see the INAVEER on that setting if possible.
UBLOX M8 will capture more satellites and turn out to be nosier then too sensitive to interference.
but it will give more (pseudo-delta- ranges) and fuse to 3Dfix from each satellite and with high algo calc will include velocity make better prediction of accuracy ( I think this is EKF) I am not expert to explain it.
Do you realize that there is EKF feature can be turned on inside M8? I believe APM don't use it.
In the case high INAVEER ( without GNSS interference and without GNSS satellite degradation) on your graph and in the even EKF enable before you fly. This EKF will not kick in when the certain condition is not achieved like 3D fix and minimum satellites present while you are flying some people ok start flying without 3D fix at the beginning and find 3D fix achieved during flying. (Developer can correct me or explain better)
I would try myself if my pixhawk arrive .
Thanks
Naitsuga
Thanks, naitsuga!
Ok I deleted it from my mailbox so I was not sure who was asking :-)
No I haven't tried it without systematically. I remember that I made some tests but I switched back to EKF. EKF is much more secure and the better approach in general.
Yes I know that there is an EKF on the GPS as well. But I I guess what we need is to let the FC do the job.
As far as I know you cannot arm without a 3D fix. I will not try it :-)
Thorsten
Yes if your flight mode is Loiter prior takeoff you need GPS lock otherwise you cannot arm.
and GPS locked prior takeoff is not necessary for Stabilize ,Althold and Acro mode
since the GPS function might not need while taking off but
I have documented one developer a year ago stated stabilize and althold mode need GPS involve in APM code for AHRS very fascinating. (not GPS locked at taking off)
No, don't take risk on your expensive equipment to find this error :) ;)
as right now I can only guess the error come out if EKF enable without reasonable proof.
I fix my paragraph kind of confusing above( sorry I typed with my tablet.)
In the case high INAVEER ( without GNSS interference and without GNSS satellite degradation) on your graph and in the even EKF enable before you fly.
This EKF will not kick in when the certain condition is not achieved like 3D fix and minimum satellites present while you are flying
For some people ok start flying without 3D fix at the beginning and find 3D fix achieved during flying. (Developer can correct me or explain better)
With this one I am 100% sure that it shows BT interference. INAVERR started with 242 and was at 255 after 30 sec.
Now something really interesting: Bluetooth interference!
As can be seen, there is a relation to INAVERR. So this was a heavy interference and one should expect some influences. But in flights with no BT on board and thus much less interference I also see the INAVERR and as mentioned also on the 3DR 6H.
I have to check it but I am not sure if BT was installed on the flight I posted before.
There was a question (seems to be deleted) about the INAVERR of the flight where I analyzed the timing jitter. I am not sure which one it really was. But I looked at several flight I made that time and they all show INAVERRs. I picked out one (see below). This one was of a 48min loiter only flight. After 26min the INAVERR started to increase. Since the copter was in loiter there cannot be any effect of a sudden change in interference. What changed is the number of Sats dropping from 18 to 16 just before the INAVERR stared to increase.
Wow, amazing report and fantastic work on that link you provided. Thanks for that! Somehow I managed to have missed that at the time ..
So when everything is said and done, what is your take on the following as of today? Is the unshielded M8 as safe to use as the 3DR 6H? (Assuming, say >10cm GPS separation from FC).
With respect to observations of timing jitter, do you mean you actually witness physical twitches when flying, that is, you actually see them? (vs seeing signs in logs). Something you actually never see with 3DR GPS?
Irrespective it seems that further work and experiments with shielding will certainly make things much better.
Thanks, John!
OT: Yes strange thing, the post was listed in the Top 10 discussions only for a very short time and then dropped out of the top 20 - even though there was more discussion in this one post as in several others together. No idea.
Concerning your question I would say yes - but only if you are in a region where you generally have a good GPS signal reception. There are other posts at RCG reporting problems if there is not a good GPS constellation. But: even in my office I get a very good fix with almost no jumps after a while.
Maybe the best thing is to separate the GPS from the rest of the electronics as far as possible any also try to apply some shielding between the FC and the GPS.
Yes, I actually see the timing jitter. This is why I started looking into this issue. Maybe my system is a special "issue detector" :-) It is build for ling endurance and thus probably shows other characteristics compared to smaller copters with props spinning faster. It is hard for me to tell the difference between the 6H and the M8N, because when I started using the M8N I also started using the very high autotune values. If I lower the PIDs the twitches vanish (I'll make some tests to be 100% sure the next week).
PS: I am flying with EKF enabled since the very beginning. So I can only speak for this combination (EKF+M8N)
Hi John and Thorsten,
I am really happy to see people discussing this issue more. I would like to add that I have been flying with the the M8N and not running into any problems in flight even though my INAVerr values are at 255 and maybe it is not a flight critical issue as suggested and observed by most of us, but having said that we should be careful because this kind of approach to a problem may breed a false sense of security when going out and flying heavy camera ships like the ones I fly. I had seen these errors before when using the NEO 6M series of GPS's but what spooked me after using the 2 different M8N's (one from CSGshop and another one from RCtimer) was the high level of persistent "bad GPS health" messages I was getting on my HUD every now and then,sometimes I would also see the occasional bad GPS velocity messages even though the number of satellites were 18-21 and HDOP was 1.1-1.4 during the course of a 30 min hexa flight in loiter/auto and other GPS modes...I have attached a tlog in my post on the AC 3.2.1 beta testing thread which demonstrates this issue clearly here
http://diydrones.com/forum/topics/arducopter-3-2-1-beta-testing?id=...
any thoughts on this would be welcome
Doug :- I am planning on building a GPS shield like the one used by the autoquad guys but because our GPSes do not have a detachable antenna and also that the RF ground and digital grounds have to be separate I want to know where can I find the RF ground on the CSGshop M8N GPS to which I can solder the ground plane
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