I have been gathering the parts for a UAV for a research project for a while, and I received my unassembled APM 2.0 with built-in MediaTek GPS kit in July, right before the APM 2.5 came out (it came with the parts for the voltage protection). Coincidentally, I never got the case I was told I would get. When I looked at it at first, I noticed a strange thing: the GPS patch antenna had some odd scratches on the edges of the metal. I looked at the documentation, and all the other images of the GPS module showed it as only usually having one score. Here's a couple pictures to explain what I mean:
Look at the GPS module, specifically at the line(s) on the edges of the actual patch antenna on the yellow ceramic plate. The documentation only has 2 straight marks on the GPS antenna, on the right side and top side, while mine came with scratches on all four sides that are neither centered nor of an even width. I'm not sure, but I think these may (not sure) be made during the manufacturing process when the antenna is being tuned to GPS frequencies. I attached the picture below, in case it doesn't load.
What my APM 2.0 looks like plugged in:
What the documentation says it should look like:
The GPS module had those marks on it when I took it out of the packaging. I at first they were insignificant, so I soldered the GPS shield on along with the rest of the connectors and voltage/reverse polarity protection kit. However, when I booted up APM Planner and connected the APM2, I got no GPS lock. The Planner: "No Lock." The APM 3DFix LED: blinks on and off intermittently every 1.5 or so seconds. I assumed this was because I was inside a building, and therefore normal, so I put it away for a couple months while I worked on other projects. Now, when I took it out today to test, I also got no GPS lock. I went through the usual testing, and got no GPS satellites consistently for the 20 minutes that the test ran. I ran this testing multiple times inside and outside where I am able to get a GPS lock on several devices, but still got no lock on the APM. It has never been mounted in a plane, connected to servos, or exposed to any type of electrostatic discharge or physical damage, and has never been powered through anything other than the standard USB cable to a computer port. That eliminates all of those options for it failing. I'm not sure if this is a QC issue with 3DR or MediaTek, or something else altogether. Is there any simple way I can fix this issue? If not, will 3DR offer me a replacement external GPS or some other replacement module? I should hope I won't have to order a whole new APM, since removing the shield is pretty much impossible, and there have been some issues reported with the 2.5 that I would prefer to avoid...
P.S. I attached two pictures I took of the APM in July, before I soldered anything together, and right after I finished.
-Paul
Replies
The patch antenna is on top of the ceramic substrate and, in your case, has the notches. As TJC3 mentions, various batches have various parts removed and it could very well be part of the 'tuning' process though I seriously doubt that each unit is tuned at the factory but.. who knows?
Looking over the documentation for the part, there was an external antenna option for the original chip:
Polarization Right‐hand circular polarized
Frequency Received 1.57542GHz +/‐ 1.023MHz
I would expect the onboard antenna to support something similar. If you felt lucky, you could bridge some of the notches. Heck, it ain't working anyway but before you do...
the basic MediaTek chip is on sale at the 3DR store right now. But then yours seems to not be performing well and is brand new. Sounds like a warranty issue to me.
-=Doug