Issues with new GPS modules

[PhysicsGuy]

I'm having trouble with some new GPS modules I recently purchased. I have three new boards with u-blox GPS modules (a mix of NEO 7M and NEO M8L) and none of them will get a fix even when left under an open sky for several hours.

Background: About 3 years ago, I built a GPS transmitter using a NEO-6M module and an Adafruit LoRa radio. It works great. This year, a friend got me thinking about an upgrade to add Bluetooth to my system and then send the received GPS coordinates right to my phone. I decided it would be good to upgrade the GPS modules at the same time. So I purchased the NEO M8L from an Amazon seller and two NEO-7Ms from an eBay seller in China. However, upon powering them up, none of the units will ever get a fix. To my surprise, all of the units seem to be built on the same board. Here's a picture (the NEO 7M is on the left). Other than the GPS module, the only difference is that one board has an SMA connector already soldered on.



Not shown is a patch antenna which is mounted to the other side of the board. My experience with the system I built a few years ago shows me that the patch antenna is more than sufficient for this application. So, I don't plan to use an external antenna.

All of the boards included a USB interface that I found to be enabled. For more testing, I connected them via USB to the u-center software on my Windows pc. I was able to see that the board is sending NMEA sentences but, since the unit never gets a fix, there is no location data. They seem to be recognized as genuine u-blox modules (or very good clones) and the u-center software allows me to review and edit the configuration.

Does anybody have experience with these boards? Did you have to do anything special to get a fix? Any feedback would be appreciated.

Thanks.
--MARK NAR 65148 L1

 

[SparkyVT]

Have you connected them to U-center? I suspect they may be fake. This happened to me a few years ago and now I only buy from Mouser or Digikey. What is the initial message on power up? It should give you some text about what type of chip it is.

 

[OzHybrid]

Have you connected them to U-center? I suspect they may be fake. This happened to me a few years ago and now I only buy from Mouser or Digikey. What is the initial message on power up? It should give you some text about what type of chip it is.

Unfortunately there are a lot of these. Looks like a duck, but doesn't quack like a duck.

 

[SparkyVT]

Sorry, I missed that you said they are recognized by U-center. If so then they are probably good.

I also had an issue with the antennas on these units. Does it use a ufl connector? Those are flimsy and can lose connectivity easily.

 

[PhysicsGuy]

Sorry, I missed that you said they are recognized by U-center. If so then they are probably good.

I also had an issue with the antennas on these units. Does it use a ufl connector? Those are flimsy and can lose connectivity easily.

Hey Sparky, It's good to hear from you again, and thanks for your reply. We exchanged a few messages when I was designing/building my first GPS tracker. The info you provided back then was very helpful. Thanks.

Yes, I'm able to connect all these units to u-center and view/update configurations. If they are clones, they are very good ones . Here's a screenshot from the u-center text console at startup of one of my NEO 7M units.



The ceramic patch antenna is mounted to the back of the board and soldered directly. It does not use a ufl connector. All the boards came with an SMA connector (and presoldered on the NEO 8). To save on space/weight, I don't want to use an external antenna. The patch antenna worked just fine on my original tracker. I've watched the u-center displays with these boards and it's rare to see them pick up more than one satellite! And, the signal level is low compared to what I see on my older NEO-6M board. Strange..... maybe I should suspect the antenna. Some more testing may be in order.

I like using the u-blox modules mainly because of the u-center software. The software has a file transfer capability and I can use it to create multiple configuration files, store them on my PC, and then upload it to the module before I go fly.

Thanks again.
--MARK

 

[OzHybrid]

With the SMA connectors you need to watch out for the center pin length on the males. The female connector can have a coupling capacitor at the base. If male is allowed to go too far because the SMA female is not mounted through a case with a locknut, you can screw the male too far in damaging the coupling capacitor. This happened to me with a Telemetrum ground station.

 

[OverTheTop]

Given there is a SMA connector for an antenna, is the patch even connected? I would be trying to confirm as getting two antennas to play well together is not just a matter of connecting both. Baluns and matching networks are necessary. Not sure an inexpensive GPS receiver would bother.

 

[PhysicsGuy]

With the SMA connectors you need to watch out for the center pin length on the males.

Thanks Norman, good to know. The connectors that came with these units have at least 3/8 inch of threads on them so I don't think any of my antennas will go on that far.

--MARK

 

[PhysicsGuy]

Given there is a SMA connector for an antenna, is the patch even connected?

Good question! I definitely see solder connections where the antenna and board meet. But I'm beginning to suspect that it is not connected or is a very poor antenna. Unfortunately, I don't have the test equipment and steady hands to look at the RF input pin on the module (dang those pins are close together). I'm doing some tests now with an external antenna and the difference in performance is amazing. I will try to post an update later this weekend. I've had success using the patch antenna in the past, but as they say -- past performance is no guarantee of future results.

--MARK

 

[UhClem]

The RF inputs appear to be extremely sensitive to static electricity. Or at least whoever wrote the warnings in the data sheet thinks that it is. This seems to be pretty common across all GPS receiver chipsets.

Some chipsets have separate pins for internal and external antennas. I looked at the data sheet for the NEO-7 and that isn't the case for it.

This external antenna you tried. Is it an active antenna with gain? If so, then check the gain settings on the GPS chip. Setting it higher might be just what the passive antenna on the board requires.

 

[PhysicsGuy]

This external antenna you tried. Is it an active antenna with gain? If so, then check the gain settings on the GPS chip. Setting it higher might be just what the passive antenna on the board requires.

Hey David, Thanks for your input! Definitely appreciated.

I've had interesting results with the external antenna and don't completely understand why. Unfortunately, I don't have any kind of external GPS antenna (active or passive). The only thing I could come up with that had an SMA connector was the rubber duck antenna on my handheld radio (Yaesu FT60 2m/70cm). So, I gave it a try on my NEO M8 module and was pleasantly surprised (astonished might be a better word). The module went from seeing 1 or 2 satellites and never getting a fix to suddenly seeing 10 or 11 and having a fix in only a few seconds. Now this antenna has fairly wide receive coverage, but I doubt that it includes the GPS frequencies. But it was still way better than the patch antenna. Watching the data in u-center, I noticed improvements of 8-10 dB.... that's amazing.

Unfortunately, the external antenna did not have the same effect on my NEO-7M modules. I saw no improvement on either of them.

Although I'm somewhat familiar with u-center, I'm not familiar with how to adjust the gain settings. I will go research this weekend. But there are SO MANY config settings, if you could point me in the right direction that would be great.

Thanks.
--MARK