Failed to receive complete datas ? with uBlox 7N

0 votes

Hi. I'm not able to use ucenter's graphical tools with my UBLOX-7N.

I receive datas from the module by checking the text editor but they seems to be uncomplete. I tried it outside in a field, and still nothing...

Where am I wrong ? Should I add an SMA antenna instead of the integrated antenna ? A firmware ?

I put a video showing my problem right here.


by TheStupidBeaver asked Aug 1, 2018
In addition to the appropriae comments made by clive1, other reasons that explain your symptoms are:
(Fault of the source of the board ---)
o    counterfeit product,
o    not built or tested properly,
o    improper or inadequate components used.
o    no RF filters on the interface lines (which allow radiation from fast transitions on digital lines)

(Your fault ---)  
o    Nearby RF interference e.g from your video camera (as a class these are notorious for jamming GPS receviers) , from your nearby laptop, desktop, video monitor, wireless/wired router, ethernet or USB cables, switch-mode power source, other test or hobby equipment.
o    Noisy power supply to the board.
o    ESD damage to RF section through mishandling of the onboard antenna (with no ESD protection in the design since an ESD protection device costs an exhorbitant  US$0.10).
o    Completely inadequate ground plane for the board (even a patch antenna needs a proper ground plane)
0 votes
Looks to be a fake NEO-7N

Realistically you are going to need to be outside, with a clear view of the sky for that antenna to pick up anything.
by clive1 answered Aug 1, 2018
It's kinda awkward to integrate such an antenna if you have to fly into the sky to use it... I had no signal from any satellites, I don't think the integrated antenna can be that bad. I want to ensure myself first the problem isn't coming from me before buying an SMA antenna.
You appear to be in a building, GPS signals are weak and don't penetrate buildings well, the penetration is usually left to the kinetic delivery portion.

Go outside, place the unit on a picnic table with the ceramic antenna laying horizontal, pointing upward.

>>I don't think the integrated antenna can be that bad.
Says a guy getting no RF signals at the receiver input. You don't have two units to compare/contrast, and you don't have a different or roof mounted antenna which is demonstrably functional.

Go outside and see if you can pull any signals, 32 dBHz would be borderline functional, I'd really want to see numbers in the 40-50 dBHz range for a significant portion of the visible satellites.
0 votes

It is possible that it is a counterfeit. I did my little investigation and I found clues for this possibility. I'll still test what @grampy said right after for more clues and I will give my results then. I tried what you said @clive1, and I had really poor signal for a really short time (minimum : 10 dBHz max : 28 dbHZ) according to the "statistic view" of u-center.

Therefore, I'm always in "No FIX".

Here are my clues for the counterfeit possibility. On this image you can see there is no FIS or EXT entry (on the right side is my text console; on the left is ublox' forum page. According to this, my Flash parts are missing (conterfeit theory).

I also have the counterfeit's drawbacks described by Ublox's services.

Do you think that, even it's a counterfeit, I can have better results with an SMA antenna instead of the integrated one ? My project is'nt that big, it's just for practice.

by TheStupidBeaver answered Aug 2, 2018
Not used that specific board, although have seen it at a couple of online vendors.

My concern here is how it switches from on-board to external interfaces, there looks to be an LNA, and I'm not sure they switch it on/off, would need to review a schematic.

These type of boards often ship with a $5-6 GPS Antenna, these tend to have 30-40 dB gain, and are quite serviceable. Often with a magnet inside they can be stuck on a small metal plate or car roof and be very effective. So not a huge investment to try, although inconvenient if you don't have one to hand.

A lot of the fake NEO-7M modules use a TCXO, and work just fine. The vendors would do better putting their own brand label on these modules, and stand on their own merits, rather than pretend to be something else, but apparently this isn't the Chinese way of doing things.
For a quick assessment, issue the UBX-MON-HW command and note the values for AGC, noise, CW jamming.
If the UBX command does not get a response, then the core chip is not u-blox.
If AGC value is high, then the RF section is faulty somewhere (ESD damage, no voltage to active antenna, bad solder joint, etc --- needs hardware troubleshootin)
If AGC value is low, this indicates high gain (generally not a problem unless below 10% which compromises jamming mitigation),  or very high external noise, an oscillating LNA (excessive gain).
If noise value is broad indicator of RF function, CW jamming indicator should be below 5%.
Aside from this, its hard to troubleshoot remotely.
If my LNA is working, it means that my signal without LNA must be worse. I do not find a way to see if my LNA works, or how it works, with u-center. But it seems to have an LNA control and no LNA supply on that module according to the datasheet. I bought an SMA antenna on the web and I'm waiting for it anyway. If problems continue, I'll try with another module.
So here is what I get. I can receive messages from UBX. AGC value is high as you can see (the image is below), and CW jamming indicator is below 5%.
The GPS signal is in the noise floor, you're not going to see it on a scope/analyzer, the receiver correlates a pseudo-random sequence over several microseconds to pull out a signal.
0 votes

Here is my monitor.


by TheStupidBeaver answered Aug 2, 2018
AGC is consistent with passive antenna.
Unless antenna monitoring circuitry is part of the design receiver would not know antenna status.
0 votes
Hmm. Right now it seems I can't do anything. I'm still glad to see I can have a signal even if it's a poor signal. Which means I can dream of a better signal if I use an additional SMA antenna. I will give my results as soon as I receive this antenna. Thank you for the support @Grampy @Grampa @Clive1, you are in the top 3 (forum's rank), I really am lucky ;')
by TheStupidBeaver answered Aug 2, 2018
From a close look at the PCB, it appears that
(A) U2 may be a switch that transfers from on-board patch antenna to external, SMA-connected active antenna.  Since there is no obvious mechanism to control the RF switch, it must be triggered by (a) sensing a load current on the SMA connector, (b) requiring a command to activate one of the NEO GPIOs, (c) the PCB designer assumed (wrongly) that NEO-M8N LNA-EN is automatic and flips the U2 switch.
(B) U2 is an LNA that amplifies the signal from the patch antenna, and if an active antenna is connected to the SMA connector,  the board designer's assumption may be that the external active antenna will simply overwhelm the signal from the on-board patch.   If (B), the assumption is a flaw:  two antennas cannot be connected simultaneously.

To resolve this, you can try to find the manufacturer and post the schematic of the PCB.  Or you can just try a  more standard, trusted, simple product that does not have an on-board antenna and expects usage of an external active antenna.

While I appreciate your thanks, with all the time we have all spent on the u-blox forum trying to support what is likely a NEO not made by u-blox, without seeing any success for all your efforts, strongly suggests that maybe you should just re-start with a trustworthy product purchased from a trustworthy source.
My final contribution.....  here is the board

Buyers comment on the "zero signals when using onboard patch" and "need to solder in a capacitor"
The RF implementation on this is board is flawed from several aspects.  Very poor performance is expected and I expect even with an external antenna, performance will be below expectations compared with properly designed boards.

Good luck with re-starting your project with a reputable board from a reputable supplier.
0 votes

Months have passed and I finally succeed to have a fix :D

My first module seems to be counterfeit, as I cannot upgrade with the firmware. The seller re-send me another module. I suceeded upgrading with ublox firmware and having a fix. With the integrated antenna, it seems almost impossible to have a fix. But with my external antenna, there's no more problems. My signals are between 20-30 dbHz.

by TheStupidBeaver answered Oct 6, 2018
Good that you achieved some reception. Note that other product implementations of u-blox 6, 7, 8, M8 would be displaying signal levels above 40 dB-Hz (with some in the high 40s) for most satellites.
For the range 20-30 dB-Hz, the expectations are: best cases: long time-to-first fix and poor position accuracy, most cases: no position fix.
There are better products on the market.
Yeah I noticed it took 20-30 seconds before having a fix. And sometimes, if I do not have a clear view of the sky I have "no fix" (especially in buildings). But when I have a fix, I can keep it for a really long time. I'm gonna make some experiments tomorrow to try to improve the signal.
Getting a fix in 20 to 30 seconds is OK - so there must be some signals better thatn 30 dB-Hz.  Your goal should be 8 satellites with signals above 36 dB-Hz with some C/N0s above 45 dB-Hz.  Again, current GNSS signals are not intended for indoor use so don't waste too much of your time trying to get an accurate position indoors.
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